While Colorado bug watchers are seeing some grasshopper nymphs in the northeastern state, populations remain much smaller than economic threshold for the pest, reports Colorado State University Extension Specialist Assefa Gebre-Amlak.
U.S. Department of Agriculture Animal and Plant Health Inspection Service counts in mid-June show lower numbers (1-8 nymphs) per square yard in most of the area, except two sites south of Wray in Yuma County, where 9-14 were found.
The nymphs were at the first and second instar stages, says Gebre-Amlak, noting that there appears to be delayed hatching and emergence of grasshoppers in most of the area.
Landowners in high risk areas should continue monitoring populations,Gebre-Amlak advises, particularly in rangeland regions. Early scouting is important since treatments are most effective when grasshoppers are small. The goal of scouting the crops is to get an estimate of pests per square yard, as well as their stage of development.
High risk of crop-devastating infestations is predicted for Yuma, Logan, Morgan and Washington counties in northeastern Colorado. Other counties with more localized spots of high risk include Kit Carson, Weld, Phillips. Sedgwick, Lincoln, Cheyenne, Kiowa, Powers, Bent and Otero.
Weather conditions will determine how much of the outbreak potential will be realized.
For example, cool, wet conditions after hatch can result in enough pest mortality in immature grasshoppers to prevent an outbreak. If adequate moisture is available, forage regrowth will offset much of the hopper damage.
Most grasshopper infestations occur when drought conditions prevail.
Economic threshold for grasshoppers on rangeland is 15-20 nymphs per square yard. This number should result in 8-10 adult grasshoppers per yard.
There are more than 100 species of grasshoppers in Colorado, but only about a dozen present a real menace to rangeland, says Gebre-Amlak. Five species are found the cause the most damage to crops, and growers should be able to identify species as they scout for the pests.
For details, go to the grasshopper management website at www.nocopestalert.org.