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Issue No. 12, Article 3/June 16, 2006

Corn Rootworm Injury Becoming Noticeable

The numbers of reports from people who are finding corn rootworm larvae and observing root-feeding injury have increased over the past week. In some areas where soil moisture is short, corn rootworm larval injury is adding insult to injury. Joe Spencer, research entomologist at the Illinois Natural History Survey, found plenty of second- and third-instar rootworms feeding on unprotected corn in his plots on June 12 and 13. The soil in his plots is dry, and the injured plants have rolled leaves during the day. Injury to the roots is becoming noticeable, with tunneling and some pruning occurring. On a positive note, the YieldGard Rootworm hybrid in his study has not been injured by rootworm larvae and is not showing signs of moisture stress. Clayton Mai, seed specialist/APS, has found rootworm larvae tunneling in roots of V10-stage corn planted after soybean in northern Greene County.

Rootworm larvae feeding on corn plant in Champaign County. The size reference is a dollar coin. (Photo courtesy of Joe Spencer, Illinois Natural History Survey).

With predicted high temperatures and a continued lack of rainfall in some areas, the incidents of rootworm injury will increase. We encourage people to begin checking cornfields now for rootworm larvae and their injury. Although the full extent of rootworm injury in any given field will not be realized for a month or more in many areas, some investigation now might provide an early assessment of the impact of rootworm larvae on corn production. You might also get a head start comparing rootworm injury in untreated areas with rootworm injury in protected corn (i.e., protected with a soil insecticide, seed-applied insecticide, or transgenic Bt protein). In a future issue of the Bulletin, we’ll provide more detail about rating roots for rootworm injury using a scale that quantifies the amount of injury to a root system.--Kevin Steffey

Kevin Steffey

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