No. 10 Article 8/June 1, 2007

Control of Volunteer Glyphosate-Resistant Corn in Soybean

Farmers can select from several herbicide options that provide good to excellent control of volunteer corn in soybean. Generally, more complete control of volunteer corn is achieved with postemergence soybean herbicides than with soil-applied products. Complete control of clump corn is sometimes more difficult to achieve than control of individual plants because thorough coverage of "clump" plants can be tough to accomplish.

The postemergence grass control herbicides Assure II, Fusion, Fusilade DX, Select, Select Max, Poast Plus, and Poast are very effective against volunteer corn, including volunteer glyphosate-resistant corn. It should be noted that control of volunteer corn with these herbicides may be reduced when the products are applied in combination with certain postemergence broadleaf herbicides. Other postemergence soybean herbicides that can suppress or control volunteer corn include Scepter, Raptor, and glyphosate. Scepter and Raptor will not provide much control of volunteer ClearField corn, and glyphosate will not provide acceptable control of volunteer glyphosate-resistant corn. Efficacy ratings, application rates, and volunteer corn heights for these products appear in Table 2.

We have conducted several field research trials over the years to evaluate various herbicides for control of glyphosate-resistant volunteer corn. These experiments have included soil-applied and postemergence herbicides, applied alone or tank-mixed (postemergence) with glyphosate. Results from many of these trials are included in Tables 3 and 4.

The results from the soil-applied experiments reinforce the prior comment that these types of treatments can provide some level of volunteer corn control or suppression, but acceptable control often requires supplemental management. Over the six-year period this experiment was conducted, the data for individual treatments often varied considerably, and not all treatments were included each season (Table 3). Many of the products included in this experiment are used primarily for control of broadleaf weed species, but all of these products did provide some level of volunteer corn control.

Several postemergence herbicides have provided excellent control of volunteer glyphosate-resistant corn over the duration of these experiments (Table 4). The ACCase-inhibiting herbicides (clethodim, quizalofop, fluazifop, sethoxydim) provide broad-spectrum control of grasses and are frequently tank-mixed with glyphosate for control of volunteer glyphosate-resistant corn. Keep in mind that spray additive recommendations for these products can vary depending on how the product is used (alone or in a tank-mix) or the type of glyphosate formulation it is tank-mixed with. For example, additive recommendations can vary if a product is tank-mixed with a glyphosate formulation containing a "built-in" adjuvant system or with a glyphosate formulation that itself requires additional surfactant.--Aaron Hager

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