| Grasshopper alert for eastern Oregon: major outbreak possible in 2008 |
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This year has seen a large buildup of grasshoppers in Eastern Oregon. At the beginning of June, 2007 high numbers of grasshoppers were reported in the Haines area. Surveys recorded economic infestations of grasshoppers stretching from Elgin in Union County to Baker City in Baker County (see attached map). Economic levels are 8 grasshoppers per square yard and above. As of September 2007, almost 600,000 acres are infested with up to 50 grasshoppers per square yard!
The last major grasshopper outbreak in Baker County was in 1986. Records of historical outbreaks date back to 1954 when more than 15,000 acres south of Halfway were heavily infested with grasshoppers. In that same year, over 4,000 acres were infested northeast of Enterprise in Wallowa County. Grasshopper outbreaks on range and cropland in Wallowa, Union and Baker counties were treated with aerial applications of Malathion in 1969, 1972, 1974, 1979, 1980, 1985 and 1986 totaling more than 632,000 acres (map).
The predominant grasshopper species recorded in 2007 was the clearwinged grasshopper, Camnula pellucida. This grasshopper can be an important pest of small grains (barley and wheat), and grasses, such as wheat grasses, fescues, bluegrasses, and bromes. The most destructive period is in the spring when Camnula can destroy entire spring wheat fields. Swarms of adult grasshoppers may later invade vegetable crops including onions, lettuce, peas, etc. Adult Camnula can migrate long distances in huge flying swarms from their feeding grounds to egg laying areas. Each female deposits up to 200 eggs in the soil. In early spring, myriads of the clearwinged grasshopper nymphs hatch in egg beds that may contain as many as 3,000 to 100,000 eggs per square foot. High grasshopper densities and lack of food force the immature grasshoppers to move away from the egg beds to the nearest green vegetation.
Camnula populations can be low for periods of up to ten years, then increase gradually over three to four years and reach peaks the following two to three years. During the period of increase, a population may spread from a few acres of rangeland to more than 2,000 square miles. The factors favoring outbreaks appear to be a combination of favorable weather, nutritious host plants, and reduced rates of predation, parasitism, and disease.
A warm and dry spring in 2008 would favor an increase in the grasshopper populations in Eastern Oregon. Considering that the immature grasshoppers (nymphs) cause the most damage, early spring surveys of the egg beds are essential in the effort to control grasshopper populations. Control options include flood irrigation of rangeland (where possible) and chemical control. Insect growth inhibitor regulators (IGR), such as Dimilin, have a high success rate for controlling immature grasshopper populations while significantly reducing the risk to other non-target species, such as honeybees and native pollinators, and applicators. However, application timing of these products is critical since only molting insects are affected. Once the grasshoppers become adults, IGR’s are no longer effective. Also it is very important that all ranchers and growers affected by grasshoppers in an area work together on a control program to avoid re-infestation from non-treated areas. This happened to one rancher in Haines who successfully treated against grasshopper nymphs in early spring just to have his fields overrun again by adult grasshoppers flying in from neighboring non-treated fields later in the summer.
Last year’s positive experiences in the Fort Klamath area (Klamath County) clearly show that a combined effort can successfully control an outbreak of the clearwinged grasshopper over a large area. More than 20,000 acres were protected with aerial applications of Dimilin. Using the RAATs (Reduced Area and Agent Treatment) system, spraying one swath and leaving one swath untreated, application costs came to about $2.00 an acre.
Although no one can accurately predict weather conditions that may or may not favor a huge grasshopper outbreak in the spring, prevention and control options should be discussed and preparations made by stakeholders now in order to avoid a potentially disastrous grasshopper infestation in 2008.
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