Grasshoppers, corn earworm, and fall armyworm are above ground plant feeders that feed on leaves and pods. Early season defoliation generally does not noticeably affect yield loss. Substantial plant defoliation may occur before flowering and losses will be minimal. Manitoba Agriculture Food and Rural Initiatives (MAFRI) report that 50 per cent defoliation before flowering results in an average yield loss of only three per cent. As the soybean plant reaches the flowering and pod-filling stage, defoliation is a greater threat to yield and controls may be needed.
In some areas, seed corn maggots may be found feeding on the seeds, which may affect seed germination and also produce weak seedlings that do not survive. It is rarely a problem except with poor weather conditions or if seed quality delays seedling emergence. Wireworms may also cause some damage to seedlings in localized areas as do white grubs.
Cutworms have reportedly been a problem in Saskatchewan whereby damage they cause can reduce plant stands considerably. Aphids have also been reported to cause damage to soybean when found in sufficient numbers. Aphids numbering more than 250 per plant in growth stages R1-R4 and found increasing beyond in growth stages R5-R6 with moisture stressed plants and few predators should be controlled.
For a list of registered insecticides available to control insects in soybean please see the most current issue of the Saskatchewan Ministry of Agriculture's Guide to Crop Protection.
Information adapted from the Saskatchewan Ministry of Agriculture.