S2 L5 Herbicides, biological control of pests, IPM

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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

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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

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• Types of weeds
• Annual
• Biannual
• Perennial
• long roots
• harder to kill
• Seedling
• most susceptible stage of weed
• Currently
• Weed flora shifting - Annual -gt
  Perennial
• due to continuous application of herbicides
• and poor management practices

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Common Rice Weeds in Wet landrice culture in Sri
Lanka
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• Classification
• Selectivity
• 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

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By site of action

• Plant growth regulators
• Action mimics natural plant growth hormones
  auxins
• (regulate cell elongation, protein synthesis,
  cell division)
• -gt imbalance of growth regulating hormone
• disrupts vascular tissue - leaf veins divide
  faster than cells in between
• Use controlling broadleaf weeds in grass crops
• Eg
• chlorphenoxy 2,4D, MCPA
• benzoic acid dicamba
• carboxylic acid picloram, clopyralid, triclopyr,
  fluoxypyr
• quinolone quinclorac

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• 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
• diphenylether acifluorfen
• Aryl triazolinone sulfentrazone
• Phenylphthalimide flumiclorac

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• Photosynthesis inhibitors
• 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 gt white foliage
• generally applied to soil, move through xylem
  (amitrol thru phloem)
• eg
• isoxazolidinone clomazone
• isoxazole isoxaflutole
• pyridazinone norflurazone

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• Amino acid synthesis inhibitors
• necessary for plant protein production
• activity associated with a specific AA sequence
• slow acting
• eg
• 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

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Eg - Tested in Sri Lanka - NCHST

• Tested crop Wet seeded rice
• Included program NCHST
• Season 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

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Short history of paraquat

• Herbicidal properties discovered by ICI in 1955
• 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
  its unique properties
• extremely soluble in water

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Paraquat Mode of Action

• No systemic action so must ensure good
• coverage of target foliage to get good
  activity

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Benefits of paraquat use

• Broad-spectrum weed control
• Flexible use
• 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

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Paraquat Safety in Use

• Almost all (gt99) occupational exposure is
  dermal.
• Paraquat is poorly absorbed through human skin (lt
  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.

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• Chlorphenoxy-
• 2,4-D (2,4-dichlorophenoxyacetic acid)
• MCPA (4-chloro-2-methylphenoxyacetic acid)
• Propanil
• 3,4-dichloropropioanilide (acylanilide)
• popular for rice paddy

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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 gt 5000
  mg/kg)
• Non-ionic tallow amine surfactant (LD50 1200
  mg/kg)

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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

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Biological pest control

• FUNGI
• Plant breeding to produce resistance to pests
• in order to maintain crop quality
• survival of the fittest in wild plants
• cross with non-wild plant -gt 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

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• 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

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• INSECTS http//en.wikipedia.org/wiki/Biological_c
  ontrol
• 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
• 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

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• 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 a-ecdysone,
  ß-ecdysone

Eggs JH
? MH
Larva MH,JH
? MH
Pupa MH
? MH
Adult JH
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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

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