
Subsections
Diseases of plants can cause great crop damages which may lead to hunger
disasters of great part of populations. Basic knowledge of the diseases of
plants and their cause are therefore important for everyone handling foods.
Despite all efforts to reduce crop damage due to plant diseases using
agrochemicals in the past 30 years the loss of approximately 10% remained
unchanged. As the crops have increased the total loss is increasing rapidly.
This makes a better understanding of phytopathology necessary[1284].
Phytopathology wants to bring a bectter understanding on the cause, the
circumstances and the progress of diseases of plants as well the interaction
of host-pathogenic agent.
Phytopathogenic agents are not pathogenic to mankind as moulds and bacteria
known as phytopathogenic cannot grow at 37
or are eliminated by
immunology of mankind. Phytopathogenic virus need plant louse or gnome zicada
as vectors as they cannot penetrate by itself. Human skin is not attractive
for these insects. The infection of these virus is therefore not possible.
However allergies to the spores of moulds such as Aspergillus and Penicillium
sp. and mycotoxins are of great importance.
The evolution of diseases in plants:
Diseases in plants develop in different phases:
Phases of a disease caused by mould:
Infection period: The infection period is the time between the first
attack of the plant by the pathogen agent and the moment in which he has
established itself in the tissue of the host.
Incubation period:The incubation period includes the infection period
and ends with first macroscopic symptoms.
Fructification period: Is the time between Infection and the first
reproduction of the agent in the host.
Some moulds have short periods and the whole life cycle takes only days such
as:
Polymyxa
Phytium
Olpidium
Some moulds need over half a year to complete their life cycle such as:
- Sphaerotheca mors-uvae
- Venturia inaequalis
- Puccinia graminis f. sp. tritici Its spores may be transportet in air at several thousand meters of altitude for a distance over 100 kilometers. That is the cause of sudden diseases never known in this region.
- Ophiostoma novo-ulmi: It is the agent of the death of elms and is carried by the elm beetle.
- Erwinia amylovora: Is being carried from pear farm to pear farm by birds or insects.
- Ustilago segetum var. hordei
Phases of a disease caused by other agents:
viral agents,bacteria, mycoplasma-like organism (MLO) and Rickettsia-like Organism (RLO) present a great reproduction with high number of organism before the fist symptoms appear.
Vectors of phytopathogenic agents
Bacteria such as Xylella fastidiosa, spiroplasma, mycoplasma-like Organism (MLO) and Ricketsia-like organism (RLO) need the help of other living cells or small animals like gnome zicade as vectors to invade another host
The cause of plant damage
- Climatic factors like excessive temperatures like heat or frost, heavy or prolonged rain, storm.
Care should be taken to avoid harmful environment such as may become in a green house under specific conditions.
Cucumber growing in a green house had a heavy attack of moulds destroying the flowers. The part of the plant coming through the door to the outside of the green house was free of moulds, the flowers could develop to ripe cucumber.
Instead of using fungicidal chemical to combat moulds one should seed remove the green house as soon as the first signs of mould attack
- Soil structure, heavily compact, water and oxygen circulation, chemical composition, content of manganese or aluminum
- Emissions like acid rain and industrial smog and dust
- Agrochemicals in excess which may evaporate coming down as rain like the herbicide atrazin
Susceptible to the disease: The host must be susceptible to the
disease. Some plants are resistant to different agents.
Organ specific activity: There must be an organ specific activity of
the agent. Some agents can infest only specific organs like flowers or roots
to which they are specialized. they cannot invade other parts of the plants.
Examples of organ specific activity are: Polymyxa betae for instance can only atta
Phase specific activity
Some agents have a specific activity to flowers. They have wait till the
blossoms open to attack the host, other have a phase specific activity to
leaves. they have to wait for the phase of leaves of a plant which is growing
from a seed.
Survival of the agent
Some agents have developed survival strategies to overcome the time between
one host to another. Virus cannot survive for long time outside a host cell.
They need therefore a vector cell to get through the time between where there
are no host cells available.The spores of the mould Polymxa can serve as
vector for the beet necrotic yellow vein furovirus for a period of many
years. Other agents have a saprophytic phase surviving in dead tissue of
the host of the culture period to another season to start a new outbreak of
disease. Saprophytic decomposition
Some saprophytes may decompose cell walls of dead material this activity also
can include living phytopatological agents. Mucor and Rhizopus moulds can
decompose cellulose of the cell of dead materials disclosing pathogen virus
which had invaded these cells. The virus is now unprotected and will soon be damaged.
Agrochemicals can interfere in the cycle of nature destroying normal
saprophytes which are enemies of harmful pathogenic agents.
Competition of nutrients
Saprophytic bacteria can multiply within an half hour. Pathogen mould need
days to multiply being so in disadvantage on regard of nutritional resources.
Production of antibiotics
Some moulds like Penicillium sp and Streptomyces sp =produce antibiotics
which act as natural enemies of some phytopathogen agents. Interfering in the
natural environment may destroy useful saprophytes boosting pathogens.
Virus with mycopathogenic activity.
Some virus act toxic on pathogenic moulds. The protection of the natural
environment is therefore important. Modern agricultural techniques should
protect the complex interaction of th different biological systems.
Hyperparasites
A parasite with phytopathologic activities may be invaded on its turn, by
other parasites ,like nematodes, bacteria and bacteriophages.
Parasitic plants can be half parasites having well developed leaves. They
depend only from water and minerals from the xylem of the host (Loranthaceae,
Viscaceae, Scrophulariaceae.
Full parasites have underdeveloped or no leaves at all. They invade the xilem
and the phloem of their host and get there nourishing substances
| Mistletoe |
|
|
| Loranthus europaeus |
South Europe |
Oak tree |
| Arceuthobium sp |
North America, Himalaya |
conifer |
| Viscum album ssp album |
Europe |
Apple, poplar |
| Viscum album ssp.abietes |
Europe |
Fir tree |
| Convolvulaceae |
|
|
| Cuscuta europea |
Europe |
Hop, shrubs, sugar beets |
| Cuscuta campestris |
worldwide |
Legume, sugar beet |
| Cuscuta reflexa |
Southeast Asia |
Citrus, Coffee, Litchi |
| Scrophulariaceae |
|
|
| Striga asiatica |
worldwide,except Europe |
Maize,sorghum, millet, sugar cane |
| Orobanchaceae |
|
|
| Orobanche cernua |
Mediterranean region |
Sunflower |
| |
East Europe,Africa |
|
| Orobanche crenata |
Mediterranean region |
Beans, lentil, chick pea |
| Orobanche ramosa |
Mediterranean region |
Tobaco, tomato, aubergine |
| |
Africa, Zentral and North America |
|
Virus: have only one type of nucleic acid, most of the time RNA, seldom DNA. Energy system ATP does not exist. Virus depend on ribosomes of host cells.
Mycoplasma-Like Organism (MLO)
Rickettsia-Like Organism (RLO)
Bacteria
Moulds
MLO, RLO, bacteria and moulds have usually both types of nucleic acids (RNA and DNA). Energy system ATP exists and they can multiply without aid of a host cell.
Phytopathogenic virus
Cauliflower mosaic (Caulimo): It is build of DNA.
Bacilus-shaped DNA (Badna)
Gemini virus
Phytoreo virus
Rhabdo virus
Tomato spotted wilt (Tospo)
Tenui virus
Cowpea mosaic virus (Como)
Faba virus
Nematode-transmitted polyeder (Nepo)
Potato virus Y (Poty)
Rye grass mosaic (Rymo)
Barley yellow mosaic (Bymo)
Southern bean mosaic (Sobemo)
Luteo virus
Tomato bushy stunt (Tombus)
Carnation mottle (Carmo)
Tobacco necrosis (Necro)
Diantho virus
Tobacco mosaic (Tobamo)
Tobaco rattle (Tobra)
Hordei virus
Fungus-transmitted, rod shaped virus (Furo)
Clostero virus
Turnip yellow mosaic (Tymo)
Alfafa mosaic (Alfamo)
Isometric labile ringspot (Ilar)
Brome mosaic (Bromo)
Cucumber mosaic (Cucumo)
Carnation latent (Carla)
Potato virus X (Potex)
The mould Pythium irregulare is a plant pathogen
[1127]
Pythium irregulare root rot and blackleg of geranium is a mefenoxam
insensitivity re-emerging disease. The fungus is also commonly isolated from
poinsettia, chrysanthemum, snapdragon, impatiens, and lavender. It is also
known as downy mildew. Blight, damping off, root and other rots.
Cacao swollen shoot badnavirus: It is a DNA- virus.
Tomato leaf roll geminivirus: DNA- virus.
