WEED MANAGEMENT INCALIFORNIA RICE

History of Weeds in CA RiceCommercial rice production introduced in CA in 1912 when 1,400 Ac were grown by dry-seeded culture.

1924 – Dr. Jenkins Jones wrote that “practically all, if not all of the lands – and these represent the major portion of the rice acreage – are quite foul with watergrass”, and that on these lands it was “practically impossible to grow profitable rice crops”.Dr. Jones’ research led to water-seeded rice and a new set of weed problems.

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Evolution of Weed Issues in CA RiceWater-seeding led to a new set of weed problems.

Large seeded watergrass biotypes that would emerge through continuous flood and a new set of aquatic weeds

Sedge species, aquatic broadleaf species, and late watergrass biotypes (“mimic”)

Since 1992, several weed species have evolved resistance to herbicides

Multiple resistancesAdvent of foliar applied herbicides has increased complexity of water management and hence weed control

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Increased Complexity of Weed ControlKnowledge Intensive Management

Knowledge of the weed species presentKnowledge of weed species resistance and to what herbicideKnowledge of herbicide behaviorKnowledge of mixtures and sequentialsGood water management capabilityKnowledge of application requirements

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Cultural Methods of Weed Control

PreventionTillageWater ManagementRotation

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Prevention

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Certified Seed0 Red Rice0.01% Echinochloa spp

barnyardgrasswatergrass

Clean Equipment

Clean Water

Tillage

LevelingHigh spots - weed germinationLow spots – inadequate foliar herbicide coverage

TillageDry seedbed

Overwintering rhizomes or corms of perennialsPrevent weed head start

Straw incorporationIncorporates weed seed and prevents depredation

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Water Management

Most important factor in managing rice weedsIdeally, continuous flood 4-8” deep

Suppresses grasses and smallflower umbrella sedge

Foliar active and contact herbicidesRequire drainage for good coverageRapid reflooding to prevent new flushNeed ability to drain and flood quickly

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Rotation

Other cropsLimited areas

Pre-plant weed controlStale seedbed Minimum till

Dry seedingDrillBroadcast

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The common and trade names of current herbicides for rice in CA

bensulfuron Londax®

bispyribac Regiment®

carfentrazone Shark®

clomazone Cerano®

cyhalofop Clincher®

halosulfuron Sempra®

fenoxaprop Whip®

pendimethalin Prowl®penoxulam Granite®

propanil Stam®, SuperWham®

thiobencarb Abolish®, Bolero®

triclopyr Grandstand®

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The Herbicides

Need to understand the specific attributes of a given herbicide to achieve efficient weed control

Application timing, field management and environmental conditions may all increase or decrease controlCarefully read and follow label for rate, adjuvants, combinations and other conditionsMixing and matching the herbicides a complete spectrum of weed control may be possible

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Herbicide Combinations

Tank mixes can be used when two or more herbicides are compatible

Chemically compatibleAvoid antagonism that may result in loss of control of injury to rice

Application conditions compatibleMay reduce application costs and possibly ratesPurpose is to broaden spectrum of weed control

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Herbicide Sequences

Used to achieve broad-spectrum weed controlInstead of tank mix due to differences in timing, water management, antagonism, translocation and other factorsUse different modes of action to protect against resistance management

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Herbicide Behavior

ActivityTranslocationApplication windowsResidual activityResistance and mechanism of action

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Table 5. Behavior of currently used herbicides(lsr - rice leaf stage; mt = mid-tillering).

Herbicide Foliar Appl’din

Water

Translocation Index

Timing Window

Residual (days)

WeedResistance

Abolish Yes Yes 3 1-2 lsr 20-25 YesBolero No Yes 3 1-2 lsr 20-25 YesCerano No Yes 6 0-1 lsr 5 in water Ltd. in lwg.ClincherGranite

YesYes

NoYes

44

2 lsr – mt2 lsr

035-40

YesYes

Regiment Yes No 4 5 lsr – mt 0 YesSuperWham Yes No 3 3 lsr – mt 0 NoStam Yes No 3 3 lsr – mt 0 NoWhip Yes No 4 5 lsr – mt 0 YesLondax Yes Yes 4 0-5 lsr 35-40 YesGrandstand Yes No 8 5 lsr – mt 0 NoSharkProwl

YesNo

YesNo

20

4 lsr – mtsoil

cracking

5-820 dry soil

5 water

NoNo

Foliar Versus Soil Activity

Many newer herbicides are only active as foliar spraysGenerally, granular herbicides are active through the soil and taken up by the rootSome herbicides have soil and foliar activity

Abolish, Londax, SharkNeed to understand for water management

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Table 5. Behavior of currently used herbicides(lsr - rice leaf stage; mt = mid-tillering).

