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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.

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Presentation on theme: "S2 L5 Herbicides, biological control of pests, IPM Anna Drew With slide contribution from: Martin Wilks (Syngenta) Anuruddhika Abeysekara Peterson DE et."— Presentation transcript:

1 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

2 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

3 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

4 Common Rice Weeds in Wet land rice culture in Sri Lanka

5 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 –Persistence –Formulation –Site of action

6 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 chlorphenoxy: 2,4D, MCPA* benzoic acid: dicamba carboxylic acid: picloram, clopyralid, triclopyr, fluoxypyr quinolone: quinclorac

7 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 Bipyridilium: paraquat*, diquat organic arsenicals

8 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 –> white foliage –generally applied to soil, move through xylem (amitrol thru’ phloem) –eg isoxazolidinone: clomazone isoxazole: isoxaflutole pyridazinone: norflurazone

9 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

10 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

11 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

12 Paraquat characteristics l Quaternary ammonium salt l The positive charges on the molecule give rise to it’s unique properties l extremely soluble in water

13 l No systemic action so must ensure good coverage of target foliage to get good activity Paraquat – Mode of Action

14 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

15 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.

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

17 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 (LD 50 > 5000 mg/kg) –Non-ionic tallow amine surfactant (LD 50 1200 mg/kg)

18 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

19 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 -> 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

20 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

21 INSECTS –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 –Beauvaria bassiana – used to control termites, whitefly, beetles »= parasite -> white muscardine disease

22 –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: α- ecdysone, β-ecdysone Eggs JH ↓ MH Larva MH,JH ↓ MH Pupa MH ↓ MH Adult JH

23 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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