Cassava mosaic geminivirus: DNA- virus
Rice dwarf phytoreovirus: RNA- virus
Tomato spotted wilt tospovirus
Rice grassy stunt tenuivirus
Barley yellow dwarf luteovirus
Potato leaf roll luteovirus
Beet yellows closterovirus
Citrus tristeza closterovirus
Potato virus Y potyvirus
Barley yellow mosaic bymovirus
Tobacco mosaic tobamovirus
Grapevine fanleaf nepovirus
Beet necrotic yellow vein furovirus
Cucumber mosaic cucumovirus
Prunus necrotic ringspot ilarvirus
Alfafa mosaic alfamovirus
Tobacco rattle tobravirus
| Pathogen germ |
Host |
Disease |
| |
|
|
| Gram-negative |
|
|
| Agrobacterium tumefaciens |
|
tumor |
| Agrobacterium vitis |
vine |
|
| Burkholderia solanacearum |
|
|
| Burkholderia caryophylli |
clove |
|
| Erwinia amylovora |
pear and apple |
|
| Erwinia carotovora |
potatos |
|
| Pseudomonas savastanoi |
bush bean |
|
| Pseudomonas syringae |
|
|
| Xanthomonas axonopodis |
|
|
| Xanthomonas campestris |
cabbage |
|
| Xantomonas hortorumpelargonium |
|
|
| Xanthomonas oryzae |
rice |
|
| Xanthomonas transluceus |
wheat |
|
| |
|
|
| Gram-positive |
|
|
| Clavibacter michiganensis |
tomato |
|
| Rhodococcus fascians |
pea |
|
| Streptomyces scabies |
potato |
|
Aspiognomonia veneta: It causes antracnosis on plane-tree.
Cryphonectria parasitica: causes disease of chestnut-tree.
Diaporthe perniciosa: Causes necrosis of the bark from apple-tree
Leucostoma cincta: Causes a disease of the bark of peach-trees.
Cochliobolus sativus: Disease of cereals.
Cochliobolus victoriae: Victoria disease of oats.
Didymella aplanata: Disease of raspberry.
Leptosphaeria maculans: Disease of the roots of rape.
Mycosphaerella arachidicola: Spots on leaves of the peanut-plant.
Mycosphaerella graminicola: Spots on leaves of wheat.
Mycosphaerella musicola: Disease of banana.
Phaesphaeria nodorum: Disease of wheat.
Pyrenophora chaetomioides: Disease of oats.
Pyrenophora graminea: Disease of barley.
Pyrenophora teres:Disease of barley.
Venturia inequalis: Scab of apple.
Blumeria graminis Disease of cereals: It cannot synthesize purines which are part of nucleic acid . Purines must therefor be taken from the host. It is therefore an obligatory parasite
Leveillula taurica: Disease of tomatos.
Podosphaera leucotricha: Disease of appel.
Sphaerotheca fuliginia: Disease of cucumber.
Uncinula necator: Disease of grape plant.
Aspergillus flavus:Disease of peanuts.
Penicillium expansum Rot of apple.
Claviceps purpurea: Ergotism of wheat. Claviceps purpurea forms ascospores can infect only blossoms. The best conditions of weather for the production of blossoms of the wheat most of the time occurs at a different time of the releae
Builts black sclerots which are formed from mycelium
Cibberella fujicuroi: Disease of rice.
Cibberella zeae:Disease of maize.
Nectria galligena: canker of apple-tree.
Diplocarpon rosae: Disease of roses.
Drepanopeziza ribis: Disease of redcurrant.
Mollisia acuformis: Disease of cereals.
Pezicula malicortis: disease of apple.
Pseudopezicola tracheiphila Disease of wine.
Pseudopeziza medicaginis: Disease of Spanish trefoil.
Magnaporthe grisea Rice blast.
Taphrina deformans: Disease of peach.
Taphrina pruni: Disease of prun.
Alternaria solani: Stains of the leaves of tomato-plant.
Septoria apiicola: Stains of the leaves of celeriae.
Alternaria sp.: Black rott of citrus fruit.
Aspergillus sp.: Black rott of peach and nectarine.
Aspergillus flavus produce aflatoxin B
. 100mcg in the feed of mice over a long period o time induces liver cancer in all rats. In Africa Aspergillus flavua can be very high. The disease of liver cancer is in Africa the highest of the world because of contaminated vegetable foods.
Botryodiplodia sp.: Rottenness of the banana-plant.
Botrytis sp.: Rottenness of fruits.
Cercospora musaeIs the cause of the Sigatoka disease of banana plantations.To fight the Sigatoka fungus a watery solution of chalk and copper sulphate was sprayed on the plants, later on mineral oil was sprayed by helicopters and crop airplanes.
Environment protection organizations have started a campaign to reduce toxic chemicals in banana plantations. The careless use of chemicals used against moulds and worms as well as weed killers being sprayed by crop planes over banana plantations produce sterility, skin diseases, asthma, damage kidneys and liver of the population living in this area.[1307]
Cladosporium sp.: Rottenness of fruits.
Colletotrichum sp.: Rottenness of citrus fruits, avocados and papayas.
Diaporthe sp.: rottenness of citrus fruits.
Diplodia sp.: Rottenness of the stem of citrus fruits, avocados, and papayas. Wet rottenness of peach.
Fusarium sp.: Brown rottenness of citrus fruits, pineapple and wet rottenness of figs.
Fusarium oxysporum var.cubense This fungus is known as agent of the Panama disease of banana plants. It invades the roots of the plant and destroys a banana farm. In 1925 and 1935 the Fusarium fungus was avoided by getting the plantations one to one and a half meter under water. After six month the water was drained and the plantation could be used again for five to six years. This method could be used only in valleys or plains.
Very sensible to Fusarium are the banana sorts Gros Michel. In Brazil, in some parts of Africa and Australia the Cavendish sort is being cultivated, also Lactan and Robusta are sorts which are resistant to the fungus Fusarium.
Geotrichum sp.: Acid rottenness of citrus fruits and peaches.
Gibberella fujikuroi is the agent of the Bakanae disease of rice. The fungus Gibberella produces gibberilin acid which is a growth promoter. The growth which is induced by gibbeilin thin and the plant can scarcely carry its own weight. Gibberella also produces a substance which is toxic to the roots of rice. The rice plants die on account of these substances.
Gloeosporium sp. Rottenness of pome fruits.
Leptosphaeria maculans Is worldwide the
most important pathogen fungus which attacks rape. There are pathogen and not
pathogen types.
Monilia sp.: Brown rottenness of fruits.
Monilia attacks cherry-trees, killing leaves and branches.
Nigrospora sp.: Rottenness of banana pulp.
Penicillium sp.: Blue and green rottenness of fruits.
Phomopsis sp.: Rottenness of the stem of citrus fruits and avocados.
Phytophthora sp.: Rottenness of citrus fruits, apple and strawberry.
Piricularia oryzae causes the Brusone disease blue dots which later change to brown color are the first symptoms. When the invasion takes place at an early stage of the growth of the plant no rice kernels are built. If it takes place later the stalk is bend under the weight of the grain in such a manner that the grain comes together with water or mud and gets lost.
To help against the Brusone disease solutions of mercury compounds and copper compounds were used despite their toxic effects.
Rhizopus sp.: Wet rottenness of fruits.
Sclerotinia.: White rottenness of strawberry.
Sclerotinia sclerotiorum Is a fungus which causes great damage on
rape. This fungus is in vitro highly sensible to alkenile-glucosinolates.
Sclerotinia sclerotiorum produces during the invasion of a plant high amount
of oxalic acid getting the pH down to 2,0 - 4,0. At the place of the invasion
nitriles instead of alkenyles are formed.
Trichoderma sp.:Brown-green rottenness of citrus fruits.
Venturia sp.: rottenness of fruits.
Black Pod and canker of cocoa trees
[1308]
The cocoa plant is particularly susceptible to disease from the fungus Black
Pod Phytophthora palmivora, affecting the pods and stems, cocoa beans become
spoiled. The disease spreads in 2008 in plantations of the Ivory Coast which
is the world main producer of cocoa. Other pathogenic moulds affecting cocoa
plants are Phytophthora megakarya and and a not yet firmly determined
species, Phytophtora capsici.
These fungus may cause diseases in other hosts like cashew nut, coconut,
rubber, papaya, betelnut palm, black pepper, pineapple, oil palm, breadfruit
and others.
Chemical control of black pod by spraying with copper based fungicide is widely
used, depending on the timing of rainfall, age of the trees, shade and other
local conditions.
Trunk injection of solution of phosphoric acid is described as a chemical
treatment to control stem canker. [1309]
The pathogen infects the leaves, shoots, flower cushion, roots and pods which
turn black.
When the disease spreads to the bark of the stem or branch it cause a canker.
The spores of the fungus is spread by rain, wind, flying beetles, all kind of
insects, bats and rodents.
Processing and chocolate manufacturing are in the hands of Barry Callebaut,
Cargill and Archer Daniels Midland, and Nestlé.
[1310]
Hovius and McDonald determine the efficacy of synthetic diallyl disulfide
(DADS) to fight white rot of onions grown on organic muck soil. The authors
concluded that DADS and to a lesser extent di-N-propyl disulfide (DPDS)
effectively reduced the incidence of Allium white rot on onions grown on muck
soils. Soil treatment with DADS.
According to the authors Sclerotium cepivorum Berk causes the disease white rot on several
Allium family, such as Allium cepa L., Onions, leeks, garlic, chives, shallots
and salad onions The disease is significant on organic soils.
Sclerotia germination and host infection are stimulated by alkenyl L-cysteine
sulfoxides released by garlic and onions. Garlic root exudates are precursors
of the volatile allyl and propyl sulfides that stimulate eruptive germination
of the sclerotia.
Germination can be stimulated by products such as natural onion and garlic
oil, or synthetic germination stimulants derived from petroleum, such as
diallyl disulfide (DADS), a primary decomposition product of allicin.
