Seed-applied insecticides inconsistently affect corn forage in continuous corn

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Western corn rootworm (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-nitro-4H-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.

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