Timing of Fungal Insecticide Application to Avoid Solar Ultraviolet Irradiation Enhances Field Control of Rice Planthoppers

SIMPLE SUMMARY: The control of rice planthoppers (RPH) in Asian countries has relied upon chemical insecticides for several decades. The reliance no longer continues in the rice–aquaculture coculture and rotation systems emerging as high-profit agriculture in Southern China because chemical control is prohibited in these systems to prevent aquaculture products from contamination with chemical residues. In this field study, the RPH population in three rice–shrimp rotation paddy fields was effectively controlled for four weeks at the critical tillering to flowing stages after two fungal insecticides were sprayed twice at the recommended rate. For either fungal insecticide, the sprays applied after 5:00 p.m. to avoid solar UV irradiation were consistently more efficacious against the RPH population than those before 10:00 a.m. These results indicate the feasibility of fungal insecticides for RPH control in the rice–shrimp rotation fields and the importance of timing the application of fungal insecticides to avoid solar UV exposure for enhanced RPH control during the summer months. ABSTRACT: Thechemical control of rice planthoppers (RPH)is prohibited in annual rice–shrimp rotation paddy fields. Here, the fungal insecticides Beauveria bassiana ZJU435 and Metarizhium anisoplae CQ421 were tested for control of RPH populations dominated by Nilaparvata lugens in three field trials. During four-week field trials initiated from the harsh weather of high temperatures and strong sunlight, the rice crop at the stages from tillering to flowering was effectively protected by fungal sprays applied at 14-day intervals. The sprays of either fungal insecticide after 5:00 p.m. (solar UV avoidance) suppressed the RPH population better than those before 10 a.m. The ZJU435 and CQ421 sprays for UV avoidance versus UV exposure resulted in mean control efficacies of 60% and 56% versus 41% and 45% on day 7, 77% and 78% versus 63% and 67% on day 14, 84% and 82% versus 80% and 79% on day 21, and 84% and 81% versus 79% and 75 on day 28, respectively. These results indicate that fungal insecticides can control RPH in the rice–shrimp rotation fields and offer a novel insight into the significance of solar-UV-avoiding fungal application for improved pest control during sunny summers.