Issue No. 3, Article 5/April 13, 2007
Controlling Winter Wheat
The recent period of cold temperatures has taken its toll on the winter wheat crop in many areas of Illinois. Reports range from minimal to significant damage of existing stands, prompting many to consider abandoning the wheat crop in favor of corn or soybean. If the decision is made to plant corn or soybean into stands where some wheat plants remain alive, it is advisable to control them before planting either corn or soybean. Controlling existing wheat stands can be accomplished through the use of tillage, herbicides, or a combination of the two. Some considerations and suggestions that might improve overall control follow.
- If the wheat field was previously treated with a herbicide, be sure to check for any applicable crop rotational intervals. If you suspect a rotational interval has changed for a particular herbicide, it might be wise to check with the product manufacturer for the most current information.
- If a combination of herbicides and tillage will be used, improved control of winter wheat might be achieved if the herbicide application occurs prior to the tillage operation, compared with the opposite order. Regardless of the herbicide you use to control surviving wheat plants, there should be an interval of 3 to 5 days, or more, between application and tillage to allow the herbicide to work within the plant.
- If a herbicide will be applied without subsequent tillage, overall efficacy might be improved if the applications are delayed until sustained periods of warmer air temperatures. Herbicide activity, especially activity of translocated herbicides, is generally reduced when daytime air temperatures do not exceed about 50 degrees, or when nighttime air temperatures are about 40 degrees or below.
- It is altogether possible that other weed species, such as maturing winter annuals, early summer annuals, biennials, or perennials, may also be present in existing wheat fields. If so, select a herbicide or herbicide combination that will provide broad-spectrum control of both grass and broadleaf weed species. If 2,4-D is included in the tankmix, be cognizant of the intervals that must elapse between application and planting (especially for soybean, but also for corn with some formulations).
- The labels of the ACCase-inhibiting herbicides (Poast Plus, Assure II, Select Max, Fusilade DX, and Fusion) indicate that these products are effective against volunteer wheat. However, each product label also indicates a specific rotational interval between application and planting corn. Poast Plus is labeled for preplant applications, but applications must be made at least 30 days before corn planting. The labels of Select Max, Fusion, Fusilade DX, and Assure II indicate rotational intervals of 30, 60, 60, and 120 days, respectively, between application and corn planting.
- Gramoxone Inteon is a rapidly acting herbicide, especially when the application is followed by several days of bright sunshine. Efficacy on wheat can be improved when atrazine or metribuzin is tankmixed with Gramoxone Inteon. A crop oil concentrate or nonionic surfactant should be included, and thorough spray coverage is essential for good control. Activity of Gramoxone Inteon plus atrazine can be increased when applied with a high concentration of UAN solution. Other atrazine-containing premix products may also be good tankmix partners with Gramoxone Inteon.
- Glyphosate is very effective on grasses, including wheat. The label suggests using 0.75 lb ae to control overwintered wheat that is 12 inches high or less. Increase the rate to 1.125 lb ae for wheat up to 18 inches high. Several herbicide premixes contain glyphosate, and some of these products can be used to control existing vegetation and provide some soil residual activity. Be sure to include a nonionic surfactant if the formulation is a "nonloaded" one, and consider using straight ammonium sulfate instead of blends or replacement products, especially when hard water is used as the carrier.
- Controlling wheat plants after corn emergence might be more challenging than controlling these plants before planting. Glyphosate, used in conjunction with glyphosate-resistant corn hybrids, could be an effective option to control wheat plants that remain following corn emergence. Products containing nicosulfuron, foramsulfuron, or rimsulfuron can provide some suppression or control of wheat when applied postemergence in corn.