Seed-applied insecticides inconsistently affect corn forage in continuous corn

Western corn rootworirn (Diabrotica virgifera virgifera Le Conte) is the major insect pest in the corn phase of a corn (Zea mays L.) silage-perennial forage rotation. Dairy producers may prefer seed-applied instead of soil-applied insecticides for rootworm control because of ease of use and additional control of some other soil insect pests. The objective of the 2-yr NY field study was to evaluate clothianidin [(E)1-(2-chloro-1,3-thiazol-5-ymethyl)-3-methyl-2 nitroguanidine] and thiamethoxam (3-[(2-chloro-5-thiazolyl)methyl]tetrahydro-5-methyl-N-nitro4H-1,3,5-oxadiazin-4-imine) at the 1.25 mg a.i. kernel(-1) rate for rootworm control, dry matter (DM) accumulation, DM yield, and silage quality. The control had moderately severe (1.40-node injury scale), whereas clothianidin (0.18) and thiamethoxam (0.39) had acceptable rootworm damage ratings. Clothianidin had greater DM accumulation at the 12th leaf stage (384 g m(-2)) compared with thiamethoxam and the control (324 g m(-2)), greater DM accumulation 3 wk after silking (1491 g m(-2)), and greater DM yield (18.5 Mg ha(-1)) compared with the control (1245 g m(-2) and 17.0 Mg ha(-1), respectively). Thiamethoxam had similar DM yield (17.4 Mg ha(-1)) but greater milk Mg-1 (1559 kg Mg-1) compared with clothianidin (1475 kg Mg-1). Clothianidin had greater calculated milk yield (27,301 Mg ha(-1)) compared with the control (25,411 Mg ha(-1)) but similar to thiamethoxam, (27,192 Mg ha(-1)). Clothianidin and thiamethoxam provided acceptable rootworm control in this study but more research is required to determine if these results are consistent across different environments in the Northeast United States.