Transcript S2 L5 Herbicides, biological control of pests, IPM

S2 L5 Herbicides, biological
control of pests, IPM
Anna Drew
With slide contribution from:
Martin Wilks (Syngenta)
Anuruddhika Abeysekara
Peterson DE et al (Kansas State University)
Prostko EP (University of Georgia)
Rondha Hamm
Herbicides
• Chemicals that inhibit or
interrupt normal plant
growth and development
• Used for:
– food crops
• rice in Sri Lanka
– draining/ reclaiming land
– killing aerial parts of plants
• to make harvest easier
• eg potato
• Types of weeds:
– Annual
– Biannual
– Perennial
• long roots
• harder to kill
– Seedling
• most susceptible stage of weed
• Currently:
Weed flora shifting -
Annual -> Perennial
due to continuous application of herbicides
and poor management practices
Common Rice Weeds in Wet land
rice culture in Sri Lanka
Grasses
Sedges
Broadleaves
Echinochloa colonum
Cyperus iria
Mononochoria vaginalis
Echinochloa crussgalli
Cyperus difformis
Commelina diffusa
Panicum repens
Cyperus rotundus
Eclipta alba
Ischeamum rugosum
Fimbristyllis miliacea
Eichornia crassipes
Isachne globosa
Fimbristylis dichotama
Limnocharis flava
Leptochloa chinensis
Fuirena cillaris
Linderina spp.
Paspalum distichum
Scirpus supinus
Ludwigia perenesis
• Classification:
– Selectivity
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ability to kill certain plants and not others
non-selective, grass, broad leaf control etc
paraquat, glyphosate = non-selective
[crops can be genetically engineered to resist glyphosate]
relative depending on
– environment, application rate, application timing, application technique
– Time of application
• pre-plant incorporated, pre-emergence, post-emergence
– Method of application
• Foliar applied, soil applied, broadcast, spot
– Translocation in the plant
• Contact (none), systemic
– Persistence
– Formulation
– Site of action
By site of action
• Plant growth regulators
– Action: mimics natural plant growth hormones –
auxins
• (regulate cell elongation, protein synthesis, cell division)
• -> imbalance of growth regulating hormone
• disrupts vascular tissue - leaf veins divide faster than cells in
between
– Use: controlling broadleaf weeds in grass crops
– Eg
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chlorphenoxy: 2,4D, MCPA*
benzoic acid: dicamba
carboxylic acid: picloram, clopyralid, triclopyr, fluoxypyr
quinolone: quinclorac
• Seedling growth inhibitors
– seedling shoot inhibitors
• eg carbamothioates: EPTC, butylate, triallate
– seedling root and shoot inhibitors
• eg acetamides: alachlor, dimethenamid, flufenacet
– microtubule assembly inhibitors
• mitotic poisons that inhibit cell division (meristem)
• eg dinitroanilines: trifluralin, benefin
• Cell membrane disrupters
– destroy cell membranes allowing contents to leak out
– Eg
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diphenylether: acifluorfen
Aryl triazolinone: sulfentrazone
Phenylphthalimide: flumiclorac
Bipyridilium: paraquat*, diquat
organic arsenicals
• Photosynthesis inhibitors
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photosynthesis is shut down
generally applied to soil, move through xylem
foliage and stems affected not roots
plants turn yellow and die due to chlorophyll
breakdown
– eg pyridate, bromoxynil, atrazine, bromacyl, diurenon,
hexazinone, simazine, tebuthiuron
• Pigment inhibitors
– cause chlorophyll destruction –> white foliage
– generally applied to soil, move through xylem (amitrol
thru’ phloem)
– eg
• isoxazolidinone: clomazone
• isoxazole: isoxaflutole
• pyridazinone: norflurazone
• Amino acid synthesis inhibitors
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necessary for plant protein production
activity associated with a specific AA sequence
slow acting
eg
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imidazolinones: imazithapyr
sulphonylureas: bensulfuron-methyl
triazolopyrimidine: flumetsulam, cloransulam
amino acid derivative: glyphosate*, glufosinate
• Lipid biosynthesis inhibitors
– meristematic cell membrane integrity affected
– eg
• aryloxyphenoxypropionate: diclofop, fluazifop
• cyclohexandione: sethoxydim
Eg - Tested in Sri Lanka
Tested crop :
Included program:
Season:
- NCHST
Wet seeded rice
NCHST
Maha 99/2000 & yala 2000
Formulation tested:
10% WP
Rate of Application:
250g/ha
Time of application:
post emergence (15-25 DAS)
Application method :
Foliar application
Field condition:
Drained at application time
Water management:
Flooded 1 to 3 days after application
Target weeds:
common sedges and broad leaf weeds in rice
Short history of paraquat
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Herbicidal properties discovered by ICI in 1955
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First little enthusiasm - was not selective and deactivated in soil
First uses oil palm and pasture renovation 1962,
A pioneering herbicide – replaced handweeding, enabled
development of minimum tillage
Researchers and farmers discovered amazing versatility of
compound
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Paraquat characteristics

