By: G. D. Morgan, Associate Professor and State Extension Cotton Specialist; A. Fromme, Assistant Professor and Extension Agronomist; A. Baumann, Professor and Extension Weed Specialist; Grichar, Senior Research Scientist; B. Bean, Professor and Extension Agronomist; E. Matocha, Extension Program Specialist; A. Mott, Extension Program Specialist–Cotton; The Texas A&M University System
The overwhelming adoption of cotton varieties that have singleand double-stacked herbicide-tolerant traits—including Roundup ReadyFlex®, LibertyLink®, GlyTol®, and GlyTol®/ LibertyLink®—has revolutionized cotton production in the past 10 to 15 years, and it offers some excellent weed management options to cotton producers. In Texas, over 90 percent of the cotton acres are planted to cotton varieties that include one or more of these herbicide-tolerant traits.
Despite the many opportunities that these traits provide for farmers, they do create challenges. For example, consecutive plantings of herbicide-tolerant crops can lead to herbicide-tolerant volunteer cotton, corn, or soybean plants; these volunteers meet the definition of a weed (an unwanted plant).
These volunteer plants can create problems for growers:
- They compete with the crop for essential nutrients, water, and light.
- They can cause harvest issues.
- Volunteer cotton plants can be difficult to manage in other crops such as corn, sorghum, soybeans, or wheat, depending on the herbicide-tolerant genes they contain.
- Volunteer cotton can serve as hosts for boll weevils (Anthonomus grandis L.) in grain crops and hinder the Texas Boll Weevil Eradication Program.
2011 and beyond
Between 2011 and 2013, stacked herbicide-tolerant varieties are expected to be widely available to cotton producers, including glyphosate + glufosinate-tolerant cotton varieties. Within the next 4 to 5 years, cotton varieties resistant to 2,4-D and dicamba are expected to be registered for use in the United States and available to producers as triple-stacked herbicide-tolerance traits.
This next generation of herbicide-tolerant cotton varieties will provide many weed management options as well as the flexibility to combat and retard the development of herbicide-resistant weeds. However, they will further complicate the issue of managing volunteer cotton in cotton-production regions.
Two major factors contribute to the need to remove volunteer cotton from Texas crops:
- Volunteer cotton can compete with the crop and reduce yield.
- The boll weevil eradication program may become less successful—primarily in South and East Texas, where the program is still active—due to the presence of plants that can host boll weevils.
From the crop competition perspective, most producers would consider 80 to 90 percent control by any herbicide to be acceptable. However, in quarantined zones of the boll weevil program (Fig. 1), there is a zero tolerance for volunteer cotton in non-cotton fields, also referred to as noncommercial cotton. In these quarantined zones, the Texas Department of Agriculture maintains zero tolerance for hostable noncommercial cotton plants (6 to 8 leaf plants or larger). Essentially, non-cotton fields must be kept completely void of hostable cotton plants for the entire year.
Although complete control is a challenge, it can be accomplished by choosing the appropriate herbicides and applying them at the proper time. This publication aims to help producers make decisions on herbicide use for volunteer cotton.
There are five key times during the year for managing volunteer cotton: fallow, preplant, preemergence, within season, and postharvest. The management strategies that are best for a specific site will depend on local weather patterns, crop rotation, tillage regime, and other factors. Although this publication focuses primarily on the herbicide options, growers should also consider tillage (disking or cultivation) to manage volunteer cotton.
Tillage: Tillage is one of the most effective tools for managing volunteer cotton in fallow situations or before planting any crop. However, in-season crop cultivation will leave about 15 to 25 percent of the area undisturbed, where cotton plants can survive. Although the 75 to 85 percent level of control should suffice for minimizing crop competition, it is unacceptable to the Texas boll weevil program.
Herbicides: Various herbicides can effectively control volunteer cotton during the fallow period and growing season. However, only a few herbicides specifically list management of volunteer cotton on their labels. For optimum results, follow the herbicide label instructions for rate, application timing, additives, carrier volume, and other factors.
Preplant burndown herbicides: Table 1 lists the herbicide products labeled for corn, sorghum, soybean, and wheat. Use Table 4 to estimate their effectiveness for postemergence.
Preemergence herbicides: See Table 2 for herbicides labeled in corn, sorghum, and soybean. The most effective preemergence herbicides will likely reduce volunteer cotton stands by only about 65 percent, and 2 pounds per acre of atrazine reduces stands by only 30 percent. See Table 5 for specific preemergence herbicide efficacy ratings. Although preemergence herbicides can help manage volunteer cotton, other tactics will likely be needed also.
Postemergence herbicides: See Table 3 for postemergence herbicides labeled in corn, sorghum, soybean, and wheat. The volunteer cotton plants must be small (1- to 4-leaf stage) for good to excellent control of volunteer cotton and for the most herbicide options. See the efficacy ratings in Table 4.
Once cotton reaches the 5- to 6-leaf stage or beyond, the number of highly effective herbicide options plummets because the cotton becomes much harder to kill. Also, none of the herbicides provide 100 percent volunteer cotton control when applied at the 5- to 6-leaf stage.
Hostable plants for boll weevil: Any cotton at pinhead square stage or beyond is considered hostable for boll weevils. This stage is when the Texas Department of Agriculture begins enforcing volunteer cotton guidelines. Volunteer cotton plants must be prevented from reaching this stage for the overall success of the Texas Boll Weevil Eradication Program and for growers to avoid fees or fines for volunteer (noncommercial) cotton found in fields.
To ensure that the herbicide is as effective as possible and to eradicate the plants that host boll weevils, volunteer cotton should not exceed the 5-leaf stage when the herbicide is applied. Cotton plants at or beyond the 5-leaf stage are very likely to survive the herbicide application and become hostable plants.
Mechanism of action: To manage volunteer cotton plants, growers must know the herbicide’s mechanism of action, because most cotton varieties have herbicide-tolerant traits. This information will be even more important as double and triple herbicide-tolerant traits are integrated into cotton varieties. Producers will have to consider the herbicide-tolerance traits in their cotton variety and select a herbicide with an alternative mechanism of action to control the volunteer cotton. For example, to adequately kill a cotton variety with glyphosate tolerance (Roundup Ready® or GlyTol®), it will need to be treated with a herbicide with a mechanism of action other than an EPSP inhibitor, such as a Liberty®, Gramoxone®, or others.
Herbicide options and disclaimer: The information in this publication is not a substitute for reading the label. It is meant to be a quick reference to identify potential herbicide options for controlling volunteer cotton. The information contained in this publication is based on many research trials conducted over the past several years by Texas AgriLife Extension and Research personnel. The trials evaluated many herbicides over a broad spectrum of environments and cotton growth stages.
Herbicide injury to corn, sorghum, soybean, or wheat from the herbicides listed in this publication was not evaluated and is not reported. Therefore, pay special attention to the application method (hoods, drop nozzles, post-directed) and timing for each crop.
Download a printer-friendly version of this publication: Managing Volunteer Cotton in Grain Crops
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