The Enid News and Eagle, Enid, OK

January 5, 2013

Residual herbicide helps keep fields clean

Enid News and Eagle

ENID, Okla. — Across northwest Oklahoma, residual herbicides have become the standard recommendation of Oklahoma Cooperative Extension Service ag educators and other crop consultants.

Oklahoma State University research has indicated adding a residual herbicide to producer’s herbicide program aids in keeping fields clean longer and free of yield robbing weeds and to improve weed resistance management practices. Simply put, a residual herbicide is a smart and valuable investment for today’s crop producer.

In 2013, producers should base their residual herbicide selection on several areas of performance. Areas that producer should consider include length of residual, application timing, spectrum of weed control, resistance management and crop rotation flexibility.

Length of residual

Some herbicides marketed as “residuals” may have a limited residual control and may become ineffective as the season evolves and tough weed pressure increase.

Residual products will range from a few days of control to several months of control. Most researchers agree four weeks is a realistic amount of control, but six weeks would be better. If you could get four weeks of residual control, the rest of your herbicide program could include a pre-emergence and one post-emerge spray. If you only get two weeks of control from your residual herbicide, you will likely add an additional post-emerge application.

Application timing

Crop rotation, weather trends and even producer preference weigh on the minds of producers with timing their herbicide program. A highly flexible residual herbicide program will allow a producer to apply anytime from post harvest applications to pre-emergence applications.

Recent OSU work has indicated a fall/winter residual herbicide program has worked well on tough to control weeds like marestail and kochia. Other advocates of this practice mention ridding fields of nutrient- and moisture-robbing winter weeds are important.

Others like the thought of having some weed control in place in case spring time weather patterns limit chances of the spring time burndown residual application.

The most popular time to apply a residual herbicide is in the spring, several days or weeks before planting. Most producers use this practice because application timing allows the longest period of residual weed-killing activity through the planting season.

Spectrum of weed control

The primary reason for using an herbicide product is to control weeds. It is imperative producers look for a residual herbicide that will control the weeds problematic within their fields. In the long run, it is more economical and timely for producers to use a residual herbicide able to control both broadleaves and grasses with little to no chances of a breakthrough.

Resistance management

Not long ago, “resistance” was a problem most producers assumed was happening in someone else’s field. Resistant or even tolerant weeds are now becoming a major issue in weeds across northwest Oklahoma. OCES ag educators and other consultants now suggest controlling these weeds with a comprehensive herbicide program that includes residual herbicides and others modes of action before the problem grows to large to deal with.

Research indicates that by applying a residual herbicide, producers can extend the window for putting on post-emergence herbicides to reduce yield losses and also reduce our worst weed problems to a glyphosate product.

Crop rotation flexibility

Crop rotation is widely considered as one of the best ways to keep a field healthy and reduce weed pressures. Therefore, a good residual herbicide program must be designed to work well with a variety of possible crop options.

Recently, producers are finding even the best laid plans for cropping change unexpectedly. Erratic springtime weather and dry, hot summers with little rainfall have numerous local producers abandoning their production patterns. Rotational flexibility is an increasingly key component to consider in a residual herbicide plan.

All residual herbicides are not created equally. But by understanding the specific needs and weed pressure of a producer and by analyzing residual herbicides based on a few key factors, a producer can make and educated decision on which residual herbicide to choose to maximize their profit and minimize risks.

Gribble is Oklahoma Cooperative Extension Service northwest area agronomist.