Should You Treat for Grasshoppers?
Recently, a Southcentral-Illinois integrated pest management specialist reported large numbers of grasshopper nymphs feeding in weedy areas. After they finished with the weeds, he reported, they started in on crops nearby and took quite a toll.
Though this situation was seen in Illinois, it could very well be developing in Indiana, according to Purdue entomologists Rich Edwards, John Obermeyer and Larry Bledsoe.
After nymphs hatch, they normally feed near their eggs for two to three weeks. When that food source runs low or when their early feeding sites are mowed or otherwise destroyed, the entomologists say the nymphs move to other feeding sites, including nearby crops.
The best time to manage threatening grasshopper populations is when they are still in the nymphal stage because they are less mobile and more susceptible to insecticide. However, the three specialists caution that a control should not be applied just because you see nymphs. First, determine if the population is economically significant.
To do that, pinpoint infestations in crop and non-crop areas. In at least five random locations within each infested area, estimate the number of grasshoppers within approximately one square yard. Then determine the infestation level for each sample area, and for each crop and non-crop area as a whole.
Treatment of field margins is probably justified if counts exceed 15 or more nymphs per square yard.
In soybean fields, the entomologists say control may be needed if defoliation levels exceed 40 percent prior to bloom or 15 percent from blooming to pod-fill.
In corn, They say it may be advisable to treat if an average of three or more grasshopper nymphs per square yard are present. In many cases, spot treatment may be sufficient to control the grasshoppers. If you have questions about controlling grasshoppers, contact your local Extension office for further help.