Rangeland Grasshopper Management Update - UNL CropWatch May 13, 2011

Rangeland Grasshopper Management Update - UNL CropWatch May 13, 2011

May 13, 2011

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USDA has indicated that areas of Nebraska pasture and rangeland are at high risk of damaging grasshoppers this year, based on the number of grasshopper eggs at the start of last winter (see January 2010 CW).

However, a cool, wet May along with beneficial organisms can reduce grasshopper numbers (see May 2010 CW). So far, many areas of western Nebraska have remained cool and wet, while some areas have remained relatively dry. As is often the case, some areas of Nebraska will be much more affected by grasshoppers than others.

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 wire template 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.

The Nebraska Panhandle and much of southern Nebraska should begin seeing the first grasshopper hatch of the season this week (Figure 1). These are not the bandwing grasshoppers that overwinter as late nymphs or adults and would have appeared in March or April. These grasshoppers spent the winter as eggs in the ground and have now begun to hatch.

To estimate the potential for damaging populations of grasshoppers on rangeland, use the following method.

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 ft2 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 1 ft2 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 1 ft2 (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 1 ft2 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 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.

Nebraska Grasshopper Management Programs

Three meetings will be held in north central and western Nebraska in late May to provide an update on the state's grasshopper situation. Meeting topics will include:

  • Summer 2011 — A Climate Outlook, with Mathew Masek, general forecaster for the National Weather Service
  • Balancing Forage Supply and Demand — Including Grasshoppers with Jerry Volesky, extension range and forage specialist, West Central REC, North Platte
  • Grasshopper Biology, Control Strategies and Survey Updates with Dave Boxler, Extension Educator - Entomology, West Central REC, North Platte

The meetings will be held at 1:30 CDT at the following locations:

  • May 25, Broken Bow, Custer County 4-H Building
  • May 26, Thedford, THomas County Courthouse
  • May 27, North Platte, West Central REC

For more information on any of these meetings, contact Dave Boxler at dboxler@unlnotes.unl.edu or phone: 308-696-6721.

Visit the Department of Entomololgy grasshopper website for more information on grasshoppers, grasshopper management, and a list of compounds that can be used to control grasshoppers in Nebraska.

Jeff Bradshaw, Extension Entomologist
Panhandle REC, Scottsbluff
David Boxler, Extension Educator
West Central REC, North Platte
Bob Wright, Extension Entomologist, Lincoln