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Recent rains help weed control applications
By D. Bruce Bosley
Extension Agent/Cropping Systems
Colorado State University Cooperative Extension
Many perennial plant species are vulnerable to weed control measures when they are going into their flowering stage of growth. Herbicide applications work best when applied to the many weed species at flower bud stage or, at the very latest, early flower stage. These include field bindweed, Canada thistle, diffuse, Russian, and spotted knapweed, leafy spurge, and in rangeland, cactus, and sand sage. Russian olive can also be controlled with herbicides applications at this time. In addition, musk thistle and some other biennial plants are controlled at or just prior to the early bolting stage of growth.
The recent rains will help weed control applications be effective because the target weeds will be rapidly growing and have open leaf pores.
Take care to avoid pesticide drift with any herbicide application. Most of the phenoxy class of herbicides, such as 2-4,D and dicamba have label use restrictions when daily temperatures are expected to exceed 85 degrees Fahrenheit. These chemicals produce vapor drifts that are prone to injure neighboring crops, trees, and landscape plants at high temperatures. Even when these herbicides are applied in the cool of the morning, toxic chemical vapors will lift off later on a hot day and can drift to neighboring fields. Each year I find evidence of phenoxy herbicide injury on sensitive crops near or even miles away from treated fields. Similarly, I often see injury on garden vegetables, trees and shrubs related to herbicide volatility drift. Therefore always read and follow label instructions on all pesticides.
Farm managers should also follow the label instructions when applying postemergence herbicides on corn and other field crops so that they will kill the weeds and not damage the crop. Many herbicides also need chemical adjuvants in the tank mix to make them work properly. For instance, adding a 1 to 2 percent solution of ammonium sulfate makes Glyphosate-based herbicides work just that much better.
People can learn about weed control and many other aspects of dryland cropping systems at next week's USDA-ARS Central Great Plains Research Station field day at Akron. The field day starts at 7:30 a.m. on Wednesday, June 15. Lunch and refreshments will be provided courtesy of the research station.
The Akron field day is also one stop of the Colorado Wheat Field Day circuit. The Wheat field days start in northeast Colorado on June 14, near Burlington at the Randy Wilks Farm at 4 p.m. The Yuma event takes place at 4 p.m. on June 15 after the Akron Research Station field day. June 16 marks the field day at Julesburg and Orchard, at 8 a.m. and 12:30 p.m. respectively. Finally, June 20 is the day when we will be hosting the Bennett field day. All Colorado Wheat Field Days will include a complementary meal provided by the Colorado Wheat Administrative Committee and local sponsors. Contact your local Extension office for times and directions.
Please contact me, if you have questions (522-3200, ext: 285).
Date: 6/23/05
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