Continued Good News for Grasshopper Risk On Rangeland - UNL CropWatch, June 6, 2013

Continued Good News for Grasshopper Risk On Rangeland - UNL CropWatch, June 6, 2013

 Map showing risk areas for rangeland grasshopper risk

Figure 1. Results of 2013 rangeland grasshopper and Mormon cricket nymphal survey, as reported by USDA APHIS May 31, 2013. (Links to larger version.) (Source: USDA APHIS)

June 6, 2013

Diagram of grasshoper sample pattern

Figure 2. Example sampling pattern for rangeland grasshopper scouting.

Photo: One square foot wire shape used to sample for grasshoppers

Figure 3. A one-square-foot wire template can be used to help envision the sample area used for estimating grasshopper density.

Photo: Differential grasshopper

Figure 4. A 3rd instar differential grasshopper nymph. A species that is more typically a concern in late summer on crops.

This year the Panhandle is the area in Nebraska at greatest risk for damaging grasshopper feeding in rangeland, according to USDA Animal and Plant Health Inspection Service (APHIS) scouting reports. Overall surveys have revealed some of the lowest grasshopper densities statewide in years (Figure 1).

USDA APHIS provides regular updates on the status of rangeland grasshoppers across Nebraska. As noted previously, grasshoppers pose the least of many concerns for rangeland in 2013.

Currently 3rd instar grasshoppers are beginning to appear in southwest Nebraska and some 4th instars are appearing in the Sandhills. The Panhandle grasshopper populations are just beginning to emerge with most being 1st instars.

Although numbers are low, some locations will benefit from scouting.

How to Estimate Grasshopper Density

The following method is based on information in the USDA Agricultural Research Service resource, Grasshoppers: Their Biology, Identification and Management, by James S. Berry et al.

The 18-square-foot sample method used by many APHIS offices in the western United States is a simple and quick way of determining the density of grasshoppers on rangeland. At each survey site, choose a sample area typical of the rangeland to be surveyed. Next, look ahead and determine the approximate route you will walk (Figure 2). Pick a spot on the ground about 10 paces in front of you. Choose the spot before you determine if any grasshoppers are present.

Visualize a sample area surrounding the spot equal to one square foot on the ground. You can use landmarks such as a stick, pebble, tuft of grass, or flower to help keep your eye focused on the sample area chosen. Or you can use a piece of wire bent into a one square foot (Figure 3) placed at your feet to help train your eye. Once the area is set, walk slowly toward it and determine the number of grasshoppers by counting the grasshoppers as they flush out of the visualized sample area.

Do not count individuals that hop into the sample area while conducting the sample count. When you reach the spot, probe the area with the handle of your insect net or other suitable object to make sure all individuals have flushed and been counted. Record the number counted and repeat the process at 17 more sample areas. The total number of grasshoppers counted in the 18 one-square-foot sample areas, divided by 2, gives you the number of grasshoppers per square yard.

Grasshoppers develop through four immature stages, or instars, prior to becoming winged adults. For optimal treatment, delay treatment until you begin to spot 3rd and 4th instars (Figure 4). (For help with staging grasshoppers, see the UNL Department of Entomology Grasshopper website.) Treatment is warranted when grasshopper nymphs at the 3rd and 4th instar are spotted and the total number averages 25 to 30 per square yard.

Note that some areas of Nebraska may have restrictions on pesticide applications due to deleterious impacts to state or federally protected species. (Please refer to Nebraska information and distribution maps on the U.S. Fish & Wildlife Service website for details.) However, producers and landowners can request a site specific survey to be conducted by APHIS. Contact your local Extension Office or call USDA-APHIS directly at 402-434-2345.

Jeff Bradshaw
Extension Entomologist, Panhandle REC