A common question asked last winter was a glyphosate herbicide can be mixed with an insecticide to kill bean leaf beetles and weeds with a single application. This question is a logical question because many growers are seeking to implement the old saying of "killing two birds with one stone." If you planted a Roundup Ready® soybean variety, then the answer is probably "yes." You must follow the product fact sheets and product labels for further information on tank mixing of the two pesticides that you select. But most bean leaf beetle insecticides probably can be mixed with most formulations of glyphosate, whether they are generic formuations or Roundup WeatherMAX, UltraMax, Original, or Custom.
A more relevant question is, "Would my soybean benefit from a tank-mixed application of both the insecticide and herbicide?" From the insect aspect, bean leaf beetles are best controlled when soybean plants are very small, that is, during soybean emergence (VE) to first trifoliate (V1) stage. From the weed aspect, and depending on the weed species involved, the glyphosate label will probably recommend that weeds are best controlled when they are 2 to 8 feet in height. The problem is that these two biological events, early soybean growth stage with bean leaf beetles and weeds that are the correct height, may not coincide in the field. Thus, when it is time to spray bean leaf beetles it may be too early to spray the weeds. Conversely, when it is time to kill the weeds it may be too late to spray the beetles and get the maximum benefit from the insecticide. If the field situation does match the right conditions so that you control both with a single tank-mixed application, then the soybean should benefit from this procedure.
This article originally appeared on pages 71-72 of the IC-490 (9) -- May 19, 2003 issue.