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FACTORS AFFECTING HERBICIDE EFFICACY
Lynn M. Sosnoskie, PhD
Department of Plant Sciences
University of California, Davis
Photo from: A.S. Culpepper
Herbicides are, for many, a critical component of weed control programs
(21 selected crops 1960-2008)
Herbicides may not be 100% effective…
Photo from: A.S. Culpepper
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Almond image: Mullookkaaran, Sugar beet image: Jacopo Werther. Grapes: Ian L. Use does not signify endorsement.
ACCase ALS inhibitors
glyphosate
ACCase ALS inhibitors
ACCase glyphosate
Herbicide Resistance in Washington Year Species Site of Action Actives 1970 Common Groundsel Photosystem II inhibitors simazine
1987 Russian-thistle ALS inhibitors chlorsulfuron
1988 Yellow Starthistle Synthetic Auxins picloram
1989 Kochia ALS inhibitors chlorsulfuron
1991 Wild Oat ACCase inhibitors diclofop-methyl
1992 Powell Amaranth Photosystem II inhibitors terbacil
1993 Prickly Lettuce ALS inhibitors chlorsulfuron
2000 Spiny Sowthistle ALS inhibitors imazamox, others
2007 Prickly Lettuce Synthetic Auxins 2,4-D, dicamba, MCPA
2010 Redroot Pigweed Photosystem II inhibitors metribuzin, terbacil
2010 Common Lambsquarters Photosystem II inhibitors metribuzin, terbacil
2010 Mayweed Chamomile ALS inhibitors cloransulam-methyl, others
Trade Name Chemical WSSA Code Resistance PNW? Fusilade fluazifop 1 Yes Poast sethoxydim 1 Yes Select (and others) clethodim 1 Yes Matrix (and others) rimsulfuron 2 Yes Kerb pronamide 3 Yes Prowl H2O (and others) pendimethalin 3 Yes Surflan (and others) oryzalin 3 Yes Treflan (and others) trifluralin 3 Yes Princep (and others) simazine 5 Yes Karmex (and others) diuron 7 Yes Roundup (and others) glyphosate 9 No Rely (and others) glufosinate 10 Yes Solicam norflurazon 12 No Aim carfentrazone 14 No Chateau flumioxazin 14 No Goal (and others) oxyfluorfen 14 No Venue pyraflufen 14 No Devrinol napropamide 15 Yes
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How do we get from this…
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Herbicide resistance is an evolutionary process
Herbicide applications don’t change the weeds genes to make them resistant The gene changes that confer resistance are already present in the species Repeated use of a herbicide removes susceptible biotypes…leaving resistant plants that then reproduce After time, resistant offspring from the resistant source begin to dominate the population
Evolution of herbicide resistance
A A A 2.0 A B B
Time
Poor Weed Control Is More Than Just Resistance
Boom height
Weed height
Factors affecting herbicide efficacy
Weed
Herbicide Environment
Herbicide MOA, Application, Rate, Spray Solution
Image: Tamina Miller. Use does not signify endorsement.
MOA affects Selectivity (Choosing the right herbicide for the weed)
AUXINIC HERBICIDES
Selective for broadleaf spp.
Phenoxycarboxylic acids
Picolinic acids
Pyrachlor
Benzoic acid
Quinoline carboxylic acid
ACC-ASE INHIBITORS
Selective for grass spp.
Cyclohexadienes (-dims)
Aryloxyphenoxypropionates (-fops)
Differences in Efficacy (CSU Extension Turf Weed Management CMG Garden Notes #552)
Herbicide class a.i. Dandelion Bindweed Crabgrasses Foxtails
Phenoxycarboxylic acid 2,4-D Good
Picolinic acid triclopyr Good Good
Quinoline carboxylic acid quinclorac Good Good Good
Method of Application (How the herbicide is applied in the environment to control weeds)
Pre-emergence Post-emergence
Credit: A.S. Culpepper
Differences in Weed Control Spectrum PRE vs. POST (CA Tomatoes)
RIMSULFURON (MATRIX SG) PRE
Barnyardgrass
Giant, green, yellow foxtail
Henbit
Kochia
Redroot and smooth pigweed
Common purslane
RIMSULFURON (MATRIX SG) POST Barnyardgrass Annual bluegrass Barley, giant, green, yellow foxtail Fall panicum Henbit Kochia Redroot and smooth pigweed Common purslane Shepherd’s purse Wild radish Chickweed Mustard spp.
Source: Matrix SG label, Dupont
Differences in Weed Control Spectrum PRE vs. POST (CA Tomatoes)
RIMSULFURON (MATRIX SG) PRE RIMSULFURON (MATRIX SG) POST
Source: Matrix SG label, Dupont
Bindweed: YES Bindweed: NO (Vine suppression)
Herbicide Rate (Control of grass spp. in citrus with Roundup Powermax)
Weed 0.7 QT/A 1.3 QT/A 2 QT/A 3.3 QT/A
Bermudagrass Burndown - Partial control Control
Paragrass Burndown Control Control Control
Torpedograss Suppression - Partial control Control
Source: Roundup Powermax label, Monsanto
Spray Solution Water quality (Spray solutions are >95% water)
What goes in can affect what comes out
Glyphosate is one of the best examples
pH – high pH causes glyphosate to dissociate
Cations – Mg, Ca, Na can bind to glyphosate
Turbidity – glyphosate tightly bound to soil and OM
Tank Mixing (via Andrew Kniss U. Wyo.)
