Herbicide Resistance – Management and Prevention Brad Hanson
bhanson@ucdavis.edu brad.hanson@ars.usda.gov Weed School 2009
Outline • • • • • • •
Definitions Selection pressure Current state of affairs Factors contributing to resistance Preventing / delaying resistance Managing resistance Identifying resistance
Definitions • Herbicide tolerance: the inherent ability of a species to survive and reproduce after herbicide treatment; implies no selection or genetic manipulation to make the plant tolerant – “We’ve never gotten dependable control of this weed with this herbicide…”
• Herbicide resistance: the inherited ability of a plant to survive and reproduce following exposure to a dose of herbicide normally lethal to the wild type – “We used to be able to control this weed with this treatment but it doesn’t work as well anymore…”
Selection Pressure • Selection of HR is an evolutionary process – High genetic diversity in weed populations – Control measure remove susc. biotypes; leaves resistant plants to reproduce
• Pressure varies among systems – Cropping practices, herbicides, weeds
300
Chronological Increase in HRW
Number of Resistant Biotypes .
250 World USA
200
150
100
50
0 1950
1960
1970
1980 Year
1990
2000
Current State of Affairs • World wide – 113 dicots and 76 monocots – 19 herbicide families
• USA – 76 dicots and 52 monocots – 15 herbicide families
• California – 7 dicots and 14 monocots – 7 herbicide families Sept. 2009: www.weedscience.org
HRW in California
Year
20 08
20 06
20 04
Triazine (atrazine) Sulfonylurea Sulfonylurea Sulfonylurea Sulfonylurea Pyrazolium (difenzoquat) Sulfonylurea Sulfonylurea fops & thiocarbamates glyphosate Sulfonylurea fops & thiocarbamates fops & thiocarbamates fops and dims synthetic auxins glyphosate glyphosate glyphosate glyphosate & paraquat
20 02
20 00
19 98
19 96
19 94
Asparagus 1981 Roadside, railways 1989 Rice 1993 Rice 1993 Roadside 1994 Barley, wheat 1996 Rice 1997 Rice 1997 Rice 1998 Almonds, roadsides 1998 Rice 2000 Rice 2000 Rice 2000 Sugar beets, onions 2001, 03 Rice 2002 Roadsides 2005 Roadsides 2005 Roadsides 2007 Roadsides, vineyard 2009
19 92
19 90
0
19 88
5
19 86
10
19 84
15
19 80
Number of Species
20
19 82
25
Common groundsel Perennial ryegrass Smallflower umbrella sedge California arrowhead Russian thistle Wild oat Redstem Ricefield bulrush Late watergrass Rigid ryegrass Long-leaved loosestrife Barnyardgrass Early watergrass Small-seeded canarygrass Smooth crabgrass Horseweed Italian ryegrass Hairy fleabane Hairy fleabane
www.weedscience.org Sept. 1, 2009
Factors Affecting Selection of Herbicide-Resistant Weeds Agronomic production practices Weed biology Herbicide properties
Agronomic Factors • Crop rotation – monoculture vs. short rotation vs perennial crops
• Tillage – direct seed and perennial systems must rely more on other methods of weed control
• Crop competitiveness – affects weed populations, which can affect selection of herbicide-resistant weeds
• Herbicide rotation (different modes of action) – Changes selection pressure
Occurrence of HRW in Field Crops ~# resistant biotypes Cereals 60 Corn 52 Rice 28 Soybean 24 Canola 11 Cotton 5 Sugarbeet 4 Group 1 resistant wild oat treated with Fusilade
Occurrence of HRW in Other Crops ~# resistant biotypes Vegetables 16 Orchard 37 Pasture 23 Forestry 8 Other perennial 8 (tea, coffee, rubber, mint, etc)
Non-crop (roadside, railway, industrial)
35
Weed Characteristics • • • • • • • • •
Annual growth habit High seed production Little seed dormancy Seed longevity in soil Original frequency of R trait in population Multiple generations per year Gene flow (pollen and seed) Fitness of R v. S biotype Highly susceptible to the herbicide
SU-resistant Russian thistle dispersal - Stallings et al. 1995
Propensity of a Species to Develop Resistance • Some species are more prone to develop herbicide resistance – – – – – –
28 spp. with resistance to 2 MOA 10 to 3 MOA 3 to 4 MOA 1 to 5 MOA 3 to 6 MOA 1 to 8 MOA • one rigid ryegrass biotype has resistance to 7 MOA!
