Predicting western corn rootworm (Coleoptera : Chrysomelidae) larval injury to rotated corn with pherocon AM traps in soybeans

Crop rotation for portions of east central Illinois and northern Indiana no longer adequately protects corn (Zea mays L.) roots from western corn root worm, Diabrotica virgifera virgifera LeConte. Seventeen growers in east cen tral Illinois monitored western corn rootworm adults in soybean (Glycine ma x L.) fields with unbaited Pherocon AM traps during 1996 and 1997. In the f ollowing years (1997 and 1998), growers left untreated strips (no insectici de applied) when these fields were planted with corn. Damage to rotated cor n by rootworms was more severe in untreated than in treated strips of rotat ed corn, ranging from minor root scarring to a full node of roots pruned. D ensities of western corn rootworms in soybean fields from 1996 were signifi cantly correlated with root injury to rotated corn the following season. Ad ult densities from 1997 were not significantly correlated with root injury in 1998, due to heavy precipitation throughout the spring of 1998 and exten sive larval mortality. Twenty-eight additional growers volunteered in 1998 to monitor rootworm adults in soybean fields with Pherocon AM traps based o n recommendations that resulted from our research efforts in 1996 and 1997. In 1999, these 28 fields were rotated to corn, and rootworm larval injury was measured in untreated strips. Based on 1996-1997 and 1998-1999 data, a regression analysis revealed that 27% of the variation in root injury to ro tated corn could be explained by adult density in soybeans the previous sea son. We propose a sampling plan for soybean fields and a threshold for pred icting western corn rootworm larval injury to rotated corn.