Herbicide Foliar Appl’din

Water

Translocation Index

Timing Window

Residual (days)

WeedResistance

Abolish Yes Yes 3 1-2 lsr 20-25 YesBolero No Yes 3 1-2 lsr 20-25 YesCerano No Yes 6 0-1 lsr 5 in water Ltd. in lwg.ClincherGranite

YesYes

NoYes

44

2 lsr – mt2 lsr

035-40

YesYes

Regiment Yes No 4 5 lsr – mt 0 YesSuperWham Yes No 3 3 lsr – mt 0 NoStam Yes No 3 3 lsr – mt 0 NoWhip Yes No 4 5 lsr – mt 0 YesLondax Yes Yes 4 0-5 lsr 35-40 YesGrandstand Yes No 8 5 lsr – mt 0 NoSharkProwl

YesNo

YesNo

20

4 lsr – mtsoil

cracking

5-820 dry soil

5 water

NoNo

Contact or Translocated

Does the herbicide move in the plant?Contact herbicides move very little from point of impact and kill only that part of the plant that is contacted by the spray (Shark, SuperWham, Stam)Translocated herbicides move from the site of uptake to other parts of the plant to kill the growing point (Grandstand)Some herbicides move small distances (Whip, Clincher, Regiment)Cerano moves but only upward

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Table 5. Behavior of currently used herbicides(lsr - rice leaf stage; mt = mid-tillering).

Herbicide Foliar Appl’din

Water

Translocation Index

Timing Window

Residual (days)

WeedResistance

Abolish Yes Yes 3 1-2 lsr 20-25 YesBolero No Yes 3 1-2 lsr 20-25 YesCerano No Yes 6 0-1 lsr 5 in water Ltd. in lwg.ClincherGranite

YesYes

NoYes

44

2 lsr – mt2 lsr

035-40

YesYes

Regiment Yes No 4 5 lsr – mt 0 YesSuperWham Yes No 3 3 lsr – mt 0 NoStam Yes No 3 3 lsr – mt 0 NoWhip Yes No 4 5 lsr – mt 0 YesLondax Yes Yes 4 0-5 lsr 35-40 YesGrandstand Yes No 8 5 lsr – mt 0 NoSharkProwl

YesNo

YesNo

20

4 lsr – mtsoil

cracking

5-820 dry soil

5 water

NoNo

Window of Application

Herbicides vary widely in their ability to kill weeds of different sizes and their safety to rice at different growth stagesLabel timing is meant to lessen damage to rice and maximize weed control

Cerano, Bolero, Abolish very narrow windowsMany newer herbicides have broader windows

Important when weed control is delayed or as clean-up

Important to remove weeds before competition affects yield

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Table 5. Behavior of currently used herbicides(lsr - rice leaf stage; mt = mid-tillering).

Herbicide Foliar Appl’din

Water

Translocation Index

Timing Window

Residual (days)

WeedResistance

Abolish Yes Yes 3 1-2 lsr 20-25 YesBolero No Yes 3 1-2 lsr 20-25 YesCerano No Yes 6 0-1 lsr 5 in water Ltd. in lwg.ClincherGranite

YesYes

NoYes

44

2 lsr – mt2 lsr

035-40

YesYes

Regiment Yes No 4 5 lsr – mt 0 YesSuperWham Yes No 3 3 lsr – mt 0 NoStam Yes No 3 3 lsr – mt 0 NoWhip Yes No 4 5 lsr – mt 0 YesLondax Yes Yes 4 0-5 lsr 35-40 YesGrandstand Yes No 8 5 lsr – mt 0 NoSharkProwl

YesNo

YesNo

20

4 lsr – mtsoil

cracking

5-820 dry soil

5 water

NoNo

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Residual Activity

Important attribute in preventing reinfestation by new flushes of weed germination

Generally determined by strength of soil adsorption and rate of herbicide degradationMuch more important for early applications before rice canopy is capable of shading out weeds

Mixing a residual herbicide with an early application of a foliar herbicide such as propanil can sustain control long enough for rice canopy to closeBe cognizant of resistance selection with residual herbicides

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Table 5. Behavior of currently used herbicides(lsr - rice leaf stage; mt = mid-tillering).

Herbicide Foliar Appl’din

Water

Translocation Index

Timing Window

Residual (days)

WeedResistance

Abolish Yes Yes 3 1-2 lsr 20-25 YesBolero No Yes 3 1-2 lsr 20-25 YesCerano No Yes 6 0-1 lsr 5 in water Ltd. in lwg.ClincherGranite

YesYes

NoYes

44

2 lsr – mt2 lsr

035-40

YesYes

Regiment Yes No 4 5 lsr – mt 0 YesSuperWham Yes No 3 3 lsr – mt 0 NoStam Yes No 3 3 lsr – mt 0 NoWhip Yes No 4 5 lsr – mt 0 YesLondax Yes Yes 4 0-5 lsr 35-40 YesGrandstand Yes No 8 5 lsr – mt 0 NoSharkProwl

YesNo

YesNo

20

4 lsr – mtsoil

cracking

5-820 dry soil

5 water

NoNo

Mechanism of Action

Group Active Ingredient Mechanism of Action

Thiocarbamatesmolinate (Ordram)thiobencarb (Abolish, Bolero)

VLCFA (Very long chain fatty acids)

Aryloxyphenoxy-propionates

fenoxaprop (Whip)cyhalofop-butyl (Clincher) ACCase inhibitors

Amide propanil (SuperWham, Stam) Photosystem II inhibitor

SulfonylureaSulfonamide

bensulfuron (Londax)penoxsulam (Granite) ALS inhibitors

Phrimidinyl-oxybenzoates bispyribac (Regiment) ALS inhibitor

Dinitroaniline pendimethalin (Prowl) Tublin inhibitor (mitosis inh.)

Isoxazolidinone clomazone (Command) Carotenoid biosynthesis