Weekly in-season Updates
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INFORMATION |
July 11, 2005 Talkin’ Cotton Late-season Weed Control Shane Osborne, Oklahoma State University
There is no doubt that when we talk about troublesome weeds in cotton the first weed that comes to mind is morningglory. Unfortunately morningglory has been the number one “most difficult to control” weed in cotton for a number of years. Fortunately, technology is lending a helping hand in managing this weed. Currently, the Roundup Ready cotton system, the Liberty Link cotton system and STAPLE herbicide are the most effective tools we have for managing early-season morningglory. However as we reach cottons blooming stage weed control strategies often change due to several factors. As a result of healthy plant growth and a developing canopy, good coverage from broadcast over-the-top applications becomes increasingly more difficult. This, coupled with the restriction on broadcast sprays over Roundup Ready cotton (4-leaf restriction), encourages the use of post-directed applications underneath the crop canopy. Regardless of whether you use a Wylie spray shield or a Redball 420 lay-by hood, the goal is to direct your application away from the crop foliage and on to the underlying weed population. Unless you planted Liberty Link cotton (which allows applications of IGNITE herbicide past the 4-leaf cotton stage without crop injury) your options are limited to either STAPLE herbicide or traditional post-directed applications. STAPLE is a very effective treatment for morningglory, however, broadcast applications may be considered expensive when applying the most effective rates. The standard for post-directed sprays for morningglory is probably still CAPAROL + MSMA, however, AIM is quickly becoming a standard for directed applications for morningglory in cotton. Tank-mixing AIM with either CAPAROL or DIREX (read and follow label restrictions addressing soil texture for both of these products) provides extremely good burndown combined with significant residual control. For those interested in using AIM there are some important requirements to remember. First, according to the label, cotton must be at least 12 inches in height and have sufficient bark development at the base of the stem. Do not allow the spray solution to contact cotton foliage or green stem tissue. A minimum of 10 gallons of water per acre is required and increasing this volume often improves morningglory control. Also, always include crop oil at 1% v/v (1 gallon per 100 gallons of water) with AIM lay-by applications. Another helpful hint is to slow your spraying speed down as much as possible. It is nearly impossible to make precision applications at 12 mph. Reducing your speed to 6-7 mph will usually increases your precision and in-turn the resulting weed control while reducing the potential for injury to the crop. The cost of one effective application is much less than trying to correct an error with a second trip. As always, reading and following product labeling is critical.
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