Worst HRW Worldwide - based on # infested sites • • • • • • • • • •
Rigid ryegrass Wild oat Redroot pigweed Common lambsquarters Green foxtail Barnyardgrass Goosegrass Kochia Horseweed Smooth pigweed
Sept. 2009: www.weedscience.org
Worst HRW Worldwide - based on # infested sites • • • • • • • • • •
Rigid ryegrass Wild oat Redroot pigweed Common lambsquarters Green foxtail Barnyardgrass Goosegrass Kochia Horseweed Smooth pigweed
Think: • Annual growth habit • High seed production • Little seed dormancy • Seed longevity in soil • Gene flow • Highly susceptible to herbicide
Herbicide Characteristics • Single site of action Think: • Sulfonylurea in wheat/rice • High efficacy on a weed • Triazine in field and crops species – selection pressure • horticultural ACCase inhibitors in cereals • Long soil residual activity • Paraquat and glyphosate in orchards/vineyards • High use rate (relative to amount needed) • High frequency of use (yearly or multiple applications per year)
HRW can be a BIG problem - How do we prevent or manage it?
Prevention / Delaying Resistance • Reduce selection pressure! – Rotate herbicide mode-of-action – Use short residual herbicides?? – Tank mixes?? – Crop rotation – Multiple weed control tactics (tillage)
• Use good agronomic practices – Plant clean seed – Good record keeping – Control escapes
Rotate Modes of Action • Mode of action refers to the way that herbicides alter or inhibit specific physiological or biochemical processes – Examples include inhibitors of: ACCase, ALS, photosystem II, etc
• Not to be confused with: – Active ingredients – Trade names / product names See mode of action handout
Mode of Action Groups • Groups of ai and classes affecting the same target site WSSA group 9 = HRAC group G; – ALS inhibitors: SU, Imi, inhibition of EPSP synthase triazolopyrimidine, pyrimidinyl thiobenzoate, sulfonylaminocorbonyltriazolinone
• Two common systems: – WSSA (number system) – HRAC (letter system)
• Not all labels contain this info – Common in Australia and Europe – Work in progress in the US
Herbicide Selection • Avoid year-after-year use of the same herbicide or same mode of action • Short-residual herbicides? – Shorter length of selection (fewer generations) – However, avoid multiple applications per year
• Tank mixes? – Mixes intended to broaden spectrum may not reduce selection (grass plus broadleaf) – Addition of another product with activity on problem weed may help • But, may be better to rotate rather than tank mix (economics)
Crop Rotation • Allows growers to alter chemical and nonchemical methods – Crop selection – Tillage timing and choices – Planting dates – Crop competitiveness – Cultivation – Handweeding – Different herbicide choices – Not feasible in some situations (perennial crops, non-crop, rights of way)
Good Agronomic Practices • Avoid spreading weed seed – Weed-free seed, clean tillage and harvesting equipment
• Monitor weed control – Check for application problems and escapes – Hand weed or clean up weedy patches • before seed set!
• Keep accurate records – Herbicide modes of action used, application dates – Weed control failures – products, patterns, maps
Managing Resistance • Managing resistance once it occurs generally consists of “start doing the things you should have been doing to prevent/delay resistance” • Monitor for resistance and try to manage it as a small problem or patch rather than wait for a big problem
Identifying Herbicide Resistance NOT ALL ESCAPES ARE DUE TO RESISTANCE! • Field history – was same herbicide mode of action used long term? • Are other “susceptible” weed species controlled? • Were there application problems? • Are healthy plants intermixed with dying plants (of same species)? • Patch of an uncontrolled weed occurs in subsequent years and is spreading
Patterns to look for
Very possibly
Could be, but may just be escapes too
These two are not typical patterns associated with resistance
What if You Suspect Resistance? • Do not respray with the same or similar products • Consider reporting to researchers and saving seed for confirmation – However, better to control escapes before seed set!
• Develop alternative control strategy to manage the problem
Key Points on Herbicide Resistance • Herbicide resistance is a real and increasing threat to continued economic weed control in croplands and non-crop areas • Once resistance occurs, you lose the use of products the same mode of action for the foreseeable future • Development of new modes of action is slow due to reduced investment in herbicide discovery • Resistance management requires a multi-year plan that include resistance monitoring and rotation and/or mixtures of herbicide modes of action
More Information and Links • www.weedscience.org - International Survey of Herbicide Resistant Weeds • www.wric.ucdavis.edu – UC Weed Research and Information Center • www.plantprotection.org/HRAC - Herbicide Resistance Action Committee • ANR Publication 8012 – “Herbicide Resistance: Definition and Management Strategies” • www.wssa.net – Weed Science Society of America
Questions?