When the sclerotia germinates, it develops a mycelium which becomes
susceptible to hyperparasitism and lysis. In the absence of a host, the fungus
dies without reproducing. Two applications of the synthetic germination
stimulant DADS, but not DPDS or garlic oil in consecutive years resulted i9n
significant reduction of onion infection on organic.
Soils should be treated when the soil temperatures are between 10 and
20
and will remain remain in this range for approximately 3 months with
good uniform spread of the stimulant.
Biologic control of the invasive chilli thirps, Scirtothrips
dorsalis
[1311]
The invasive chilli thrips, Scirtothrips dorsalis Hood poses a significant risk
to many food and ornamental crops in the Caribbean, Florida and Texas. It
feeds on leaves, turns them brown, kills new growth and attacks up to 150
crops, including peppers, strawberries, tomatoes, peanuts, cotton and a
variety of ornamentals.
Arthurs and colleagues tested two species of phytoseiid mites Neoseiulus
cucumeris and Amblyseius swirskii as predators of Scirtothrips dorsalis.
Biologic control may avoid chilli thirps to become resistant to
insecticides. According to the authors, the mites were effective in reduction
of the number of thrips, whereas Amblyseius swirskii was the most effective
compared with Neoseiulus cucumeris. A good foto documentation may be found at
http://www.mrec.ifas.ufl.edu/lso/thripslinks.htm.
[1312]
According to Coleman and Seybold the Southern California beetle Agrilus
coxalis is a wood-boring beetle. It is also known as goldspotted oak borer.
Larval feeding kills patches and strips of the phloem and cambium resulting in
crown die back followed by mortality.
Oaks (Quercus spp.) are the dominant tree species in Southern
California, but 67% of the trees were attacked by the beetle. Their reduction of oaks by the
pest will reduce wildlife diversity and increase fire danger. The trees are
getting more succeptible to the beetle because of the stress imposed by drought
and climate change.
[1313] [1314]
According to Koch and Smith 2009 the avocado production may be seriously hit by
the Redbay Ambrosia beetle (Xyleborus glabratus Eichhoff), mowing to the south of the USA.
Lauret wilt is a disease of redbay and sassafras (Sassafras albidum) trees
caused by the fungus Raffaelae lauricola. The fungus
lives in association with the Ambrosia beetle (Xyleborus glabratus) which
bores into the sapwood of redbay and sassafras (Sassafras albidum) trees.
The female beetle carries spores of the fungus Raffaelea lauricola. The
beetles and their larvae feed from the fungus, which germinates in the sapwood
and cause tree death, a plant disease called laurel. Avocado trees (Persea
americana) and other Lauraceae trees of the coastal Florida, Georgia, and
South Carolina are endangered.
The authors stress that Raffaelea lauricola differs from other Raffaelea
species in its DNA sequence and spore sizes and grows faster than similar
fungi. It also harms shrubs like the pondberry (Lindera melissifolia)
[1315] and pondspice(Litsea aestivalis, L.)
[1316].
Some authors suggest the use of fungicides to protect avocado trees other opt
to isolate and remove any infected trees as soon as they begin to show signs of
wilting.
Disruption of human caused, long-distance dispersal, however, are seen by Koch
and Smith, as the most effective measure to control the spread of the beetle
and fungus.
California Bay Laurel is also a tree which was found succeptible to the fungus
Raffaelae lauiricola. Another fungus which can infect the California laurel is
oomycete plant pathogen Phytophthora ramorum causing a disease known as Sudden
Oak Death. The pathogen will take advantage of wounding, but it is not necessary
for infection to occur [1317].
The Mediterranean fruit fly Ceratitis capitata attacks fruits, vegetables and nuts.
The female Mediterranean fly mates once in her life span depositing the sperm
in the female sperm-storing organ, the spermatheca. The female produces 250 -
1,200 eggs which can be fertilized with the stored sperms from the spermatheca.
The fertilized eggs are deposited beneath the outer surface of fruit and
vegetables hatching into maggots which then feed on the pulp of the fruit or
vegetable spoiling them. Matured maggots drop to the ground, form pupae and
eventually emerge as new flies, completing the life cycle.
The fly originated in West Africa from where it spread out to North and South
Africa. As the eggs are hidden under the skin of fruits the fly can easily be
exported to all parts of the world. The fly is now being found in Europe,
Middle East, Australia and South America.
Key program of USA against the Mediterranean fruit fly
In California the
Mediterranean fruit fly was seen for the first time in 1975. USA has a key
program against the fruit fly distributing traps with
trimedlure as bait for the fly.
Ug99 has also known as TTKS is a race of black stem rust (Puccinia graminis
tritici) which has jumped from eastern Africa and is now
infecting wheat in Yemen in the Arabian Peninsula.
According to the Food and Agriculture Organization of the United Nations
(FAO), countries in the predicted, immediate pathway grow more than 65 million
hectares of wheat, accounting for 25 percent of the global wheat harvest.
[1318]
According to Ravi P. Singh and colleagues 2006 the stem or black rust, caused by
Puccinia graminis tritici is of high importance because most wheat cultivars
currently grown in its likely migration path, i.e. to North Africa through
Arabian Peninsula and then to Middle East and Asia, are highly susceptible to
this race. The long-term strategy should focus on rebuilding the "Sr2-complex" to
achieve long-term durability. A Global Rust Initiative has been launched to monitor the further migration of this race.
[1319]
[1320]
Dr Lesley Boyd at the John Innes Centre identifies the genetic resistance to
stem rust. Stem rust has the potential to wipe out 40-70% of wheat yields and
has already caused a painful spike in wheat prices. The Centre says that for
farmers who cannot afford to use expensive fungicides, resistance is the only
defence.
The centre is also focused on food security for poor rural population developin
feasible solutions for crop pests:
Armyworm
(Pseudaletia unipuncta Haworth) may ne controlled with the use of a naturally occurring virus as a
biological pesticide. The African armyworm is an insect which feeds on cereal crops.
Witchweed (Striga asiatica) is a parasitic
plant that attacks some of the most important crops such as corn, sorghum, sugar
cane, and rice, reducing yields drastically. Witchweed rob nutrients and
moisture by tapping directly into the host's root system. Consequently, the host
spends energy supporting witchweed growth at its own expense. The Centre is
developing resistant crops.
Pearl millet provides
food security for half a billion people in Africa and Asia. The researchers are
improving pearl millet's genetic tolerance to drought caused by climate change.
Root-knot
nematodes are microscopic worms that feed on plant
roots, stunting their growth. The researchers are looking for a natural soil
fungus to destroy the worms' eggs.
Reducing arsenic levels in rice:
Irrigation with arsenic contaminated groundwater,
pollution resulting from mining and the use of municipal solid waste as
fertilizer causes rice to have high content of toxic arsenic. Researchers are
searching for types of rice which have lower take-up levels of inorganic arsenic.
- Climate and weather: Frost,heat, excessive rain, hail shower, snow, light and storm.
- Composition of the soil: The soil may be to compact, carry insufficient amount of water. It may have insufficient oxygen,insufficient amount of nutrients.It may have excessive manganese and aluminum.
- Environment poisons:
Hop mildew was introduced in North America in 1890 coming from Europe and Asia. Hop mildew destroyed the plantations of hop of east and middle west of USA. The mildew mould was found all over the country.
Asparagus rust reached America 1912.
Quarantine of plants and seeds being imported are an important measure against uncontrolled spread of plant diseases.
Silage
[1333]
To avoid moulds and resulting aflatoxins in hay silage and forage as well as silage grains and feeds liquid concentrates of fermentation extracts of Lactobacillus acidophilus, lactis in the pre-bud stage of growth may be added. Alfalfa hay can thus be baled with 18 to 23% moisture.
1 ton square bales hay had the best results on proteins when obtained
at 20% moisture.
Most frequent hazards to trees
[1782]
Beetles:
Beetles attack deciduous trees and coniferous forests.If they fed on leaves only the damage is not great, but some beetles such as bark beetles can destroy large parts of the plant beneath the bark. Other beetles transmit virus diseases.
Rhychaenus fragilis: Their larva undermine the leaves of the red beech
and copper beech. the leaves turn out brown.
Elm sapwood beetle (Scolytus scolytus): is known to attack European elms. In America Elms are threatened by Hylurgopinus rufipes.
Big brown weevil (Hylobius abietis): This beetle gnaws round holes in the bark of young conifers causing their death.
Butterflies
If numerous butterflies are present complete defoliation of the growing ends may happen. Of importance are
Sackbeetle (Thyridopteryx ephemeraeformis): Male species with wings are harmless.Female species are wingless and live in a sack spun with leaves and leavestalks of USA shrubs and trees. They can cause defoliation of young trees.
Moonbird (Phalera bucephala): Larvae can cause complete defoliation at various deciduous trees.
Tamarack moth (Coleophora laricella): The larvae hollow out the needles of tamarack.
Western tent caterpillar (Malacosoma pluvialis): Their larvae live on hardwood trees of the Pacific coast of USA, inside of cocoons and nourish themselves with the young shoots of the plants.
Sawflies
Adult species are not harmful, but their larvae destroy leaves and needles heading to complete defoliation.
Larch sawfly (Pristiphora erichsonii): The larvae nourish from larch needles.causing destructive defoliation.
