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The presentation was part of Oregon State University Extension’s recent annual training for private pesticide applicator certification.
Rogg is the Oregon Department of Agriculture’s local expert on insects. Besides last summer’s outbreak in Union and Baker counties, Rogg has also studied severe grasshopper infestations in Malheur and Klamath counties.
Last summer, the grasshopper population in both Union and Baker counties caused considerable alarm as it spread across more than 270,000 acres. In the worst cases, as many as 75 grasshoppers per square yard were counted, Rogg said, nearly six times what would be considered normal during a seasonal outbreak.
Rogg had hoped there would be some state and federal cost-share money available in 2008 to help local people with pest management. Now, he is encouraging people in the region to work together to solve the problem instead of counting on government help.
“Oregon baled out of the grasshopper program, so that leaves federal money that might pay one-third the cost — if you get approved,” he told the nearly 30 men and women at Monday’s session.
“But if you do it yourselves, you will be working as private applicators and the cost will be significantly less,” Rogg said. “But you need to get organized. Get everyone in the area to spray, or it is useless.”
NORTHEAST OREGON INFESTATION: The darker red areas show grasshopper populations that have been documented for years in central Wallowa County and northeast of Baker City. The green indicates the enlarged areas where grasshopper populations were documented just last year. - Observer photos/MARDI FORD
In early May a survey will be conducted to see what grasshopper numbers look like. Then between mid-May and the June 1, the preferred pesticide will have to be applied in order to be effective.
Of the three chemicals federally approved to battle grasshoppers — Malathion, Carbaryl and Dimilin — Rogg prefers the Dimilin (diflubenzuron) for three basic reasons: cost, safety and effectiveness.
“If you do it yourselves, you can apply Dimilin for $2 to $4 an acre and, unlike Malathion, it is very species specific,” he said.
Dimilin is applied at a ratio of approximately one ounce per acre and works by ingestion, not by exposure. That makes Dimilin safer for applicators and even safe to use around honey bees.
“It won’t harm our pollinators,” Rogg added. “But we can’t spray it around water.”
Dimilin has been shown to be toxic to some species of aquatic invertebrates like shrimp, he explained.
Dimilin can be applied in 100-foot swaths with 100 feet in between, saving the additional cost incurred with a blanket spray. The chemical used in Dimilin is mixed with canola oil and water. Grasshoppers are attracted to the smell of the canola oil and seek it out wherever it is coating vegetation.
Dimilin works as a growth inhibitor during the early stages of the maturation cycle. It interferes with the development of the exoskeleton. Grasshoppers that eat Dimilin will die while trying to molt, since the new outer layer is not properly formed. The nymph dies in its old skin before it matures.
GRASSHOPPER PEST MANAGEMENT 101: Entomologist Helmuth Rogg presented the current situation coming out of the 2007 grasshopper infestation as part of Oregon State University Extensionâ€™s annual training for private pesticide applicator certification for Union, Wallowa and Baker counties. His advice? Organize and be proactive with treatment. - Observer photos/MARDI FORD
It is the vulnerable nymphs that are the voracious eaters causing the greatest damage to forage and crops. They must consume huge amounts of food to grow into mature grasshoppers, ready to mate and fly. So although Dimilin does have a two-week residual affect, it must be applied during a specific window.
“There is about a four-week critical stage when the Dimilin must be applied.
Rogg says pesticide control makes more sense during the nymph stage anyway. Once grasshoppers reach the adult stage, the crop damage is already done. Grasshoppers have matured, mated, laid their eggs for next year’s hatch and are already dying.
Although rangeland in the Grande Ronde Valley is more limited and crops on the valley floor escaped severe infestation last summer, in an extreme outbreak with limited food sources, Rogg said grasshoppers will happily eat wheat.