Grasshopper populations are elevated in Central South Dakota. Some of the concerns regarding these large grasshopper populations is that they are feeding on trees, gardens and almost everything in between. Typically, grasshopper infestations are worse in areas where dry conditions are being experienced. In a normal year, grasshoppers can be a nuisance in a garden but during an outbreak year they can be a real threat to gardens, shrubs, and small trees.
If grasshopper populations are causing severe defoliation in a garden, the use of a foliar insecticide may be warranted to protect the garden produce. Keep in mind, that many foliar insecticides labeled for grasshoppers are broad spectrum and can impact non-target insects like bees and other pollinators. When determining if an insecticide application is necessary, consider what plants are flowering and what parts of grasshopper targeted plants are being harvested for consumption.
Grasshopper feeding on small trees and shrubs should be closely monitored as this can seriously affect them. Treating the trees and shrubs may reduce the grasshopper feeding but this will only last as long as the insecticide residual. There are several products that can be purchased without a private pesticide certification for these uses. We are a little late in the season to apply insecticides to target grasshopper nymphs, but a general rule of thumb is that treating grasshoppers when they aren’t fully grown (1/2 to ¾ of an inch long) increases the chance of successful management.
In addition to spraying, watering areas around gardens and trees will slow down grasshopper feeding and help to eliminate any preexisting drought stress on the plants. Keeping green grass will encourage grasshoppers to feed there instead of on the garden plants. Also, by leaving a border of tall grass around the yard, the grasshoppers will have a food source and will not move into the rest of the yard as quickly.
To greatly reduce grasshopper populations in yards, the margins of the yard should also be treated. This would include road ditches and areas with tall grass or weeds. In all cases, make sure to read the labels and follow all label recommendations. As grasshoppers continue to reach adulthood, they will be harder to kill. It is ideal to manage them when they are nymphs.