Reliance on postemergence herbicides has lead to resistance,
calling for the return of residual herbicides to
By Dr. Jason Ferrell
The 1990s proved to be an era when postemergence herbicides with unparalleled efficacy and crop safety entered the market. These new postemergence herbicides controlled a wide variety of weeds, and in some cases, even provided lengthy residual control. No longer were producers required to apply herbicides at planting, perform in-season tillage or spray postemergence herbicides on extremely small weeds.
But just as the 1990s will be remembered as the decade of new postemergence herbicides, the 2000s will be known as the decade of resistance.
Time and experience have taught us that opposition to change is a recipe for resistant weeds. A diverse herbicide strategy that utilizes multiple mechanisms of action is now required, regardless of whether resistance is currently present.
The best way to develop a more diverse herbicide strategy is to resume use of the highly effective preemergence herbicides that are available (see table). Not only will these herbicides provide effective weed control, but many have a low probability of resistance. Although these herbicides may require a greater investment “up front,” they will pay great dividends by preventing resistance and providing excellent weed control.
Unlike the postemergence herbicides, most soil-applied herbicides
must be activated to work. A rainfall or irrigation of .5 to 1 inch is
needed within seven to 10 days after application. Dryland peanut fields
should not be treated with a soil-applied herbicide if there is no possibility
for rain within seven days of application.