Biological Control of the Western Corn Rootworm Using Steinernematid Nematodes, 1993

Efficacy of Steinernema riobravis and Steinernema carpocapsae, All strain, as biological control agents for WCR was evaluated on a Waukegan silt loam soil at the University of Minnesota Agricultural Experiment Station, Rosemount. Experimental plots, consisting of 36 plants in 3 rows of 12 (30-inch row spacing, planted 14 May) were infested on 11 Jun with 700 WCR eggs/row-ft. Most plants had reached the 2-leaf stage when infested. The experiment used a randomized complete block design, with 4 rates of S. carpocapsae (104, 105, 10", and 107 nematodes/row-ft), 4 rates of S. riobravis (103, 104, 10\ and 10" nematodes/row-ft) and an agar control, replicated 5 times. Nematodes (BioVector®) were applied when the rootworm population had reached its early 3rd instar (19 Jul). Twelve ml of 0.15% agar nematode suspension were applied around the base of each treated plant with a 35 ml syringe. Despite an extremely wet summer, dry weather in the week preceding nematode application resulted in insufficient near-surface soil moisture for nematode movement. The plots were watered before application until evenly moist to a depth of 10 cm. On 29 Jul, 4 emergence cages, each covering 2 plants, were installed per plot. Beetles were collected every 10 days until 1 Oct. Ten roots per plot were dug, washed, and rated using the Iowa 1-6 root injury scale on 14 Sep.