Raptor (imazamox) plus Basagran (bentazon) is one of the most popular post-emergence herbicide treatments applied to dry edible beans. One of the main purposes for adding Basagran to Raptor is to “safen” (decrease crop response) dry beans from Raptor applications alone. At least 8 fluid ounces per acre of Basagran 4L is needed to safen dry beans from Raptor applications. However, increasing the Basagran 4L rate to at least 16 fluid ounces per acre has helped improve common lambsquarter control and has provided additional control of common cocklebur and jimsonweed without increasing dry bean injury. This combination applied with a crop oil concentrate (1 percent v/v) and ammonium sulfate (12-15 pounds per 100 gallons) or 28 percent UAN (2.5 percent v/v) has been standard for many years.
However, this year it looks like Raptor will be in short supply for post-emergence weed control in dry beans. One option growers have is to use the new herbicide pre-mixture, Varisto 4.18L. Varisto is a pre-mixture of Raptor plus Basagran. The standard application rate of Varisto is 21 fluid ounces per acre, which is equivalent to 4 fluid ounces per acre of Raptor and 21 fluid ounces per acre of Basagran 4L. A crop oil concentrate (1 percent v/v) and a nitrogen source (ammonium sulfate at 12-15 pounds per 100 gallons or 28 percent UAN at 2.5 percent v/v) should be included with post-emergence Varisto applications.
The application window for Varisto is between one fully expanded trifoliate up until dry beans start to bloom. Severe crop damage and yield reductions may occur if Varisto is applied outside of this application window. The pre-harvest interval for Varisto is 30 days.
In 2013, we conducted weed control and crop tolerance studies with Varisto and found weed control and crop safety similar to the tank-mixture of Raptor plus Basagran at equivalent rates. Dry bean yields were also similar to our weed-free control. One important thing to keep in mind is the crop rotation restrictions for Varisto will be similar to the Raptor plus Basagran tank-mixture: three months for wheat and alfalfa, 8.5 months for corn and 18 months for sugarbeets (soil pH greater than or equal to 6.2).
Source: Christy Sprague, Michigan State University