Willow sawfly (Pontania vesicator): It forms blister-like galls between the midrib and leave edge of willow trees. In these galls larvae develop.
Plant louse
They are small insects which may have wings or are wingless. attacking deciduous trees and coniferous plants.
Schizoneura lanuginosa: It sucks on elm leaves . not regular galls are formed.
Byrsocrypta ulmi (Byrsocrypta ulmi:) produces similar lesions as the galls of Schizoneura, but they are club formed.
Pemphigus bursarius: It attacks poplars deforming the petioles with galls.
Sitka spruce Picea sichensis: It feeds on the vascular system of spruce.
Scale insect: Scale insects are generally covered by a waxlike protective cover. Only female species produce damage. They attack deciduous trees and coniferous plants.and fruits. Leaves and needles may die.
Common scale insects are :
San-José-scale Insect, Pernicious scale Diaspidiotus (Quadraspidiotus)
perniciosus
sucks on
leaves and fruits of apple-, plums- and peach trees.
The insect is small. it introduces its mouthpieces in the plant and feeds from the liquids. It secrets a white waxi material.
The University of California maintains the Statewide Integrated Pest Management Program, stressing that San Jose Scale has many natural enemies which, however, may be disrupted by broad-spectrum insecticides. Not using broad-spectrum sprays for 2 or 3 years may thus solve San Jose scale problems. [1783]
Beech scale (Cryptococcus fagi): It is a sap feeding insect which together with at least two Nectria fungi causes beech bark disease.
The American Beech (Fagus grandifolia) may be infested with the beech scale (Cryptococcus fagisuga Lind= fagi Baer).The tiny insects attack trunk and branches of the trees suckling sap of the inner bark.White wax covers the bodies of the scale so trees seem to be covered by white wool. Very small wounds caused by the scale enable the Nectria fungus to penetrate the tree killing areas of woody tissue. The tree will be girdled and die. Some infected trees will break off in heavy winds which is called "beech snap".
The scale insect is tiny. It feeds on sap of the inner bark of the tree trunk and branches of American and European beech trees (Fagus sylvatica). The body of the scale is covered by a white wax which gives a look of white wool covering heavy infected parts of the tree. The scale insect causes small wounds and injuries which enables the Nectria fungus(Nectria galligen, Nectria coccinea var.faginata, Nectria ochroleuca) to penetrate the deeper tissues of the tree. leading to widespread damages.
The wind may transport scale insects and fungal spores, spreading the disease.
The scale insect and the Nectria fungi can be transported from tree to tree in wind. The Nectria fungi species which are associated to beech bark disease are: Nectria galligena , Nectria coccinea var.faginataand Nectria ochroleuca.Beech scale alone does not kill the trees but after 3 to 6 years an invasion of Nectria fungi takes place which leads to the destruction of the plant.
Oistershell scale, Mussel scale (Lepidosaphes ulmi:) It feeds from the liquid of plants such as olive and apple trees causing incrustations on branches, twigs and fruits.It also leads to the splitting of the bark.
Anthracnose fungus (Colletotrichum sp.): is a disease of plantations of coffee, cashew, melons,citric fruits (Colletotrichum gloeosporioides) but also trees are affected, such as willow trees and poplar trees.Humidity accelerates the growth of the fungus.
Also economical important is Colletitrichum lindemuthianum (Sace and Magn.)which attacks black beans important food in Brazil.
Armillaria mellea: Is a root disease which is a frequent cause of decay of trees in garden and in free nature. It survives as mycelium in the roots and wood of dead trees. The mushrooms of Armillaria grow in clusters at the base of dead or dying tree-trunks or near infected roots.
Plantations of coffee can be infested by Armillaria and Rosselinea spp. which has remained in roots and wood of trees of preceding forest.
Fruit tree red spider mite: Mites are spider like organisms which nourish from plant sap.
Economical important mite is the Fruit tree red mite Metatetranychus ulmi. it feeds by sucking the underside of leaves of vine and fruit trees like apple, pear, cherry-trees. The leaves turn brown and dry.
Bursaphelenchus xylophilus
It is a nemathode which attacks pines. Its habitat is the southwest Asia and is present in USA, Japan China and Scandinavia.
The nemathode is vectored from one pine to another by cerambycid loghorn beetles, also known as sawyers of the genus Monochamus. It can destroy 50 to 70 years old trees within few years.
In Germany,Saxony living nematodes Bursaphelenchus xylophilus were found for the first time among pallet wood of Chinese origin. As wood for pallets are of poor quality of dead trees are used pallets turn out to become a way of spread pests all over the world.
Diseases of potatoes
Tuber diseases:
Pink rot: is caused by the fungus Phytophthora erythroseptica which is soil-borne. Pink rot can be detected by a smell of ammonia prior of visual symptoms.
Phytium leak is caused by the fungi Phytium debaryanum and Phytium ultimum.Also known as water rot is caused by the fungus Phytium spp. living in the soil. The fungus invades the tubers through wounds made during harvest. It causes internal wet spongy rot with hollow cavities leaving behind only the tuber shells as thin paper skins.
Avoid overwatering near harvest. Avoid unnecessary damage to the tubers during harvest.
Fusariun dry rot:It is a postharvest disease of potatoes. It is caused by several soilborne fungus Fusarium. Infected tubers have wrinkled, sunken, brown to black lesions. The Fusarium fungi are common in soil and decaying plants as resistant spores. After low-temperature storage, internal tissues become firm and dry or even powdery.
Potato bacterial ring rot: is caused by Clavibacter michiganensis subsp. sepedonicus producing yellow areas which start on leave margins later turning brown. The leaves look like being burned.
Brown necrosis of the tubers are formed from the middle of the tuber, progressing to surface, leaving sometimes only hollow shells.
Rhizoctonia Canker: It is a disease of potatoes caused by the fungus Rhizoctonia solani. It is known as black scurf Hard black bodies called sclerotia are formed on the surface of the tubers. Delayed budding is caused by an attack of the buds by the fungus. Misshappen stems and weak plants with brown cankers at the base and belowground portions of the stem.
Silver scurf: Is a potato disease caused by the fungus Helmithosporium solani. It causes a metallic discoloration of the epiderma and causes weight loss during storage due to increased water loss of the tubers. Shrinking and flabbiness affects peeling of the tubers reducing consumer acceptance and rejection. It is a seed-borne disease.
Spongospora, Powdery Scale Is a disease of potatoes caused by Spongospora subterranea which can be the vector of the mop-top furovirus.
Net necrosis:
Foliar diseases
Early blight: Potato early blight is caused
by the fungus Alternaria solani. It is a disease of
stressed and senescing plants.
Lesions of the leaves are circular with a target look. They turn out yellow and drop. Tubers develop dry rot lesions which appear sunken.
Infection is possible during wet and warm weather conditions (dew, rain or sprinkler irrigation). Tubers can be contaminated by lifting them through the surface soil.
Early blight can be reduced with with optimum growing conditions like fertilization,irrigation and other pest controls in order to strengthen the plants. Fungicide application is recommended only when the plants become diseased in a very early stage so the damage will be considerable.
Potato late blight[1358]
Potato blight is caused by Phytophthora infestans a fungus-like organism whose sporangia are dispersed by wind. To avoid damage
caused by blight the potato farmers watch weather forecasts for the
climatic conditions which favor the spread of the disease. Spraying
fungicides may be unnecessary when blight spores are not present in
the air current. More efforts are being done to control spore flight
with air sampler in connection with flow cytometer. Particles collected
by the sampler are stained and analyzed in the cytometer using laser
light. Airborne potato blight spores are identified and counted
against a background of other fungal spores, pollen and inert
particles. This system is being developed by Dr. Gareth Griffith of
the Institute of Biological Sciences at the University of Wales,
Aberystwyth.
The forecast of the potato blight disease which has caused the Irish
Potato Famine, 1845-1847 leading to the death of 1 million people
could be improved using data of the climatic forecast ( suitable
conditions for pathogen growth) and detection of the sporangia in air (inoculum).
With the help of these data the decision to spray the crops could
could reduce excessive fungicides.
Potato late blight is caused by the fungus Phytophthora
infestans and is the most important potato
disease. Specially the US-8 genotype is strongly resistant to the fungicide
mefenoxam and is together with the genotype US-11 very aggressive.
The spores of the fungi are carried by wind or other infection ways from one
field to another. Once the fungi is established in the plant no chemical
fungicide can kill it. Prevention is therefore the best way to prevent great
damage. Fungicides must always be applied before the crop shows any signs of
infection. The fungus hibernates in infected potato tubers as mycelium.New
sprouts of the mycelium invades the cortical tissue of the tubers.Reaching the
aerial part of the plant sporangiosphores will be created and which emerge
through the stomata of leaves or stems.The sporangia which are then produced
can infect other wet plants by means of wind and rain. Infection of tubers may
not be seen during harvest, but it will go on during storage.
The sporangia can also spread on soil and tubers near the surface.
Prevention of potato late blight depends
on the forecast of temperature and humidity of the specific region
When the relative humidity is below 80% the sporangia will lose its ability to
germinate in 3 to 6 hours. Free moisture or dew makes germination possible.Best
conditions for growth of the fungus is 100% of relative humidity.
