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Western Corn Rootworm Damage: Effect of Tillage on Plant Response and Grain Yield

USDA, ARS, NPA, Northern Grain Insects Res. Lab., Brookings, SD 57006
Plant Science Dep, South Dakota State Univ., Brookings, SD 57007

^* Corresponding author.

Corn rootworms (Diabrotica spp.) are the most economically destructive insect pests of corn (Zea mays L.) in the U.S. Midwest. The objective of this 2-yr field study was to measure plant response and yield under ridge tillage or spring disk tillage in fields artificially infested with western corn rootworm (D. virgifera virgifera LeConte). Corn rootworm infestations were applied at 0, 1650, 3300, or 6600 viable eggs m^–1. We measured insect survival to adult, root damage ratings, nodal root volume (Nodes 4 and above) at maximum insect damage, and grain yield. In 1988, which was characterized by above-normal temperature and below-normal precipitation, root damage increased (6.7 rating at 1650 eggs m^–1 to 7.9 at 6600 eggs m^–1) and insect survival to adult decreased (4.9% at 1650 eggs m^–1 to 1.2% at 6600 eggs m^–1) with increasing infestation level under both tillage systems. During the 1988 season, plants grown under ridge tillage had larger nodal root systems (17.9 mL) than under spring disk tillage (9.9 mL). Ridge-tilled plants also had greater yield (5.5 vs. 4.1 Mg ha^–1 with no rootworm eggs; 4.3 vs. 3.1 with 1650 eggs m^–1; and 4.1 vs. 2.2 Mg ha^–1 with 3300 eggs m^–1). In 1989, which had near normal temperature but below-normal precipitation during the growing season, root damage increased (from a 1.1 to 5.9 rating as the infestation level increased from 0 to 6600 eggs m^–1) and insect survival to adult decreased (from 1.3 to 0.7% as the infestation level increased from 1650 to 6600 eggs m^–1) under both tillage systems. Tillage practice had no effect on plant response to rootworm feeding or yield. However, the number of nodal root axes per plant (22.4) and grain yield (8.8 Mg ha^–1) were increased significantly under both tillage systems infested with 6600 eggs m^–1 of row (29.0 axes per plant and 10.2 Mg ha^–1). These results suggest that during a hot, dry growing season, ridge tillage increased yield for uninfested and rootworm-infested plants when compared with yields produced using spring disk tillage.

Received for publication July 30, 1990.