Quaternary ammonium salt

The positive
charges on the
molecule give
rise to it’s
unique
properties
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extremely
soluble in
water
Paraquat – Mode of Action
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No systemic action so must ensure good
coverage of target foliage to get good activity
Benefits of paraquat use
• Broad-spectrum weed control
• Flexible use :
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Tillage systems, Tankmix
Rainfast – 30 minutes
Burndown in as little as 48 hours
Performs well in cooler, wet
conditions
• Improves yields and
productivity
• Reduces cultivation,
encourages no-till
Paraquat Safety in Use
• Almost all (>99%) occupational exposure is dermal.
• Paraquat is poorly absorbed through human skin (< 0.3%).
• Inhalational exposure is negligible
– Practically non-volatile
– Droplet size too large to be inhaled
• Numerous health studies and surveys have confirmed that
paraquat is safe in normal occupational use.
• Chlorphenoxy– 2,4-D (2,4dichlorophenoxyacetic
acid)
– MCPA (4-chloro-2methylphenoxyacetic acid)
• Propanil
• 3,4-dichloropropioanilide
(acylanilide)
– popular for rice paddy
Glyphosate
• Chemically related to
organophosphates but does not
cause cholinesterase inhibition
• Acts systemically after absorption
by inhibiting a plant-specific
enzyme needed for protein
biosynthesis
• Toxicity dependent on formulation
– Isopropylamine salt of glyphosate
(LD50 > 5000 mg/kg)
– Non-ionic tallow amine surfactant
(LD50 1200 mg/kg)
Natural weedkillers (garden)
• eugenol (clove oil)
• acetic acid (vinegar)
• fair to good control of small seeded broadleaves
• citric acid
• rock salt
• not good
• boiling water
• sugar
• dried molasses
• corn gluten meal
• barriers
Biological pest control
• FUNGI
– Plant breeding to produce resistance to pests
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in order to maintain crop quality
‘survival of the fittest’ in wild plants
cross with non-wild plant -> best genes
many years to develop
pest may mutate quickly
eg cereals
woody plant root stocks susceptible to fungi so harder to do (wild
root may be grafted to cultivated aerial plant parts)
– Factors altered or developed for:
• Hairs on leaves
– alters moisture levels around the leaf
– changes humidity to stop fungal spores taking control
• Waxy cuticle
– Prevents spores taking hold
• Penetration point
– Stomata and trichomes
– Some plants developed so that necrosis occurs where the fungus
penetrates and cuts of food supply for fungus
• Toxins
– Some plants naturally produce toxins to pests
– Look at plants natural chemical resistance
– Preinfected compounds (proinhibins):
» Eg onion – procatechinic acid, catechinic acid
– Inhibins:
» Compounds already in plant which increase with infection
» Eg luteone from Lupinus sp.
– Proinfectinal compounds
» Developed when infection has already occurred
» Eg phytoalexins – pisatin
– Can artificially stimulate phytoalexin levels with heavy metals +/ultraviolet light
– Can alter sugar levels in plants depending on what fungus requires
– Can alter phenol and amino acid levels by spraying
– Can induce stomata closure when atmospheric conditions are best for
fungal infection
• INSECTS
http://en.wikipedia.org/wiki/Biological_control
– A. Use of natural predators
• Success with a scale insect imported from Australia to citrus
fields of California
– also imported predator Rodelia cardinalis
– needed a contained population
• Trichogramma sp attack eggs of all insects
– eg used to control cotton boll worm
• Bacteria
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Eg gypsy/codling moth
Caterpillar stage eats leaves of N.American deciduous forests
Tried aerial spraying but people live there
Bacillus thuringiensis (Bt) dissolves away gut of moth
• Fungi
– Entomopathogenic – 14 species that attack aphids
– Beauvaria bassiana – used to control termites, whitefly, beetles
» = parasite -> white muscardine disease
– B. Sterilisation of insects
• UV radiation
– female may no longer be attracted to male
» if more differences are produced
» need a contained population
• Chemicals
– male - aziridines: TEPA, thiotepa
– female - 5-fluorouracil
» very cytotoxic – caution in handling
» bating trays with ‘sex lures’ to attract
one sex
» used inside fly traps so can check if
part of population affected
• Insect cycle can also be controlled by
» Juvenile hormones – simple terpenes:
juvabione
» Moulting hormones – steroidal: αecdysone, β-ecdysone
Eggs
↓
JH
MH
Larva MH,JH
↓
MH
Pupa
MH
↓
MH
Adult
JH
Integrated pest management
• Pest control strategy based on the determination of an
economic threshold that indicates when a pest
population is approaching the level at which control
measures are necessary to prevent a decline in net
returns. Considers economic, ecological and sociological
goals. [Pfadt, 1985]
• In principle IPM is “an ecologically based strategy that
relies on natural mortality, such as natural enemies,
weather and crop management, and seeks control
tactics that disrupt these factors as little as possible.”
[Flint and van den Bosch, 1981]