Preventive application of fungicides are necessary if the environmental
conditions are favorable for the disease. Mefenoxam is not recommended because
Phytophthora infestans is resistant to it. If there is an infection of late
blight the vines should be dead 2 to 3 weeks before harvest to avoid
contamination of the tubers, as Phytophthora infestans does not survive for
long in dead foliage.
Copper free compounds had either no or limited effects on blight
compared with copper fungicides [1359]
The EU project leaded by Professor Carlo Leifert aims the development of
management of late blight in EU organic potato production. In this project it
is being notet that there is a widespread view that a copper fungicide ban
will have serious consequences for organic potato production unless effective
alternatives are available.
Some conclusions of this project were:
Extracts of manure-based composts gave control of blight in potato leaf assays
but not in the field. However, use of an adjuvant in combination with an
autoclaved compost extract gave improved control and slightly higher yields in
an experiment in 2003. Some micro-organisms, plant extracts and existing
products showed promising effects on blight control. Efficacy of a range of
commercial and novel anti-fungal compounds was unaffected by dose rate or
formulation. Copper free compounds had either no or limited effects on blight
compared with standard copper fungicides at normal rates but low doses of
copper products were almost as effective.
Net necrosis and Potato leaf roll virus: Net necrosis is caused by the potato leaf
roll virus (PLRV). It is a damage of the cells of the vascular tissue.of the
tuber causing specific symptoms.
The virus can be spread by means of various aphid species such as the green
peach aphid which can be killed with carbamate
insecticides. Mechanical contact does not cause a transmission of the virus
from plant to plant. it occurs only with a vector such as the aphids.
[2116]
According to Dr Richard Harrington aphids, such as the peach-potato aphid
(Myzus persicae) are found flying around almost four weeks earlier, and
their number in spring and early summer is increased when crops are
particularly vulnerable to damage.
Aphids extract large amounts of sap, weakening the host plant, and spread
plant viruses. Aphids excrete very sticky honeydew, which can encourage the
growth of moulds causing further weakening and attract ants which live in
symbiosis with the aphids.
Up to date news on the distribution and abundance of pest aphids at a regional
scale in UK based on data from a network of sixteen suction traps are
provided by the Centre for Bioenergy and Climate Change Department of Plant
and Invertebrate Ecology, Rothamsted Research. These long-term data on the
seasonal appearance of flying aphids not only show that there are already
noticeable changes in the UK climate, but they also provide the knowledge
which will help to mitigate the consequences. [2117]
Richard Harrington and colleagues 2007 suggested the possible value of aphids in
predicting responses to environmental changes. Aphids have a short generation
time and low developmental threshold temperatures and respond particularly
strongly to environmental changes. Forty years daily survey data of aphids have
been collected throughout the European Network "EXAMINE".
[2118]
[2119]
Phenology is the study of the annual cycles of plant and animals and how they respond to seasonal changes
in their environment.
The uses of phrenology can be used in IPM:
- Correlation with insect emergence and pest control.
- Correlation with crop planting dates
- "Trap cropping" planting small plots at the beginning and end of a growing season to attract and concentrate pests which can be killed by selective insecticides
- Designing bee forage plantings
- Designing orchards for pollination and ripening sequence
Desertification[2120]
On the occasion of the World Day to Combat Desertification to be celebrated on June 17, 21006, worldwide farmers of the International Federation of Agricultural Producers presented a message, highlighting the essential role of farmers to combat desertification and their commitment to join efforts along with the international community and other relevant stakeholders to be more effective in this endeavour:
In a new policy statement, IFAP calls for increased investment in agriculture to turn dryland areas into economic ones through: investments in family farming and local food security which are the engines of economic growth; looking at all the assets of rural development; as well as development of people centered and rights based approaches to rural development.
Natural resources such as fertile topsoil, organic matter, plant cover and healthy crops are the most severely affected by desertification.
The United Nations Convention to Combat Desertification (UNCCD) presents a sustainable development and poverty reduction instrument. Unfortunately lack of investment for implementing the Convention due to a lack of political will and commitment hinders its activities. [2145]
Almost one-quarter of the earths land surface are defined as 'desert' , being home for over 500 million people. Degradation of fragile drylands are progressing due to overgrazing, overuse of land climate variations deforestation and poor irrigation methods.
Most of the 12 desert regions have a rainfall forecast of 10 to 20 per cent lower by the end of the century. Very threatened by drought are Chad, Iraq, Niger and Syria.
The Brazilian Census Bureau (IBGE) estimates an harvest of 59.2 million tonnes of soybeans in 2005-06, up from 51.1 million tonnes in 2004-05. Some crop losses due to dry weather in the previous season were reported.
Asian rust is another factor that could endanger some part of the Brazilian crop. Small and medium-sized farmers cannot pay the spray if rust attacks. Asian soybean rust was first found in Brazil in 2002 and has since spread to Brazil's major soy regions.
Extreme heat and drought in much of the Midwest in 2005 limited the spread of soybean rust to the southern United States (central Florida, reaching Kentucky and Texas ).X. B. Yang of the Department of Plant Pathology of the Iowa State University the disease developed slower in kudzu plants in southern states compared with those in South America. This might have been due to the biology of the U.S. Kudzu soy plant. However, the disease is still a serious threat to all U.S. soybean growing areas. [2147]
Asian soybean rust: It is a fungal disease caused by Phakopsora pachyrhizi. It can defoliate plants and reduce pod set, pod fill, seed quality and yield.
Similar looking diseases Diseases which are similar looking to asian soybean rust are:
- Bacterial Blight Pseudomonas syringae pv glycinea
- Bacterial PustuleXanthomonas campestris pv. glycines
- Cercospora Blight caused by the fungus Cercospora kikuchii
- Frogeye Leaf Spot Cercospora sojina
- Downy Mildew fungus Peronospora manshurica
- Brown Spot is a fungal disease caused by Septoria glycines
[2146]
The European Commission in a statement comments heat and drought in summer 2006 as follows:
"Frequent and persistent heat waves associated with dry conditions characterised the whole month of July. At the same time, the drought and the heat stress phenomena moved northward through the continent affecting particularly those areas where the winter crops were still at their sensitive stage (ripening/maturity),
Both in southern and in northern Europe, the spring-summer crops, in full vegetative to flowering phase, were suffering from the above-mentioned conditions. All this also had an impact on water reservoirs, reducing the irrigation resources mainly for grain maize, sugar beet and potatoes.
Severe
drought in German corn
Summer 2006 a severe drought makes corn leaves acquire a curly formate.
[2148] [2149]
Gregory Crutsinger and colleagues from the University of Tennessee in Knoxville found that increasing population genotypic diversity in a dominant old-field plant species, goldenrod (Solidago altissima), determined arthropod diversity and community structure and increased aboveground net primary productivity (ANPP), such as the insect diversity.
Goldenrod
(Solidago altissima)
The scientists counted and identified every insect on every plant. Crutsinger found that plants from plots that had the most genetic diversity ,12 genotypes, were bigger and contained not only the most insects but also the most species of insects. than plots with a single plant genotype.
The results of the study suggests that the goldenrods in the genetically diverse plots had provided better quality resources to the insects, with a resulting positive impact on the plants too.
Crutzinger thinks that tiny differences in plant characteristics, from leaf shape to stem thickness, might have promoted a wider diversity of pests and pollinators and spread out their effects over the plot, so that some plants are really nailed by insects and some are barely touched at all, The plants might also have picked nutrients out of the soil differently from each other, helping them make best use of the resources available.
Crutsinger concludes that the findings are significant for conservation biology and stresses the importance of genetic diversity within the crops.
Similar results had been reported by Youyong Zhu [2150]. He mixed a disease-susceptible with a disease-resistant variety of rice. Growing the two together boosted yields.
Youyong Zhu concluded that crop heterogeneity is a possible solution to the vulnerability of monocultured crops to disease. Both theory and observation indicate that genetic heterogeneity provides greater disease suppression when used over large areas.
[2151]
Insect resistance management (IRM) is the term used to describe practices aimed at reducing the potential for insect pests to become resistant to a pesticide. Bt IRM is of great importance because of the threat insect resistance poses to the future use of Bt plant-pesticides and Bt technology as a whole. Specific IRM strategies, such as the high dose/structured refuge strategy, will mitigate insect resistance to specific Bt proteins produced in corn, cotton, and potatoes.
Academic scientists, public interest groups, organic and other farmers have expressed concern that the widespread planting of these genetically transformed plants will hasten the development of resistance to pesticidal Bt endotoxins. Effective insect resistance management can reduce the risk of resistance development.
