Soybean Insect Update

Bryan Jensen, Dept. of Entomology and IPM Program

So far this summer, soybean insects have been relatively quiet. However, there have some reports of soybean aphids increasing. That may not be too surprising based on recent weather trends but hot weather is predicted and may slow aphid population growth. Also, in some areas of the state it has been relatively dry and it makes me a suspicious about the potential for two-spotted spider mite infestations. Populations of both pests really need to be considered before making a spray recommendation. Please be aware that spraying soybean aphids at below threshold levels will not recover applications costs and potentially could drive mite populations up. Especially if dry conditions continue. If soybean aphid populations do reach threshold levels and there are signs of active mite populations in the field choosing a product that is active on both pests should be considered. Please consult A3646, Pest Management in Wisconsin Field Crops for insecticide/miticide recommendations. Be sure to monitor populations in the sprayed fields after the restricted entry interval (REI) has been met. Killing 90% of a pest means 10% are still living. For spider mites the insecticide/miticides do not control eggs. Killing beneficial insects with an insecticide application can “release” a pest population and rebounds are possible.

Japanese Beetles and/or their damage have been noticed by a lot of people this summer. However, it takes a lot of feeding to cause economic damage. For soybeans in the reproduce stages need an average of 15-20% defoliation on a whole plant basis before economic damage is realized. Before considering an insecticide application, I would have the same caution about spraying below threshold levels. Do consider the possible impact on both soybean aphid and spider mite populations.

How long will Japanese Beetle populations be around? Typically by the time we reach mid-August you can notice an overall drop in adult numbers.

Early symptoms (stippling) of twospotted spider mite damage