Title: Herbicide Tolerance
1Herbicide Tolerance Resistancein common
roadsideplants
2Herbicide Tolerance
3Herbicide Resistance
- When plants are no longer controlled by a
previously effective herbicide due to biochemical
changes in resistant biotypes - There are more than 230 resistant species
documented world wide
4There are weeds resistant to these herbicide
families
- Aryloxyphenoxypropionates (Poast)
- Cyclohexanediones (Envoy)
- Dinitroanilines (Surflan)
- Imidazolinones (Arsenal)
- Sulfonylureas (Oust)
- Triazines (atrazine)
5Weed Characteristics Favoring Resistance
Development
- Prolific seed producer
- High germination rate
- Extended germination period
- Highly susceptible to the herbicide
6Herbicide Characteristics Favoring Resistance
Development
- Single site of action
- Very effective
- Long soil residual
- High use rate
- High use frequency
7Cultural Practices Favoring Resistance Development
- Growing or managing the same crop year after
year - Seed production from escapes
- Using herbicides with the same mode of action
8Managing Resistance
- Change management program (rotate crops)
- Rotate herbicide families
- Use herbicides with a different
mode-of-action - Use mixtures with different
modes-of-action
9Managing Resistance
- Control escaped weeds in clear zones
- Prevent the spread of resistant weeds from clear
zone areas to transition areas (backslopes, wide
ROWs, interchanges) - Use weed management methods other than herbicides
(mowing, weedeating, etc.)
10Resistant Weeds
- Weeds that used to be controlled by a
herbicide but are now tolerant - Typically require a dose several times that
normally needed for control - May not be controlled at any dose level
11Resistant Weeds in Oklahoma
- Triazines - smooth pigweed
- DNAs - palmer pigweed, goosegrass
- Grass herbicides -
- johnsongrass (Fusilade)
- ryegrass (Illoxan)
- Arsenicals - cocklebur
- Amides - barnyardgrass
- ALS inhibitors - cocklebur, palmer pigweed
12Carefully diagnosis resistance
- Herbicide failure due to
- environmental conditions
- weeds that are too large
- poor application technique, rate, timing,
coverage, etc. - may be blamed on herbicide resistance
13Herbicide Resistance
- The first herbicide resistant weeds in the United
States were discovered in the 1960s in a pine
nursery in which triazine herbicides were used
repeatedly
14Conventional Wisdom
- Weeds do not mutate or change to become
resistant, but populations change - The resistant weeds have always been present at
low populations - As the normal types are removed the population of
resistant weeds increases
15Development of a Resistant Population
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Year 1
Year 2
Year ?
X susceptible
O resistant
16Things to Look For
- One weed, which normally should be controlled, is
not controlled although other weeds are
controlled - A patch of uncontrolled weeds is spreading
- Healthy weeds are mixed with controlled weeds of
the same species
17Resistance Mechanisms
- Target site changes
- Enhanced metabolism of the herbicide
- Changes in uptake and translocation
18Mode-of-Action ALS Inhibitors(acetolactate
synthase enzyme)
- Enzyme found only in plants
- Resistance to these herbicdes appeared within 5
years of their introduction into the market place.
19ALS Roadside Herbicides
- Oust (sulfometuron)
- Escort (metsulfuron)
- Telar (chlorsulfuron)
- Outrider (sulfosulfuron)
- Arsenal (imazapyr)
- Plateau (imazapic)
20Oust-Resistant Ryegrass
- Oust resistant ryegrass found along Mississippi
highways - Caused by use of Oust for winter annual weed
control and summer johnsongrass control
21Oust-Resistant Ryegrass (Mississippi)
22Cross Resistance
- ALS resistant plants are resistant to other ALS
herbicides but not all - Example Mississippi Scepter resistant cocklebur
were susceptible to Classic (another ALS
inhibitor) - Missouri - Scepter resistant cocklebur were
resistant to Classic and Broadstrike (before it
hit the market)
23Mode-of-Action ACCase inhibitors(acetyl
coenzyme A carboxylase)
- Resistance with 5 years of 1st appl.
- Johnsongrass resistance in Arkansas
- Crabgrass resistance in northern states
24ACCase Agronomic Herbicides
- FOPs
- Fusilade
- Assure
- Acclaim
- Illoxan
25ACCase Turfgrass Herbicides
- Illoxan (diclofop)
- Acclaim Extra (fenoxaprop)
- Vantage (sethoxydim)
- Fusilade (fluazifop-methyl)
- Envoy (clethodim)
26Triazine Resistance
27Triazine Resistance
28Roundup Resistance
- Roundup resistant ryegrass
- found in Australia. Survives up to 5 times the
normal rate. - Dont forget Roundup resistant genes they are
putting into crops these days (cotton, soybeans,
corn)