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Grasshopper infestations spotty across the state, some may warrant treatmentNebraska High numbers of grasshoppers are showing up in some parts of the state, University of Nebraska-Lincoln entomologists say. While infestations are spotty and vary across the state, now is the time to check for grasshoppers before the majority become adults. "The best time to control grasshoppers is when they are concentrated in field border areas before they spread into the crops and before they become adults and become harder to control," said Gary Hein, UNL entomologist at the Panhandle Research and Extension Center at Scottsbluff. In many areas, numbers of smaller grasshoppers are unusually high for this late in the season. "This likely is due to poor survival of the early hatching grasshoppers caused by the earlier cool, wet weather," said Bob Wright, fields crop specialist in the university's Institute of Agriculture and Natural Resources. During grasshoppers' early stages after hatching, they have a very high mortality rate if conditions are cool and wet. However, in some situations, grasshoppers already have moved into and have begun to damage crops, Hein said. Since grasshoppers do not like to enter dense plant canopies, damage is most often limited to field edges, Hein said. Border treatments often are used to protect cropland from grasshoppers. "Because grasshoppers move into cropland from untilled field borders with mixed grass and broadleaf weeds, grasshopper surveys should be conducted in these adjacent untilled areas," Hein said. "Growers need to watch closely. If they don't, they could get into a crisis situation." To estimate grasshopper densities that warrant control, count the number of grasshoppers by using a square-foot method Wright said. Randomly select an area and visualize a square-foot area. Walk toward that spot and count the number of grasshoppers seen in or jumping out of this area. Repeat this procedure 18 times and divide the total number of grasshoppers by two. This will give the number of grasshoppers per square yard. Counting sites should be done at random and vary in vegetation. To sample for grasshoppers within fields where grasshopper density will be lower, use the same method except visualize and count the grasshoppers in a square yard. An economic return on treatment is likely when infestations are moderate--eight to 14 grasshoppers per square yard within fields and 20 to 40 grasshoppers per square yard in field borders. Due to increased crop value of many crops, a light infestation of three to seven grasshoppers per square yard in fields and 11 to 20 in field borders also may warrant treatment, depending on the size, species and crop. Insecticides are labeled and effective for grasshopper control on various crops. For more information about spraying for grasshoppers, including a list of insecticides and several publications, visit the UNL Department of Entomology website at http://entomology.unl.edu/grasshoppers/. 8/18/08 Date: 8/12/08
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