Mixtures of two herbicides are far more effective at slowing the evolution of herbicide resistant weeds compared to an annual rotation of herbicides (You still need to rotate, tho!) BUT… BOTH HERBICIDES must be effective on the target weed If one of the herbicides is not effective, then there is still heavy selection pressure for weeds resistant to the other herbicide AND… The tank-mixture strategy also only works with the most common resistance mechanisms; other types of herbicide resistance (like metabolic resistance) are potentially more likely to occur when multiple herbicides are used
2010 1980 1940
1950-1954 diuron
1955-1959 simazine
1960-1964 dichlobenil trifluralin
Timeline of Herbicide Introductions for PRE Products Registered in WA Vine Crops*
* Timeline is based on 2015 registrations in CA; not all herbicides are registered in all crops. Years represent data reported in Timmons (1970) Weed Sci. 18:294-307, Appleby (2005) Weed Sci. 53:762-768, and the EPA. Dates are of the first
recorded registration/use in any crop, not necessarily tree nuts, fruit trees, and/or vines.
1970-1974 napropamide norflurazon oryzalin pendimethalin pronamide
1975-1979 oxyfluorfen
1980-1984 isoxaben
1985-1989 flazasulfuron
1990-1994 flumioxazin sulfentrazone
2010-present indaziflam
2010 1980 1940
Timeline of Herbicide Introductions for POST Products Registered in WA Vine Crops*
* Timeline is based on 2015 registrations in CA; not all herbicides are registered in all crops. Years represent data reported in Timmons (1970) Weed Sci. 18:294-307, Appleby (2005) Weed Sci. 53:762-768, and the EPA. Dates are of the first
recorded registration/use in any crop, not necessarily tree nuts, fruit trees, and/or vines.
1970-1974 glyphosate
1980-1984 fluazifop glufosinate sethoxydim
1965-1969 paraquat
1990-1994 carfentrazone pyraflufen
1985-1989 rimsulfuron
Duk
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012)
. Pes
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Cumulative a.i. Introductions versus Issued Herbicide Patents per Year
Weed Biology/Ecology Identity, Life Cycle, Morphology, Size
Herbicides and Nutsedge Control
Metolachlor = <20% Glyphosate = 70%
Metolachlor = 55-75% Glyphosate = 55%
Life Cycle (Annual vs Perennial)
An extensive root system makes field bindweed very tolerant of control measures
Root system of field bindweed, Convolvulus arvensis. Redrawn from B. F. Kiltz. 1930 J. Amer. Soc. Agron. 22:216-234
Plant morphology can affect herbicide capture and absorption
Leaf orientation Location of meristems Leaf area Hairiness
When it comes to weed control, size and timing matters M
eme
cour
tesy
of B
ill P
rice
Plant Density and Spray Interference Greater numbers of weeds will require greater weed
control efforts to prevent escapes
Credit: T.M. Webster
Probability of finding a mutation that confers resistance increases as plant density increase
Jasieniuk et al. (1996)
Est. Mutation Rate Weeds/m2 Probability of occurrence of at least one mutant plant in 30 ha fields
1 x 10-6 1 0.45 5 0.95
50 1.00 500 1.00
1 x 10-8 1 0.006 5 0.03
50 0.26 500 0.95
Est. “typical” spontaneous genetic
mutation rate (gametes/locus/gen.)
Est. spontaneous genetic mutation rate
for ALS-R (gametes/locus/gen.)
Results are estimates for a single dominant nuclear gene mutation in a random-mating system.
Environment Soil, Water, Temperature, Wind
Soil ◦ Clay, OM can make herbicides
unavailable; affects rate required for control
◦ In less adsorptive soils, herbicide leaching can occur; too much herbicide can lead to crop injury
◦ Slope can lead to erosion or drainage; physical loss of treated soil
Water
◦ Soil moisture: ◦ Needed for activation of
residual herbicides
◦ Precipitation: ◦ Activation of herbicides ◦ Erosion, leaching ◦ Rain-fastness
Wind
◦ Spray drift (droplets)
◦ Dust drift (particles)
◦ Dust (barrier)
2,4-D damage on grapes. UC IPM
Temperature ◦ Herbicide effects ◦ Degradation
◦ Volatilization
◦ Plant stress ◦ Plant growth rate
◦ Cuticle development/herbicide absorption
◦ Herbicide translocation
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Time, in days, to reach 3” height following Palmer amaranth emergence
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4/11/2011 5/8/2011 5/10/2011 5/27/2011 6/15/2011
2 Weeks
1 Week
Herbicides Read the label, calibrate the sprayer, use adjuvants wisely Use multiple herbicide MOAs Apply herbicides at label rates and at recommended weed sizes Use mechanical, cultural, and biological practices when appropriate
Weeds Understand the biology of the weeds present Plant into weed free fields and keep fields as weed free as possible Prevent the movement of weed seed within and between fields Scout fields, borders routinely
Environment Apply sprays as are appropriate for soil, moisture, temperature, wind
BMPS FOR WEED RESISTANCE MANAGEMENT
Thank you for your time! I am a new scientist and I need you to help me to help you! I need you to tell me: • What YOUR biggest weed concerns
are.
• What management strategies (organic, conventional, mixed) YOU want investigated.
• What application tools (i.e. nozzles, spray rates) need more study.
• How the environment affects your weed control.
lynn.weed.science@gmail.com
@LynnSosnoskie on Twitter
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