S2 L5 Herbicides, biological control of pests, IPM

Anna Drew

With slide contribution from:Martin Wilks (Syngenta)Anuruddhika AbeysekaraPeterson 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 landrice 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• 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

• 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

• diphenylether: acifluorfen• Aryl triazolinone: sulfentrazone• Phenylphthalimide: flumiclorac• Bipyridilium: paraquat*, diquat• organic arsenicals

• 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

• 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

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

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

Paraquat characteristics

Quaternary ammonium salt

The positive charges on the molecule give rise to it’s unique properties

extremely soluble in water

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

Paraquat – Mode of Action

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

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 (2,4-dichlorophenoxyacetic acid)

– MCPA (4-chloro-2-methylphenoxyacetic 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• 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– 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: α-

ecdysone, 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]