Watch for Grasshoppers

July 9, 1999

· Grasshopper nymphs have been seen in noncrop areas and alfalfa fields.

· Missouri entomologists have reported large numbers of grasshopper nymphs.

Redlegged grasshopper.

I received a couple of reports last week regarding grasshopper nymphs in noncrop areas (such as ditch banks and roadsides) and alfalfa fields. In addition, entomologists in Missouri are reporting that the numbers of grasshopper nymphs are quite high in several areas of their state. As you scout corn and soybeans for any number of insect pests, keep your eyes peeled for grasshoppers. The nymphs resemble adults, although they are considerably smaller at this time of year and they lack functional wings. Newly hatched nymphs lack wing pads, but larger nymphs usually have wing pads that develop into functional wings when they become adults (Figure 2).

There are two philosophies regarding control of grasshoppers. One approach is to treat noncrop areas while the nymphs are small and confined and before they begin causing injury to crops. The guidelines suggest treatment with an insecticide in these areas when the number of nymphs averages 15 to 20 or more per square yard. However, this approach does not allow Mother Nature to work her way with grasshoppers; that is, we allow no time for the possibility of disease organisms to suppress grasshopper populations. Therefore, the other approach is to treat corn or soybeans according to established thresholds in the respective crops. In corn, treatment for grasshoppers may be warranted if you find seven or more grasshoppers per square yard. After pollen shed, control may be justified when grasshoppers are feeding on leaves above ear level. In soybeans, treatment may be warranted if defoliation reaches or exceeds 40 percent before bloom, or 15 to 20 percent between bloom and pod fill. Also, watch carefully for damage to corn ears and soybean pods. This type of direct damage can result in significant reductions in yield.

We have no idea how large densities of grasshoppers will be this summer. Please contact us if you begin to encounter significant numbers of grasshoppers.--Kevin Steffey

Author: Kevin Steffey