Abstract Rootworm planting time, soil insecticide test plots were established at 6 Iowa locations. Two of these locations were also used for cultivation-time tests. The insecticide histories of the test fields were: Nashua and Sutherland—trap crop (no insecticide)/insecticide test plot, yearly alternation for at least the past 5 years; Ames—Lance '83, '84, '85, no insecticide '82; Clarence—Counter '82, Amaze '83, insecticide test plot '84, no insecticide '85; Kellogg—Furadan '82, Counter '83, '84, '85; Newell—no insecticide '82, '83, '85, insecticide test plot '84. The experimental design was a randomized complete block with 4 replications for the root-protection trials and 8 replications for the Nashua, Newell and Sutherland yield trials. All treatments were applied to 50 ft length rows with 30 inch row spacing. The yield trials had double-row treatments. All other trials had single-row treatments. Granular insecticide formulations were applied with modified Nobel® metering units that had been laboratory-calibrated to accurately deliver material at a tractor speed of 4 mph. The applicators were mounted on a 4-row John Deere® Max-Emerge™ 7100 integral planter equipped with ripple coulters. Drag chains were used for incorporation. Liquid insecticide formulations were applied immediately after planting with a small-plot sprayer mounted on a bicycle-wheel applicator and pressurized with a CO2 canister. Liquids were applied in a 7 inch band over the row. Dyfonate 4EC, Dyfonate 4.6S, Furadan 4F and Lorsban 4E were applied with a Tee Jet® 8003E nozzle at 20 psi to deliver 10 gpa. Broot 50W and Lorsban 50W used a 8008E nozzle at 14 psi to deliver 20 gpa. A rake dragged lightly over the soil surface was used for incorporation. Cultivation-time insecticide applications were made with electrically driven Noble units mounted on the tool bar of a 2-row, rear mounted cultivator. Plastic tubes directed the insecticide to both sides of the corn row directly in front of the cultivator sweeps (basal treatment). A bander positioned directly over the plant whorl was used for the whorl treatment. Liquid insecticides were applied just prior to cultivation with the small-plot bicycle sprayer. In late Jul rootworm feeding was evaluated by digging 5 roots from each treatment row and rating the damage on the Iowa 1-6 scale (1 equal to no feeding, and 6 equal to 3 nodes of roots completely destroyed). Chemical phytotoxicity was checked by taking stand counts and plant height measurements for each treatment. Lodging counts were taken in late Jul at Clarence and at harvest time at Nashua. The Nashua yield trial was machine harvested. Data were analyzed using analysis of variance procedures.