GRANULAR AND LIQUID INSECTICIDE EVALUATIONS FOR LARVAL CORN ROOTWORM CONTROL, 2008

Planting time soil insecticide screening trials were conducted near Clay Center, NE to evaluate their effectiveness for larval corn rootworm control in field corn. Local population consists predominately of WCR (>95% of total). Trial site was lateplanted corn (insecticide free) during 2007. Experimental design was a RCB with 4 replicates. Plot size was 2 rows × 145 ft length (N-S orientation) in 30-inch row spacing. Soil type was a Crete silt loam. ‘Novartis N71M-GT/CB/LL’ hybrid field corn was planted on 01 May 2008 with a 2-row 7100 JD Maximerge planter with finger pickup seed units. A westnorthwest wind @ 12-16 mph occurred at planting. Granular insecticides were applied via standard insecticide boxes in either a 7 inch band over the open seed furrow and in front of the press wheels (TB) or directed into the open seed furrow (IF). A CO2 pressurized sprayer mounted on the planter was used to apply liquid insecticides. Microtubes positioned between the disc openers were used to direct an in-furrow spray solution of 5 gpa water (MTIF) or liquid insecticides were applied in a 7 inch band over the open seed furrow and in front of the press wheels in 5 gpa water (LTB). Plant populations were evaluated on 21 May. The total number of plants per plot was recorded and converted to plants per acre. Corn rootworm egg hatch was first observed on 02 Jun. The total number of lodged plants per plot was recorded on 09 Jul and converted to % root lodging. Larval feeding damage was evaluated on 15 Jul. Five randomly selected plants were dug from each plot, washed, and rated using the Iowa State 0-3 scale (0 = no feeding, 1 = one node of roots pruned to within 1.5 inches of the stalk, 2 = two nodes of roots pruned to within 1.5 inches of the stalk, 3 = 3 or more nodes of roots pruned to within 1.5 inches of the stalk). The total number of lodged plants per plot was also recorded on 25 Sept and converted to % root lodging. Plots were machine harvested on 02 Nov. Percent moisture and lbs of grain were recorded and corrected to 56 lbs/bu @ 15% moisture. Data were analyzed by ANOVA with mean separation using differences of least square means (P = 0.05).