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Issue No. 17, Article 2/July 17, 2009

Insect Observations from the North-Central Region

On July 13, extension entomologists exchanged observations by teleconference about insect pests of field crops in their respective states. Provided here are summaries for the key insects we discussed.

Soybean aphids. In general, soybean aphid densities are low in many north-central states, including Illinois. In Ohio, overall densities remain low; however, some fields are showing signs of infestations further to the south than in recent years. Low numbers of soybean aphids also were reported in Indiana, Nebraska, and South Dakota. In Iowa, expectations are that in some fields, the economic threshold may be reached in the next 7 to 10 days. Producers are encouraged to familiarize themselves with scouting procedures and to be ready to make a management decision if average densities reach 250 aphids per plant in soybean fields.

Further to the north, the economic threshold has been reached in certain fields in eastern Ontario. In Illinois, overall reports of aphids remain very low and widely scattered. Ryan Stoffregen, Advanced Crop Care, reported that two soybean fields in McHenry County near Marengo have had very low levels of aphids (1 to 10 aphids per plant) for the past 3 weeks. One field had 30% to 40% of the plants infested; the infestation in the other field ranged from 10% to 30%. Ryan also reported that soybean aphids have been found in the last week in DeKalb and Boone counties; fewer than 10% of plants were infested, with typical densities of two aphids or fewer per leaf. So, as previously reported, soybean aphids are off to a slow start this season across a large area of the Corn Belt. But we have a long way to go this summer with this insect pest, and soybean fields should be scouted regularly to optimize any management decisions that may be required.

Corn rootworms. Very few reports were offered with respect to corn rootworms; however, western corn rootworm adult emergence is well under way in Illinois. Entomologists at Purdue University have observed very low levels of root injury in their experimental plots. We intend to begin our root evaluations early next week and look forward to sharing the results of our annual root "digs" in upcoming issues of the Bulletin. The low levels of root injury reported by Purdue entomologists may be the result of the very wet soil conditions at the time of larval hatch this spring.

Western bean cutworms. Entomologists in Ohio reported that larger numbers of western bean cutworms have been observed this season than in previous years. Entomologists at Purdue reported increases in captures have occurred during the past week and in some corn fields (northwestern Indiana) egg masses and emerging larvae can be found. Illinois producers are encouraged to begin scouting corn fields for western bean cutworms. If 8% of plants have an egg mass or young larvae, consider a rescue treatment. For more complete life cycle and management recommendations, visit ipm.illinois.edu/fieldcrops/insects/western_bean_cutworm. If you are experiencing significant infestations of western bean cutworm in your area of Illinois, please let me know and I will share your observations with readers.

Japanese beetles. Reports of Japanese beetle infestations continue, particularly in the eastern Corn Belt. For the next several weeks, producers are encouraged to monitor their corn fields for silk clipping and soybeans for defoliation. Because these beetles tend to concentrate in border rows of both crops, rescue treatments applied to field margins may be sufficient in some cases.--Mike Gray

Author:
Mike Gray

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