Western Corn Rootworm Damage Subtly Affects Corn Growth under Moderate Environmental Stress

Abstract

Western corn rootworm (Diabrotica virgifera virgifera Le Conte) is more prevalent because of its increased adaptation to crop rotation and increased continuous corn (Zea mays L.). A 2‐yr field study using seed and soil‐applied insecticide treatments evaluated growth responses of corn to rootworm damage. The control had moderately severe (1.40 on a 0–3 node‐injury scale), whereas the 1.25 mg kernel−1 clothianidin [(E)1‐(2‐chloro‐1, 3‐thiazol‐5‐ymethyl)‐3‐methyl‐2 nitroguanidine] treatment had minor (0.18) rootworm damage at silking (R1 stage). The control vs. clothianidin had a lower leaf area index at the 12th leaf (V12) stage (2.80 vs. 3.18) but similar values at R1 (4.59 vs. 4.76) and early grain‐fill (R3) stages (4.30 vs. 4.64 m2 m−2, respectively). The control vs. clothianidin had a lower mean crop growth rate from R1 to R3 (23.6 vs. 36.3) but similar rates from the V12 to R1 (34.9 vs. 36.4) and R3 to late grain‐fill (27.2 vs. 25.3 g m−2 d−1, respectively) stages. The control vs. clothianidin had less kernels per square meter (4423 vs. 4751) but similar kernel weight (257 vs. 248 mg) and harvest index values (0.48 vs. 0.49 kg kg−1, respectively). The control vs. clothianidin had lower yield (9.7 vs. 10.6 Mg ha−1, respectively), but root damage ratings did not correlate with yield (r = −0.19, n = 48). The relationship between corn rootworm damage and corn growth was subtle and inconsistent across growth stages, but the control consistently yielded 8 to 9% less than the clothianidin treatment.