The 2006 grasshopper prediction map for Nebraska indicates that large areas of the state's central and southwest rangeland are at high risk for grasshopper infestations. The USDA-APHIS (Animal and Plant Health Inspection Service) survey (see map) shows areas where adult grasshopper numbers last year would warrant significant concern for developing economically damaging populations this year.
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Some of these same areas were predicted to have high grasshopper numbers last year as well; however, last year grasshopper pressure was much reduced from recent years. Two factors contributed to this situation last year.
First, the cool, wet weather that we experienced across most of the state in late May and early June had a very negative effect on grasshopper survival. Immediately after grasshoppers hatch from their eggs, they are very vulnerable to this cool wet weather because they have very little fat reserves. If they are unable to feed readily during these early stages, high mortality will result. Because grasshoppers hatch over an extended period, only a portion of the grasshopper hatch was wiped out, but this mortality was significant enough to reduce heavy populations in many areas.
Second, the increased growth of range grasses due to increased available moisture contributed to fewer problems last year. The increased grass growth resulted in less conflict over this resource, and the impact of the grasshoppers was minimal, even though their densities were high in some places.
Control options
If serious infestations of grasshoppers develop, control may need to be considered. In recent years, the reduced agent/area treatment (RAATs) program has been widely used and ranchers have been very satisfied with the levels of control they have seen with this program.
The program consists of spraying a swath and leaving a swath untreated so that only half of the treatment block is sprayed, reducing the cost of treatment. This program can be used with any of the three insecticides registered for rangeland grasshopper control, but Dimilin has been used almost exclusively with this program in Nebraska. Advantages with Dimilin lie in its longer residual (21-28 days) that allows time for grasshoppers to move from the untreated areas into the treated area and contact the insecticide. The overall effectiveness of control may be reduced slightly with this program, but the costs will be reduced by 50% or more. In 2004 privately contracted RAATs treatment costs ranged from $1.35 to just over $2.00 per protected acre. Future costs will likely increase because of increased fuel costs. The greatest cost determinant for RAATs treatments is the size of the treatment block -- larger blocks are much more efficient for applicators to treat.
Because of the potential threat of high grasshopper densities this year, ranchers should monitor the buildup of grasshopper densities in these high risk areas beginning at early hatch in late May and into mid to late June. As we saw last year, the damage potential from grasshopper populations will be modified by the environmental conditions we experience. The greatest risk will be if conditions are warm and dry during the grasshopper hatching period.
Gary Hein
Entomologist, Panhandle REC, Scottsbluff
Jack Campbell
Entomologist, West Central REC, North Platte
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