Management strategies help control resistant weeds

Herbicide-resistant weeds are becoming more of a problem, forcing growers to alter their weed-control programs. DuPont Pioneer agronomists say management decisions -- such as improved herbicide choices, clean seedbeds and careful planning for harvest -- can help decrease resistant weeds.

"Growers should attack problem weeds with multiple modes of action and multiple tactics," says Mark Jeschke, DuPont Pioneer agronomy research manager. "This will control more weeds and preserve effective herbicide technologies longer, giving growers more options."

A two-pass system of pre-emergence and post-emergence herbicides is another successful strategy for growers and is particularly effective for controlling broadleaf weeds that emerge early and grow rapidly. Split application is another emergence tactic, which boosts control and provides better residual activity to help combat late-season weeds.

Starting with a clean seedbed in the spring is also vital for reducing resistant weeds. While fall herbicide application can help control winter annuals, the value for summer annuals that emerge five or six months after treatment is questionable. A spring pre-emergence herbicide program can help further reduce resistance with a burn-down on the field.

"When using a pre-emergence program, growers should use the full rates recommended for these weeds," Jeschke says. "A good, broad-spectrum burn-down will clear vegetation and provide good residual activity to ensure weed control through planting."

Another approach growers can take to tackle weed resistance is by planning post-emergence applications earlier than previous years. Doing so attacks dominant weeds when they are three to five inches tall, an ideal growth stage, resulting in longer weed control.

Finally, before harvest, it's important both to assess the weed population of each field and to harvest heavily colonized fields last. This two-fold tactic avoids further distribution of weed seeds, which helps reduce the spread of resistant populations. Growers planning for the coming season can consult their Pioneer agronomists or sales professionals about developing a management strategy for herbicide-resistant weeds.