The insect resistance management section provides EPA's scientific assessment of various Bt plant-pesticide IRM strategies by reviewing the data and information available to the Agency. The Agency will use this assessment, the report of the FIFRA SAP meeting on October 18, 2000, and all public comments in its development of its risk management decisions for Bt plant- pesticides. The whole document can be downloaded at http://www.epa.gov/oscpmont/sap/meetings/2000/october/brad4_irm.pdf
Insect pest discussed in the EPA insect resistance management documet are:
| Common Name |
Scientific Name |
Crop |
| Black Cutworm |
Agrotis ipsilon (Hufnagel) |
corn |
| Cotton Bollworm |
Helicoverpa zea (Boddie) |
cotton |
| Corn Ear Worm |
Helicoverpa zea (Boddie) |
corn |
| Colorado Potato Beetle |
Leptinotarsa decemlineata (Say) |
potato |
| Common Stalk Borer |
Papaipema nebris (Guen.) |
corn |
| European Corn Borer |
Ostrinia nubilalis (Huebner) |
corn |
| Fall Armyworm |
Spodoptera frugiperda (J. E. Smith) |
corn |
| Pink Bollworm |
Pectinophora gossypiella (Saunders) |
cotton |
| Southern Corn Stalk Borer |
Diatraea crambidoides (Grote) |
corn |
| Southwestern Corn Borer |
Diatraea grandiosella (Dyar) |
corn |
| Tobacco Budworm |
Heliothis virescens (Fabricius) |
cotton |
Resistance management strategy [2151]
The 1998 Science Advisory Panel Subpanel agreed with EPA that an appropriate
resistance management strategy is necessary to mitigate the development of
insect resistance to Bt proteins expressed in transgenic crop plants.
The Subpanel recognized that resistance management programs should be based on
the use of both a high dose and structured refuges designed to provide
sufficient numbers of susceptible adult insects. The 1998 SAP also noted that
insect resistance management strategies should be sustainable and to the extent
possible, strongly consider grower acceptance and logistical feasibility.
High dose [2151]
The Subpanel defined a high dose as 25 times the amount of Bt delta-endotoxin
necessary to kill susceptible individuals. The Agency has adopted this
definition of high dose. A Bt plant-pesticide could be considered to provide a
high dose if verified by at least two of the following five approaches:
1) Serial dilution bioassay with artificial diet containing lyophilized tissues
of Bt plants using tissues from non-Bt plants as controls;
2) Bioassays using plant lines with expression levels approximately 25-fold
lower than the commercial cultivar determined by quantitative ELISA or some
more reliable technique;
3) Survey large numbers of commercial plants in the field to make sure that the
cultivar is at the LD99.9 or higher to assure that 95% of heterozygotes would
be killed (see Andow and Hutchison, 1998);
4) Similar to #3 above, but would use controlled infestation with a laboratory
strain of the pest that had an LD50 value similar to field strains; and 5)
Determine if a later larval instar of the targeted pest could be found with an
LD50 that was about 25-fold higher than that of the neonate larvae. If so, the
stage could be tested on the Bt crop plants to determine if 95% or more of the
later stage larvae were killed.
Effective IRM is still possible even if the transformed plant does not express
the Bt protein at a high dose. If the Bt plant is non-high dose, the IRM plan
could include increased refuge size, increased scouting and monitoring, and/or
prohibition of sales of non-high dose products in certain areas.
Structured refuge [2151]
A structured refuge is a non-Bt portion of a grower's field or set of fields
that provides for the production of susceptible insects that may randomly mate
with resistant insects that may emerge from Bt fields and dilute resistance.
The size, placement, and management of the refuge is critical to the success of
the high dose/structured refuge strategy to mitigate insect resistance to the
Bt proteins produced in corn, cotton, and potatoes. The 1998 Subpanel defined
structured refuges to "include all suitable non-Bt host plants for a targeted
pest that are planted and managed by people.
These refuges could be planted to offer refuges at the same time when the Bt
crops are available to the pests or at times when the Bt crops are not
available." The Subpanel suggested that a production of 500 susceptible adults
in the refuge that move into the transgenic fields for every adult in the
transgenic crop area (assuming a resistance allele frequency of 5 x 10-2) would
be a suitable goal. The placement and size of the structured refuge employed
should be based on the current understanding of the pest biology data and the
technology. The SAP also recognized that refuges should be based on regional
pest control issues.
Insect resistant management imposed on registered Bt plant-pesticides
[2151]
To address the very real concern of insect resistance to Bt proteins, EPA has
imposed IRM requirements on registered Bt plant-pesticides. Sound IRM will
prolong the life of Bt pesticides and universal adherence to the plans is to
the advantage of growers, producers, researchers, and the American public.
EPA's strategy to address insect resistance is two-fold:
1) mitigate anysignificant potential for pest resistance development in the
field by instituting IRM plans, and
2) better understand the mechanisms behind pest resistance. Beginning with the
first Bt plant-pesticide registration, the Agency has taken steps to manage
insect resistance to Bt with IRM plans being an important part of the
regulatory decision. The Agency identified (later confirmed by the 1995 SAP)
seven elements that should be addressed in a Bt plant-pesticide resistance
management plan:
1) knowledge of pest biology and ecology,
2) appropriate dose expression strategy,
3) appropriate refuge,
4) resistance monitoring and aremedial action plan should resistance occur,
5) employment of integrated pest management (IPM),
6) communication and education strategies on use of the product, and
7) development of alternative modes of action.
Developing an IRM plan [2151]
Key to developing an effective IRM plan is an understanding of the pest(s)
biology, the dose ofthe protein expressed in the various plant tissues, and the
size and placement of the refuge (a portion of the total acreage using non-Bt
seed). It is believed that planting a refuge will delay the development of
insect resistance by maintaining insect susceptibility. In addition to a
structured refuge, IRM plans include additional field research, resistance
monitoring for the development of resistance (and increased insect tolerance of
the protein), grower education, a remedial action plan in case resistance is
identified, annual reporting and communication. IRM plans will change as more
scientific data become available. EPA, has in fact, changed IRM plans as new
data has become available.
A summary of the Agency's risk assessment of insect resistance development and
insect resistance management plans to mitigate resistance is provided below for
Bt corn, Bt cotton, and Bt potato products. The detailed Agency risk
assessments of insect resistance management are found in the following
memoranda: A. Reynolds and R. Rose (OPP/BPPD) to M. Mendelsohn (OPP/BPPD),
dated September 11, 2000; S. Matten (OPP/BPPD) to W. Nelson (OPP/BPPD), dated
July 10, 2000; S. Matten (OPP/BPPD) to W. Nelson (OPP/BPPD), dated September
11, 2000; and S. Matten (OPP/BPPD) to W. Nelson and L. Hollis (OPP/BPPD), dated
July 5, 2000.
[2152]
The wasp Trichogramma brassicae Bezdenko, Hymenoptera Trichogrammatidae, is a a
parasitoid of Lepidopteran eggs. This activity of T. brassicae is used to control
the the European corn borer and is now available to fight the Indian meal
moths (Plodia interpunctella) .
[2152]
According to the Colorado State University Extension adult insects are small and
have a broad, grayish band on their bronze-coloured wings. Immature Indian meal
moths develope on dried food product, such as grain, dried fruits, nuts,
crackers, powdered milk, bird seeds and dog food. Household infestations
originate from purchase of infested foods, but come also from moths moving in
from outdoors. Small, white worms and webbing indicate infested foods which must
be discarded. To avoid losses the author suggests to place the food package in
the freezer for several days, microwaving or warming up to 55
for three
hours, to kill insect eggs and larvae.
[2156]
Some biologic companies such as AMW, Germany, sell cards with attached eggs of
moths which are parasited with Trichogramma brassicae or T. evanescens wasps
as pupae. These cards may be placed in the infested storage compartment. After
some days the pupae of Trichogramma brassicae hatch. Females search for eggs of
the moth and lay eggs within them. The resulting larvae eat up the content of
the infested egg of the moth.
[2153]
According to the Agricultural Research Service (ARS) whiteflies are found
throughout the tropics and subtropics, but can be troublesome in greenhouses
and other growing environments as well. Both immature and adult stages ingest
plant sap and cause damage directly, by feeding and transmitting plant
viruses, or indirectly, by excreting a sticky substance called honeydew onto
leaves and fruit.
Sooty mold fungi colonize the contaminated surfaces, further interfering with
photosynthesis and ultimately resulting in reduced quality of fruit and fiber. In
addition to ornamentals, whiteflies attack cassava, cotton, sweet potato, legumes
and many other vegetables grown in mixed or annual cropping systems.
The USDA maintains an online guide on whiteflies. The importance of crop
hygiene, pre- and post-planting practices, insecticide recommendations and
the need to control whiteflies early, before they spread to neighbouring
fields is stressed.
Proper use of insecticides is important for whitefly management, particularly
with respect to avoiding development of insecticide resistance in whiteflies.
Insecticide misuse may result in silverleaf whitefly populations that cannot
be controlled. The online guide stresses that the Q-biotype whitefly is
already resistant to a number of products commonly used. Chemical overspray
could easily lead to B-biotype resistance. Biotyping of whiteflies should be
made to decide between the strategy to be applied. Samples of white flies may
be sent to the given addresses which will see if it is the Q or the B biotype.
It is recommended that insecticides be rotated between chemical classes and
should be applied a minimum of two times, at a five- to seven-day interval, to
allow for egg hatch between applications and ensure that adults, nymphs and
newly hatched individuals are all killed.
The USDA Agricultural Research Service (ARS) online guide can be accessed at:
http://www.mrec.ifas.ufl.edu/LSO/bemisia/bemisia.htm
The silverleaf whitefly, Bemisia argentifolii (previously known as B. tabaci
biotype B), injures plants directly by feeding and indirectly by transmitting
plant viruses. The plants become a yellow, mottled look and eventually die.
White flies have a natural resistance to pesticides. Repeated applications are
needed resulting in hazard for environment, animal life or humans.
