Winter annual weeds are those species that germinate in the fall, go dormant over the winter and resume growth in late winter or early spring, then bolt and produce seed so that the species will survive to the next year.
The best time to control winter annual weeds is in the fall. This was covered in the October 14, 2005 CropWatch article, Spend less in the fall to control winter annuals, by Brady Kappler.
Since apparently there were a few who did not take Brady’s advice, I will discuss the next best option.
Rapid growth of winter annual grassy weeds starts when the soil temperature is above 40oF. Rapid growth of winter annual broadleaf weeds starts a little later in the spring, when soil temperatures reach 50-55oF. The most common winter annual broadleaf weeds in Nebraska include: marestail (horseweed), prickly lettuce, field pennycress, shepherdspurse, henbit, tansy mustard, blue mustard, and treacle mustard (bushy wallfower). In addition, dandelion and curly dock, which are not winter annuals, also are appearing. Also present in some fields are winter annual grassy weeds such as downy brome, jointed goatgrass, feral rye, and even volunteer winter wheat.
In Nebraska producers have found that no-till is an excellent means of conserving moisture in both irrigated and dryland fields. Winter annuals, however, can reduce the benefits of no-till by robbing the crop of valuable soil moisture which can limit yields. In heavy stands winter annuals can make planting or seeding difficult and even result in poor crop germination when they reduce soil water levels. Benefits from no-till include reducing the evaporation in evapotranspiration (crop water use). This can amount to 2.5 to 4 inches of water under center pivot irrigation plus the soil water lost from each tillage operation which can amount to 0.33-1.0 inch per pass, depending on depth of tillage. Also under no-till the soil water intake is increased. In fact, irrigators can benefit more in water savings than drylanders since they are wetting the soil surface more frequently.
Many people wonder why winter annual weeds have become more of a problem in recent years. With more growers planting Roundup Ready crops, there is less herbicide residual to control these weeds. When conventional crops were planted, the herbicide program provided residue to keep many winter annuals from germinating or growing in the fall.
In the spring, treatments should be applied as soon as temperatures are warm enough for plant growth. Several products will control winter annuals so consider which ones are likely to perform best in your situation. Some of these herbicides are listed in Table 1 and Table 2. Always check labels and for additional information and see EC130, 2006 Guide For Weed Management In Nebraska.
Bob Klein
Extension Crops Specialist
West Central REC, North Platte
|
 | ||
| Published by University of Nebraska-Lincoln Extension in the Institute of Agriculture and Natural Resources Cooperating with the counties and the U.S. Department of Agriculture. | ||
| The University of Nebraska-Lincoln does not discriminate on the basis of gender, age, disability, race, color, religion, marital status, veteran's status, national or ethnic origin, or sexual orientation. | ||