Western Nebraska grasshopper update
The year’s second hatch of rangeland grasshoppers is now under way in western and Central Nebraska, and locally heavy infestations are being experienced in Box Butte, Lincoln, Morrill, and Scotts Bluff counties.
However, other areas may also be experiencing large outbreaks as this hatch continues. We recommend that landowners scout their property now to determine if they have an economically important grasshopper infestation.
Treatment is warranted when grasshopper nymphs are spotted that are at the 3rd and 4th instar and number on average between 25 and 30 per square yard. Grasshoppers develop through four immature stages, or instars, prior to becoming winged adults.
The western half of Nebraska was determined to be at a high risk for rangeland grasshopper infestations this spring and early summer, based on the 2009 fall grasshopper survey conducted by the U.S. Department of Agriculture.
Western Nebraska generally experiences three population peaks of grasshoppers early in the year. The earliest grasshoppers can sometimes be seen even on warm days in February. They overwinter as adults or well-developed immature grasshoppers, and often do not cause problems. However, the remaining two populations overwinter in the egg stage in protective cases in the soil. The grasshoppers that hatch from these eggs result in most of the grasshoppers seen right now.
The first hatch began about one month ago and resulted in fewer grasshoppers than expected. The unusually cool and wet weather this spring killed many of the grasshoppers.
For pasture or rangelands the recommended treatment is to use is the RAAT’s system (Reduced Area and Agent Treatment). With this approach treated swaths ranging from 100 feet to 150 feet in width are alternated with 100-foot to 150-foot-wide untreated swaths. This treatment strategy reduces the amount of insecticide applied to treated areas by 50 percent.
The insecticide that is used with this system is Dimilin® 2L, which has residual activity approaching 28 days. The recommended rate of application is 1 ounce of Dimilin plus 3 ounces of canola oil plus 1 ounce of concentrated crop oil per acre. The crop oil acts as a dispersant, and the canola oil acts as a bait to attract the grasshoppers into the treated swaths.
The most important factor using this treatment strategy is to apply this control product when 4th instar grasshopper nymphs appear. This product will not work on adult grasshoppers. Treatment at the appearance of 4th-instar grasshoppers ensure that a most of the grasshopper population has hatched and all are susceptible to the insecticide.
A survey of ten Nebraska aerial applicators in May indicated that the cost of this type of treatment ranged from $3.00-$9.84 per treated acre or $1.50-$4.93 per protected acre. A treated acre is the area where the insecticide was actually applied. A protected acre includes the treated acre along with the untreated acre.
Growers should note that if they had significant problems with grasshoppers damaging crops last year, there is a chance that that problem will occur this year in the same areas. Now is the time to look at crop borders and ditch banks for small grasshoppers, especially in fields adjacent to pastures. To reduce the chances of experiencing grasshopper damage to crops this year, now is the time to make an application to the crop borders of your fields. For field crops for which Dimilin® 2L is labeled, we recommend using a 2 ounce rate along with 1 ounce of concentrated crop oil per acre. Be aware that Dimilin® 2L is not labeled for corn or alfalfa, but it is labeled for crops such as soybean and wheat. For more information on grasshopper identification, scouting procedures, and additional control options please consult entomology.unl.edu/grasshoppers.
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