Evaluation of foliar insecticides for the control of onion thrips in dry-bulb onion, 2014 *

The objective of this experiment was to assess the efficacy of foliar insecticides applied at threshold levels for the control of immature stages of OT in dry-bulb onion. The trial consisted of 12 main effect treatments arranged in a randomized complete block (RCB) design with four experimental replicates. Onion was direct seeded on 5 May 2014 at Shiprock Farms, located 5.1 miles (8.1 km) west of Coloma, WI. Experimental plots consisted of 54 inch (1.4 m) raised formed beds containing 6 rows of onion spaced 9.8 inches (24.9 cm) between rows and 2.6 inches (6.6 cm) within rows. Experimental plots measured 25 ft (7.6 m) in length with planted beds on either side acting as guard rows. All foliar treatments were applied in 1.5 liters of water at an application rate of 20.2 gpa using a four nozzle, 6 ft (1.8 m) boom equipped with 8002XR flat fan spray tips powered by a CO ₂ backpack sprayer operating at 30 psi. Successive applications were initiated when mean immature thrips populations had exceeded established thresholds of three immature thrips per leaf. The foliar applications were applied on 29 July and 5 August. Application on 29 July occurred between 1030 and 1100 hours, and application conditions were recorded as northwest wind 13.9 mph (22.3 kph), 71.6°F (22°C) under partly cloudy conditions. Application on 5 August occurred between 10:30–11:00 h, and application conditions were recorded as northeast wind 9.2 mph (14.8 kph), 7.8°F (22.7°C) under partly cloudy conditions. All plots were maintained to standard commercial practices. Immature life stages of OT were assessed by counting the number of larvae on 10 plants in the central 2 rows of each plot. Larval counts occurred three times during the summer on 8 August (10 days after treatment (DAT)) after the first application, and again on 12 August (7 DAT), 19 August (14 DAT) after the second application. Count data were log ₁₀ transformed prior to analysis. Data were analyzed using ANOVA and means were separated with a Fisher’s protected LSD and data are illustrated ( Table 1 ). No overt signs of phytotoxicity were observed among any of the treatments.

Author notes