Herbicides are used to manage weeds by giving farmers more time to manage weeds, less soil disturbance and a high efficacy against target weeds. This system is relatively simple for weeds to overcome through resistance.
According to the USDA's Economic Research Service, herbicides resistance can cost the farmer anywhere from $20 to $60 or more per acre.
So what causes resistance?
Herbicides have not caused weed resistance issues; rather, natural mutants in a weed population that carries a gene making the weed resistant to the herbicide product that is being applied. With repeated use of a single herbicide group, selection pressure is put on the weed population for the mutant weed with resistance to persist and multiply. If the same product is used repeatedly, resistance will develop.
The following are a few tips in helping prevent herbicide resistance.
Know your enemy. What are the problem weeds on your farm? By knowing what weeds are a problem on your farm you will be able to develop a herbicide program that will work against your problem weeds.
Understand the difference between Mode of Action (MOA) and Site of Action (SOA). MOA of a herbicide refers to the effect the herbicide has on plant growth. SOA refers to the specific location within the plant that the herbicide binds too.
Use multiple and effective sites of action. By using multiple herbicide groups that are effective towards your target weeds will help with delay or prevent resistance development. Also be sure to use the effective herbicide rates.
Timing is also a critical component. Newly germinating or small weeds are easier to kill than weeds over 6 inches in height.
Farmers need to be ahead of the game with weed management, whether its managing an existing weed or preventing a new resistance from becoming a problem. Other management practices could include: increasing crop competitiveness, rotating crops and using mechanical weed management.
Sources: Kansas Farmer. ISU Integrated Management