Therefore biologic by natural enemies of the fly was studied by Cabanillas
which proposed in 2001, the fungus Isaria propawskii. This fungus kills larval
and adult stages of silverleaf whitefly. Isaria propawskii include
establishment itself in a semiarid region where temperatures can reach 42°C
and persists, even in the absence of insect hosts. It is also highly pathogen
to the glassy-winged sharpshooter, Homalodisca vitripennis (previously known
as H. coagulata) [2154].
The female Eretmocerus mundus wasps may become another biocontrol of whiteflies.
It produces marking pheromones, which are specialized lipids for marking
whitefly nymphs they have chosen as egg hosts. This makes other wasps to choose
another egg to lay their eggs. This avoids double-parasitizing turning the
whitefly control very effective. The pheromones used by the wasps as markers were
found to b e C31 and C33 dimethylalkanes [2155].
[2156] [2157]
[2158]
This biologic control was used to reduce the infestation of corn fields with
the corn stem borer. Trichogramma spp are sensitive to insecticides such as pyrethroids.
The correct timing is necessary, fresh infected eggs are therefore provided in
an interval of two to three weeks. The chemical corporation BASF made
researches with Trichogramma spp to control the corn stem borer, but abandoned
the project in face of an enormous personal investment. The company turned
therefore to support the genetic modified Bt-Corn which produces a protein
which is toxic to the larvae of the corn stem borer.
A renaissance of the biologic method using cards with moth eggs infested with
Trichogramma brassicae to protect extensive fields of corn is triggered by the
concerns related to GM safety.
Some companies such as Sautter & Stepper. Are specialised of a variety of
biologic agents to control pests without chemicals.
With global tranportation of all kinds of goods, eggs, larvae and insects are
being introduced in regions where these pests were unknown before. One pest is
the box-tree pyralid (Glyphodes perspectalis), which migrated from East Asia to
Europe causing damages in market garden. Its natural enemy is being surged for.
Citrus canker:USDA APHIS study not supported by scientifically sound
evidence.
The USDA APHIS evaluation of asymptomatic citrus fruit, (Citrus spp.) as a
pathway for the introduction of citrus canker disease (Xanthomonas axonopodis
pv. Citri) concludes that it is highly
unlikely that citrus canker could be introduced on asymptomatic, commercially
produced citrus fruit that has been treated with disinfectant dips and subject
to other mitigations. Even if infected fruit were to enter a canker-free area
with susceptible hosts, the establishment of citrus canker via this pathway
appears to be unlikely. [2159]
The new Plant Health (PLH) Panel of the European Food Safety Authority (EFSA)
evaluated a recent study on citrus canker disease published by the US
Agriculture Department's Animal and Plant Health Inspection Services (APHIS)
with special attention to its conclusion that citrus canker is not likely to
spread by means of citrus fruit that show no signs of the disease. The PLH
Panel concluded that key arguments in the study, and its conclusions, were not
supported by scientifically sound evidence. [2160]
Citrus canker is an economically significant plant disease caused by the
bacterium Xanthomonas axonopodis pv. citri (Xac) affecting most of the citrus
growing areas in the world, including Florida. Once established, various
control methods including spraying of copper compounds must be combined to
reduce the damage by Xac. [2161]
Rigorous phytosanitary measures have insured that some areas, including Europe,
are still free of the disease. These include the use of systems approaches. The
current systems approach for the trade of citrus fruit requires that fruit are
coming from disease-free area surrounded by a non-export buffer zone. The APHIS
document proposes to modify the systems approach so that asymptomatic fruit
coming from infected/contaminated areas are eligible for trade. [2161]
The APHIS proposal to allow fruit from contaminated groves to be traded is a
major deviation from existing phytosanitary measures. The APHIS document
analyses the five events that must occur for successful introduction and
proposes a new systems approach to prevent entry and establishment. However, no
new or additional studies are presented and the analysis of the evidence
provided in the document does not justify a change in the regulations. None of
the preventative measures in the systems approach proposed by APHIS are shown
to give effective control of Xac. Therefore, it can be concluded that, where an
initial inoculum load exists, the transmission of Xac in the scheme proposed by
APHIS is more likely than with the current systems approach.
[2161]
As tapioca starch finds growing applications in global food industry
the producing countries are highlighted: Nigeria is the largest producer of
cassava, followed by Brazil, Thailand Indonesia and Congo. Floods, droughts and
cassava mosaic virus threaten African tapioca yields, and low prices for
cassava made Thailand farmers change from cassava to maize and sugar cane
because of low prices of cassava. To counter this,Thai government plans to
launch a futures market to stabilize the price. Bacteria harm cassava such as
Phytomonas manihotis in Brazil, Bacterium
cassava in Africa and Bacterium solanacearum
in Indonesia. Insects like locusts, beetles and
ants, rats, goats and wild pigs may devastate plantations.
[2162] [2163] Ryan J.
Hayes, Krishna Subbarao and colleagues studied the disease verticillium
wilt of iceberg lettuce. The
lettuce collapses before firm nicely rounded heads are formed. The agent of
the disease is the root-rotting fungus Verticillium dahliae.
The researchers made seeds of three new parent lettuces available to
researchers and plant breeders the parent lines are meant for crossing with
consumer-ready lettuces to boost the commercially grown lettuces' resistance to
verticillium wilt.
The Verticillium dahliae fungus infects roots of vulnerable plants, moving into
leaves and causing them to discolour, then to eventually wilt and die. The
fungus can also infect and kill hundreds of other kinds of plants, including
strawberries and tomatoes.
Corky root is a disease caused by the bacterium Sphingomonas suberifaciens
which causes lettuce roots to develop ugly, yellow-to-brown lesions that harden
to a corklike texture. Corky-root-infected plants may produce stunted heads 30
to 70 percent smaller than normal.
The lettuce mosaic, is caused by a virus of the same name. It results in
stunted growth as well as unattractive mottling of leaves. Green peach aphids
can spread the virus from plant to plant.
Mou and Carolee T.Bull working at ARS are searching for corky-root-resistance
genes that are different from the one already working inside the new parent
lettuces to give lettuce additional corky-root-resistance genes.
Breeding lettuces with natural resistance remains the most environmentally
friendly, economical and sustainable option for combating the fungus and
microbes.
The authors conclude that because of the existence of resistance-breaking race
2 isolates, this resistance may not be durable. Alternatively, targeted
releases of race-1-resistant cultivars to fields with only race 1 pathogen
genotypes may extend the life of these cultivars.
Verticillium dahliae can attack tomato, eggplant, pepper,
potato,
chrysanthemum, asters, fruit trees, strawberries, raspberries, roses, alfalfa,
maple, elm and others. Damage to most fruit and vegetable crops if the
Verticillium dahliae count in soil is high. This count is made when solanaceous
crops such as potatoes, tomatoes, eggplant or peppers are to be grown.
[2164]
Lupinus polyphyllus Lindl. is a perennial ornamental belonging to the
Leguminosae family. It is grown in gardens for flower beds and borders.
Garibaldi and colleagues found the fungus Verticillium dahliae to infect up to
30% of this legumonose in Northern Italy. [2165]
Mercado-Blanco and colleagues developed a nested-polymerase chain reaction
(PCR) procedure based on the simultaneous amplification of both an ND- and a
new D-specific marker by means of duplex, nested PCR. This procedure helps to
certify pathogen-free planting material and accurate detection of defoliating
(D) and nondefoliating (ND) Verticillium dahliae pathotypes infecting olive
plant. [2166]
Jacobs and colleagues (1994) reported interspecific variation in
susceptibility to Verticillium wilt caused by Verticillium albo-atrum Reinke
and Berthier and Verticillium dahliae in redbud, and that Cercis yunnanensis
is susceptible to the disease. [2167]
Sanogo and Clary (2003) report that Verticillium dahliae recovered from the
weeds Physalis wrightii (Wright groundcherry), Anoda cristata (spurred anoda),
and Proboscidea louisianica (devil's-claw),is pathogenic to Chile pepper.
Control of Wright groundcherry, spurred anoda, and devil's-claw may be
important in the management of Verticillium dahliae in chile pepper.
[2168]
Al-Rawahi and Hancock (1998) found the fungus Pythium oligandrum to be a
parasite of Verticillium dahliae in dual culture, impeding the latter's ability
to grow and form microsclerotia. Pepper grown in soil infested with V. dahliae,
shoot and fruit weights were significantly higher in the presence of P.
oligandrum than in its absence. When soil was infested only with P.
oligandrum, fresh weights of shoots and fruits were 40 to 50% higher than when
plants were grown in its absence. The authors find that improved plant health
associated with soil treatment with P. oligandrum could be the result of
complex interactions between pathogen, host, and mycoparasite.
[2169]
Spink and Rowe (1989) evaluated Talaromyces flavus as a potential biological
control agent of Verticillium dahliae on potato, but found no significant
effect on disease development, tuber yield, or percent recovery of V. dahliae
from rhizosphere or nonrhizosphere soil at harvest. [2170]
Page and colleagues (1991) studied the loss in irrigated alfalfa (Medicago
sativa) attributable to Verticillium wilt (caused by Verticillium albo-atrum)
was determined by comparing yields of resistant and
susceptible cultivars grown
in the presence of Verticillium wilt and developed equations for making
economically sound decisions for managing alfalfa under the consederation of
losses due to Verticillium albo-atrium [2171]
Red palm weevil may pose a risk to date
production
[2172]
The red palm weevil (Rhynchophorus ferrugineus) became a risk to date palms pest lays its eggs on the bark of the
date, coconut, oil, sago and other ornamental palms . Invasion spreaded from
the Near East, the north of Africa and the European Meditarranean region. The
weevil causes a total loss of the palms and rotting of the trunk which lead to
the death of the tree. Adult females lay eggs in the crown of palm trees,
larvae then penetrate the crown and later to most parts of the upper trunk,
making tunnels of up to 1 m long. Pupation takes place in a cocoon under the
bark.
