Weed Control With Paul Baumann: Texas

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Common waterhemp, Palmer amaranth and sharppod morning glory are predicted to be difficult weeds for growers to manage across cotton fields this season in Central and Southeast Texas. Dr. Paul Baumann, Professor and Weed Specialist with Texas A&M AgriLife Extension, explained how critical it is to spot and stop these weeds early in the growing season. If just one weed spreads seeds, growers could experience severe weed issues in their cotton acres for years to come. During a recent interview, Baumann recommended starting with a soil-applied herbicide prior to emergence to protect yield potential and manage resistant weeds.

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Question: What are the major tough-to-control weeds in your area?

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Baumann: For the most part, the problem weeds in Central and Southeast Texas are common waterhemp and Palmer amaranth. We also have sharppod morning glory and that’s about it in terms of weeds that are a real issue. In other areas of the state, silverleaf nightshade (whiteweed) and woolyleaf bursage (lakeweed) can be a problem, but those have been pretty well managed with Roundup® agricultural herbicides over the years.

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Question: What makes common waterhemp, Palmer amaranth and sharppod morning glory such an issue in your area?

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Baumann: In the case of the common waterhemp and Palmer amaranth, the largest issue is seed load since they can produce a half million seeds per plant. If any of those weeds elude effective herbicide treatment, even if it’s just one plant per acre, this can cause real problems the next year in terms of infestations. Sharp pod morning glory is a problem because it’s a perennial weed. You can’t control them with any preemergence herbicides because much of their development comes from previously established rootstock that has been cut up and transported through the field. Only the seeds and not the root pieces are susceptible to preemergence herbicides. The same can be said for silverleaf nightshade and woolyleaf bursage.

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Question: How would you recommend controlling these weeds?

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Baumann: If they’re not resistant, we’ve had great success with many of the soil applied herbicides and post-emergence herbicides including Roundup agricultural herbicides. In the case of the perennial weeds, repeated applications of glyphosate during the year have made dramatic improvements in management. Applications of glyphosate, tank-mixed with an additional effective mode-of-action, have helped in managing these tough-to-control weeds.

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For more information on Roundup Ready PLUS® Weed Management Solutions on tank mixing go to Weed Manager PLUS app.

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Question: When giving advice on control, what is the first step you communicate to growers?

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Baumann: Starting clean is key, so it is recommended that growers eliminate any weeds prior to planting. Then, start with a soil-applied herbicide, whether it’s a preplant or preemergent herbicide. This has two benefits. One is that preemergent herbicides are generally very effective for controlling common waterhemp and Palmer amaranth, especially in cotton. The second benefit, which is often overlooked by many growers, is the importance of managing early season weeds to eliminate their competition with the crop. Our growers have been used to seeing highly effective control of weeds in various stages of growth and have not been so concerned with weed competition within the first few weeks after planting. It has been shown that the ten weeks after the crop comes up is critical in terms of eliminating the competition for weeds. Even if you don’t have a resistance issue in your field, the use of a soil-applied herbicide is going to be a benefit managing that early season competition and preserving yield.

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Question: Why is it so important to control these weeds before they reach four inches in height?

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Baumann: Most products, not including Roundup agricultural herbicides, are going to be the most effective if applied before that. The Roundup agricultural herbicideslabel allows some flexibility in treatment timing by adjusting the application rate to the size of the weed. It’s going to be difficult to control 10-12 inch weeds with any product. If you don’t control glyphosate-resistant weeds prior to four inches, there are not many options available that will manage weeds larger than that. Part of the whole management problem is that by the time you see those escaped weeds, often times the grower will assume he just missed them with the spray boom. Then, they’ll spray again and by now the weeds are 12-14 inches tall. At that point, there’s not much you can do besides hand pulling, and in some cases, cultivate between the rows.

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Baumann: If the weed came up early enough and sheds seeds, those seeds could emerge later in the season. Even more likely though, the escaped weeds will shed seeds this year that will be dragged through the field with tillage equipment, causing issues next year and for years to come.

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Question: How have resistant weeds changed the way growers put together their management plan?

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Baumann: The biggest thing it has done is shown growers they have to be more observant of what is going on in their field in terms of weed management. If growers have an amaranth species (Palmer amaranth or common waterhemp), it is absolutely critical to remove them. Growers need to get out of the truck, jump off the spray rig or cultivator and pull them up because if they’ve been using any herbicide labeled for control, which includes glyphosate, there is a reason it is still out there. There’s likelihood that it is a resistant species and could shed more than half a million seeds and cause a lot of problems later in the season.

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Question: Where do you see the future of weed control if we continue down our current path?

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Baumann: It’s going to require more diligence in scouting fields than we’ve been accustomed to in years past. Essentially, with the high degree of effectiveness of Roundup agricultural herbicides and other products, growers were confident that once they’ve sprayed, the job was done. Now they’re going to have to go back and make sure they don’t have any escapes, and if they do, be very timely with remedial applications after that. If herbicide manufacturers continue to come out with new chemistries that will be effective for managing resistant weeds, or transgenic technologies that allow for use of alternative products, our problems with resistance could be alleviated. It is also dependent upon our growers to follow recommendations for resistance management to avoid or eliminate the occurrence of herbicide resistant weeds in their fields.

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It is critical to get these weeds under control early in the season. If not treated in a timely manner, these weeds could compete with the crop for essential nutrients reducing yield potential. Baumann highly recommends utilizing a soil-applied herbicide prior to emergence for adequate control. To get regionalized crop recommendations, click here to visit roundupreadyplus.com.

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