Grasshopper populations are abundant in some soybean fields this summer.
Red-legged grasshoppers are common in soybeans.
Reports indicate that half-inch grasshoppers are abundant in many ditches, fencerows and waterways. Paul Kassel, extension field specialist in crops at Spencer, reports that border rows in some soybean fields are heavily defoliated. Only nymphs have been found so far.
Grasshopper nymphs defoliating soybean leaves.
There are no good economic thresholds to use in either corn or soybeans. Old thresholds recommended counting the number of grasshoppers per square yard, but I do not like this method. Counting grasshoppers in either corn or soybeans is a near impossibility because they are either partially hidden in the foliage or they constantly hop out of the area you’re trying to count. I would suggest the use of a nominal threshold (one based on experience), combined with a measurement of leaf defoliation, and a little common sense in managing grasshoppers. It is usually not too difficult to determine if grasshoppers are abundant so forget trying to count the number per square yard.
In soybeans, consider treatment if grasshoppers are present and defoliation reaches 40 percent in the vegetative stages, or 20 percent in the pod-forming and filling stages. Determine the exact location of grasshoppers in the field and spray only those areas. Grasshoppers are often concentrated along field edges, but they sometimes occur in large areas out in the center of the field, especially if weeds were present last year. Reductions in yield can occur during any crop stage; pod-forming/pod-filling stages are at greater risk than other plant stages. A 40 percent leaf loss during any vegetative stage will result in only a 3 to 7 percent yield reduction. Defoliation of 20 percent during the pod-forming and filling stages will result in similar yield reductions.
Grasshopper injury in corn last summer (1995).
In corn, consider treatment if grasshoppers are present and they are clipping silks, ear tips, or removing large amounts of foliage above the ear leaf. Grasshopper problems I’ve seen in corn usually begin on border rows and then move deeper into the field. Determine how many rows are infested and spray only those rows.
In all crops, remember that grasshopper nymphs will eventually become adults and cause more leaf loss during August and September, but they should not be sprayed until the injury approaches a level that could cause economic yield loss. This may not occur until the nymphs become adults. Fortunately, some of the insecticides provide excellent control of adult grasshoppers. Another consideration before spraying is that a naturally occurring fungus can reduce hopper populations and economic damage may never occur in the field.
Recommended insecticides for
grasshopper control in corn and soybean.
||Rate per acre
|Asana XL 0.66EC*
|Sevin XLR Plus
||2.56-3.84 oz. (corn)
||3.20-3.84 oz. (soybeans)
This article originally appeared on pages 123-124 of the IC-476(18) -- July 15, 1996 issue.