Date palm is an important crop in north African countries and ornamental palms
are widely planted as amenity trees in the whole Mediterranean area.
Phytosanitary measures taken in Israel according to Hamburger, Bitton and
Nakache 2003:
[2173]
- R. ferrugineus was declared a quarantine pest, and pheromone traps were installed.
- Mass trapping of 10-12 traps/ha was organized and to 1 trap/3 ha in non-infested areas).
- Chemical treatments of infested trees.
- Destruction of heavily infested trees.
- Preventive measures to avoid infestations (drip irrigation to maintain
trunk dry, removal of offshoots, preventive sprays on trunks).
The authors concluded that mass pheromone trapping might have played a
significant role in the suppression of red palm weevil populations in date plantations.
[2174]
The tree being damaged by the weevil exudes a foul odour. Humans can
eventually detect this smell but not soon enough to save the tree, which can
be done, if caught in time, with Golden Retriever dogs are used in a joint
Israeli-Arab project by the Shimon Peres Center for Peace, researchers. These
dogs detect the presence of the grubs in the early stages of infestation when
an injection of insecticide still may save the palm.
[2175]
Leaf-cutting ants such as Atta sexydens and Acromyrmex octospinosus live in
Argentina, the south of Brazil including the state of São Paulo. Acromymex spp
was imported in the south of the U.S.A. From Argentina by food transportation.
The ants cause heavy damage to agriculture and defoliate a tree in one night.
It is speculated that if Atta sexdens would spread into tropical Africa,
results would be devastating. As the local plants have not developed defensive
compounds against leaf cutters and Africa does not have parasites evolved to
infect them, the results for both the ecosystem and agriculture would be
devastating. [2176]
The ants live in obligate symbiosis with fungi of the genus Leucoagaricus,
which grows on leaf brought into the nest by the ants. The ants depend on the
fungus material as their food. They do not eat the leaves. It is the fungus
they grow from which they feed. Pathogenic fungus Escovopsis sp. can overcome
the useful Leucoagaricus sp. fungus and the colony starves.
The authors found that ant-associated microorganisms such as Pseudonocardia,
Dermacoccus, and Streptomyces control the invasive fungus Escovopsis. The
strain Streptomyces sp. produces the antibiotic candicidin which is effective
against Escovopsis but does not interfere in the growth of the ant food fungus.
[2177]
Leaf-cutting ants maintain an obligate symbiosis with their fungal garden. The
ants and their cultivar have to cope with hundreds of endophytic fungal species
which are brought in with the leave cuts.
Endophytes are a bacterium or fungus, that live
within a plant for at least part of its life without causing apparent disease.
Endophytes may benefit host plants by preventing pathogenic organisms from
colonizing them. Fungal endophytes may outcompete the fungal cultivar of the nest.
Van Baels and colleagues 2009 found that ants control endophytes applying
strategies like preferring to cut leaves from low endophyte densities, they
reduce the amount of endophytic fungi in leaves before storing them in their nest
and the original fungal cultivar inhibits the growth of foreign fungi that might
out-grow the cultivar.
[2178]
Entomologists Ted Schultz and Seán Brady explain that agriculture is a
specialized form of symbiosis which evolved in only four animal groups:
humans, bark beetles, termites, and ants. Evolution produced the five
distinct agricultural systems of the fungus-growing ants, resulting from a
single ancestor living 50 million years ago.
In the past 25 million years, four different specialized agricultural systems
have evolved, leading to the most recently evolved and best-known fungus-growing
ant species-leaf-cutter ants. Leaf-cutter ants originated recently-less than 10
million years ago.
[2179]
The fungal garden which serves as food for the ant colony is grown from a few
strands of the garden of origin. The queen carries them in her mouth on her
mating flight to start a new colony.
Mikheyev, Mueller and Abbot 2006 describe evidence of recombination in
attine fungal cultivars, contradicting widely held perceptions of obligate clonality.
Mikheyev and Mueller 2006 studied the coevolutionary process of the
dependence of fungus-farming ants on fungus gardens for food. The researchers
found that the ants were dependent on the fungus, but no dependence of the
fungus on the ant was stringent. The fungus-growing ants were seen as a
coevolutionary integration.
The fungi occasionally reproduce sexually by spores carried by wind. It exchanges
genes with other ant-cultivated fungi. According to genetic analysis made by the
authors the fungus of Cuba exchanged genes with mainland fungi populations of
Central and South America brought in by winds. The fungus is still using its
sexual reproduction and is not completely dependent on asexual, clonal
reproduction through their ant farmers. This is an example that coevolution does
not imply mutual dependence.
Biological coevolution is the change of a biological
object triggered by the change of a related object. Coevolution can occur at
multiple levels of biology: it can be as microscopic as correlated mutations
between amino acids in a protein, or as macroscopic as covarying traits
between different species in an environment. Each party in a coevolutionary
relationship exerts selective pressures on the other, thereby affecting each
others' evolution. Species-level coevolution includes the evolution of a host
species and its parasites, and examples of mutualism evolving through time
A species may evolve in response to a number of other species, each of which is
also evolving in response to a set of species. This situation has been referred
to as "diffuse coevolution". And, certainly, for many organisms, the biotic
(living) environment is the most prominent selective pressure, resulting in
evolutionary change. [2180]
[2181]
Carrero and colleagues 1997 isolated 137 yeasts associated with the leaf-cutting
ant Atta sexdens rubropilosa Forel, 1908. Candida, Cryptococcus, Rhodotorula,
Sporobolomyces, Tremella, Trichosporon, Pichia and black yeasts were isolated by
the authors. The genus Candida was widely distributed, with C. homilentoma, C.
colliculosa-like, C. famata and C. colliculosa being the most prevalent.
[2182]
Crush the
head of a soldier ant between your fingers. A lemon-like odor characterises this
ant.
Same identification as foregoing.
The largest workers of the colony have a smooth and
shining head, similar to glass.
Its colour is brown-yellow not shining.
It prefers
grass instead of leaves. It differs from the foregoing ants in not producing a
lemon smell, it is not brilliant,Its head is not brown yellow
It is recommended to find vertical holes which lead directly to the centre of
the colony to apply the liquid poison, powder or fumes. Baits should be left
on the trail of the ants. Application of poison must follow the instructions
of the producer.
Chemical used in form of gases and powder are applied directly to the nest. Baits
are carried to the fungal garden by worker ants but are not accepted by all sort
of ants. The strategy varies according to the ant which is to be controlled. It
is difficult to eradicate leaf cutter ants with dust, liquid or granular
insecticides because the centre of the nests, with the fungal garden is often
missed. Bits are often not accepted. Baits with hydramethylnon are in use to
control leaf cutting ants. [2183]
[2184]
Wuellner and colleagues 2002 suggest biocontrol of leave-cutting ants using
phorid flies such as Pseudacteon tricuspis and Pseudacteon obtusus for the
control of the red imported fire ant in geographical areas where polygyne
colonies dominate, such as Texas. For Florida, where monogyne colonies dominate,
Pseudacteon litoralis is being recommended by the authors.
Gyne is the primary reproductive female caste of social
insects (especially ants, wasps, and bees of order Hymenoptera). Gynes are
those destined to become queens, whereas female workers are typically sterile
and cannot become queens. A colony with multiple queens is said to be a
polygyne form, where as with only one is a monogyne form. The fire ant
Solenopsis invicta is known to have colonies in both polygyne and monogyne
forms. [2185]
Female phorid flies Pseudacteon obtusus were released in Texas in 2008-2009.
The flies inject their eggs into the ants. The resulting larvae migrate to
the ant's head where it feeds from the ant's brain and decapitates its host to
hatch. [2186] [2187]
The combination of biocontrol using phorid flies in combination with chemical
poisoning of ant colonies is being suggested. The chemical control is very
effective, but does not avoid a new infestation from colonies which had been
overseen.
[2188]
Insect hormones. More than 90% of insect hormones are neuropeptides.
Researchers try to understand the function of insect neuropeptides, which
are hormones which have important functions during insect developmental and
as adults. With increase knowledge on this matter dependence on poisonous
chemicals may be reduced.
Choi, Raina and Vander Meer 2009, studying the fire ant, Solenopsis invicta,
found the pyrokinin/pheromone-biosynthesis-activating neuropeptide (PBAN),
which is a family of peptides. This pentapeptide stimulates the production
of pheromone in female moths, muscle contraction, induction of embryonic
diapause, melanization, acceleration of puparium formation, and termination of
pupal diapause.
The authors hope to increase knowledge about the regulation of pheromone
production their release, and how neuropeptides they influence the development
of ants. Researches in this field may create non-insecticide methods for fire ant
control by interfering in the normal neuropeptide hormone function.

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