Impact of Planting Dates of Field Corn on Beetle Emergence and Damage by the Western and the Northern Corn Rootworms1 in the Corn Belt2

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Abstract
A 2-yr study was initiated in 1975 in the North Central States of Illinois, Indiana, Minnesota, Nebraska and Ohio to evaluate the effect of planting date of field corn (Zea mays L.) on beetle emergence and damage by the western, Diabrotica virgifera LeConte, (WCR) and northern, D. longicornis (Say), (NCR) corn rootworms. It was observed consistently that adult emergence for both the NCR and WCR peaked relatively rapidly and declined at an equally rapid rate from corn planted in late Apr. or early May. Emergence from corn planted in late May peaked later in the season, occurred over a longer time period, and declined at a slower rate than for the earlier plantings. All of these trends were even more evident for early and mid-June plantings. Peak emergence averaged ca. 3 wk later for the late May and early June plantings and averaged 5.5 wk later for mid-June plantings than for the late Apr. and early May plantings. Initial and peak beetle emergence of the NCR were 1 and 2 wk later, respectively over those for WCR. The highly significant relationships (P < 0.01) between planting date and root damage was strongly linear for all states. These data indicate that for each 10 day delay in corn planting after Apr. 1, the average root damage rating would decrease 0.48, 0.71, 0.77, 1.05, and 1.08 units for Ohio, Minnesota, Missouri, Illinois, Indiana and Nebraska, respectively.

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