Soybean Aphids and Grasshoppers in Soybean
Posted: September 2, 2014
As we have noted in our soybean sentinel reports and previous issues of this newsletter, soybean aphids are present in Pennsylvania and quite common in some soybean fields, particularly in the northern half of the state. Populations remain spotty, with some fields having very few aphids, some fields approaching the economic threshold of 250 aphids per plant, and other fields have aphids but have healthy populations of lady beetle and other natural enemies that cause populations to crash. As we get later in the season, it is important to remember that soybean aphid is not economically significant past R6 stage beans, and many of our soybean are approaching or beyond R6 already. For further details, please see our fact sheet.
There are also soybean fields around the state suffering from grasshopper populations. Grasshoppers are not commonly economically significant for fields in Pennsylvania, but occasionally populations develop, particularly when it has been warm and dry, as has been the case for some areas. Grasshopper populations tend to develop first along field edges, and entire fields may not be afflicted. Economic thresholds for grasshoppers in corn and soybeans are poorly developed for the eastern US. Growers can use the informal range of 20-40 grasshoppers per square yard to help guide their treatment decisions. Organophosphates tend to provide less residual control against grasshoppers than pyrethroids. If weather continues to be hot and dry, insecticide use against grasshoppers has potential to flare spider mite populations, so if you decide to treat for grasshoppers, return to those fields regularly to watch for development of other pest populations. See the Penn State Agronomy Guide for insecticide options.