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Corn+Soybean Digest

Weed Management Essential

A good weed-control program, which includes fall herbicide applications, is essential to produce profitable high wheat yields. Weeds can reduce yields by 50% or more by competing for nutrients, sunlight and moisture. They also reduce your profits by contaminating your grain with seed, which results in dockage and a reduction in price at the elevator.

Survey wheat fields (in the southeast and other areas) and you will likely find many different weed problems such as wild radish, wild garlic/onion, annual Italian ryegrass, common vetch, henbit, chickweed, curley dock and little barley. In the spring you may also see common ragweed, cutleaf evening primrose, pigweed and thistles.

However, the most problematic weeds (in Georgia, parts of the South and other areas) are wild radish, wild garlic and annual Italian ryegrass. These weeds can reduce your yields over 50% if left uncontrolled. Therefore, it is important to control these weeds effectively and efficiently.

When to apply herbicide
“My preference is to treat for weeds in late fall and early winter to tackle weeds at a younger age,” says Dewey Lee, University of Georgia Extension agronomist. “Our biggest problem is we get a run of late emerging ryegrass. If growers don’t start weed control early enough, they can see more reduction in yields and efficiency.”

Growers know that controlling weeds in wheat may be one of the most difficult management practices in cultivated crops. Timing is critical because weather-related problems often interfere with applications. Delayed chemical applications increase the cost of weed control simply because herbicide rates have to be increased as weeds grow larger with time. This can reduce control because winter weeds are more difficult to control as they get larger.

Some producers stretch the window of application too wide, which results in poor weed control and crop injury. Wheat plants are very susceptible to injury by some herbicides as they enter the reproductive phase. Planning ahead will prepare you to take advantage of the options available during the growing season.

The key factors in a good weed-control program are: 1) recognizing your weeds, 2) choosing the right herbicides, 3) timing the application for best control of the target weed by adjusting for crop growth stage, 4) using the correct rate and 5) reading and abiding by all label restrictions.

Cultural weed management is probably the single most important factor in reducing weed pressure in wheat. Using certified seed ensures quality, weed-free wheat seed. Proper seedbed preparation, fertilization and insect and disease control help ensure a healthy crop and allow the wheat to shade the soil surface and out-compete many weeds.

Site selection can play a significant role in wheat weed control. Rotation away from fields with heavy infestations of weeds common to your area will aid weed control. In addition, this allows for alternative crops and control methods (herbicides) that can reduce the populations of these weedy species. This also reduces the development of herbicide-resistant weeds.

Once wheat has begun to germinate, it is necessary to properly identify the weeds. This should occur soon after the weeds emerge because larger weeds are harder to control (sometimes impossible) and will have already caused some yield loss.

The stage of development of the wheat plant, particularly with regard to tillering is an important factor in chemical weed control. Many herbicides used in wheat can only be applied during certain stages of wheat development to avoid crop injury. Many of the herbicides used on wheat affect the growth of the target weed, either through physiological or metabolic mechanisms. Therefore, the better the plant is growing, the better the control.

For more on weed control from your region, see your regional Extension wheat or grains specialist or visit their Web site. For more on southeastern area wheat weed control, go to College of Agriculture & Environmental Sciences.

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