Don’t Exceed Maximums in Roundup Ready Soybean

Chris Boerboom, Extension Weed Scientist 

As some of the second applications of glyphosate that are being made, it might be time to review a couple maximums with glyphosate.

Glyphosate labels specify that glyphosate can be applied to soybeans through the flowering stage, which is equal to the R2 growth stage. The next growth stage is R3, which begins when one of the four top nodes with a fully developed leaf has a 3/16 inch long pod. Applications made to soybeans in the R3 stage would be considered off-label applications. Hopefully, weeds have been controlled prior to this stage. Adding glyphosate with late season insecticide or fungicide treatments would also be off-label if made after the R2 stage.

With second or even third applications of glyphosate to soybeans, we must also be aware of the maximum rates of glyphosate that can be applied in-season. The maximum rate for a single application in-season is 1.5 lb ae/a and the maximum for the total of all in-season applications is 2.25 lb ae/a. If we use a generic glyphosate (3 lb glyphosate/gallon) as an example, a maximum of 2 qt/a can be applied at one time and a total of 3 qt/a can be applied in-season. This could be applied as three 1 qt/a treatments or as a 2 qt/a plus a 1 qt/a application. If the example was a PowerMax or WeatherMax formulation (4.5 lb glyphosate/gallon), the maximum for a single application is 44 oz/a and the in-season total is 64 oz/a. For formulations with other concentrations, these maximums are listed on the glyphosate label. When dealing with certain tough weeds, the potential exists that these maximums could be exceeded if care is not taken, but a little planning will ensure the label is followed.