Efficacy of increased azadirachtin doses against Diabrotica virgifera virgifera larvae in highly infested maize fields

The western corn rootworm (Diabrotica virgifera virgifera LeConte) is a significant maize pest in Hungary, particularly in monoculture systems. As many effective synthetic soil insecticides and seed dressings have been withdrawn, interest in environmentally friendly alternatives has grown. Among these, azadirachtin - an insecticide from the neem tree (Azadirachta indica) - offers long-lasting protection and reduced risk of resistance. We conducted multi-year field trials using seed-applied azadirachtin at doses ranging from 50% (0.022 mg/seed) to 300% (0.129 mg/seed), with 100% (0.043 mg/seed) as our previously recommended rate. In fields with moderate larval pressure, doses of 125-150% (0.053-0.065 mg/seed) prevented economic loss, although minor root damage occurred. In 2022, higher doses (200% and 300%) were tested under severe infestations (modified Iowa scale 3.93-5.10). Across sites, the 200% dose (0.086 mg/seed) showed the most favourable overall performance, reducing larval numbers and root damage while providing the best overall balance of efficacy and crop safety under high infestation pressure. In contrast, the 300% dose delayed development, likely due to poor germination under drought conditions, as the oil-rich formulation hindered water uptake. These findings underscore the need to tailor dosing to local conditions. Azadirachtin seed dressing is an effective and sustainable alternative to synthetic insecticides, with the 200% dosage showing the most favourable overall balance of efficacy and crop safety under high pest pressure.