Deposition of aerially applied tebufenozide (RH5992) on Balsam fir (Abies balsamea) and its control of spruce budworm (Choristoneura fumiferana [Clem.])

A field trial was conducted in 1994 to determine the foliar deposit of tebufenozide (RH5992), applied aerially, and its efficacy against spruce budworm, Choristoneura fumiferana (Clem.). A commercial 240 g litre-1 formulation of the insecticide (Mimic 240LV) was mixed with water, dyed with a tracer dye (Rhodamine WT) and sprayed with a light fixed-wing aircraft. Six application strategies were tested. Five used 70 g AI ha-1 in a spray volume of 1 or 2 litre-1 ha-1 with single or double applications; the sixth was an unsprayed control. Results show that the spectra of the spray applications were, with one exception, fairly uniform. Volume and number median diameters ranged from 100 to 130 micrometer and 27 to 72 micrometer, respectively. Mean number of drops cm-2 on Kromekote cards were < 2.0 for strategies where either 1 or 2 litre ha-1 were sprayed. Nevertheless no one strategy produced droplet densities that were significantly different (P < 0.05) from the other strategies. Tebufenozide recovered from foliage averaged 2.5 to 5.9 microgram g foliage-1 when 1 litre ha-1 was sprayed and 5.8 to 6.8 microgram g foliage-1 after 2 litre ha-1 were sprayed. When a single application was the strategy used, the mean number of droplets cm-2 and microgram tebufenozide g foliage-1 ranged from 1.2 to 1.4 and 2.5 to 5.9, respectively. With double applications, the same response parameters ranged from 0.3 to 1.9 and 2.5 to 6.8, respectively. Budworm population reductions (%) and the number of larvae that survived tebufenozide treatments were significantly different (P < 0.05) from the controls. After strategies that used 1 litre spray ha-1, mean percentage population reductions ranged from 61.4 to 93.6 whereas populations were reduced by 85.6 to 98.3% when 2 litre ha-1 were sprayed. After double applications the mean percentage population reductions ranged from 93.6 to 98.3, but single application strategies resulted in mean reductions of 61 to 86%. Mean population reductions in the controls were 61%. The mean number of larvae per branch that survived spray strategies of 1 litre ha-1 ranged from 1.3 to 7.4, and from 0.4 to 1.3 when 2 litre ha-1 was the spray volume. In the controls an average of 10.2 larvae survived. With one exception, mean percentage defoliation in the treated areas was also significantly less (P < 0.05) than that in the control. Mean defoliation in trees sprayed at 1 litre spray ha-1 ranged from 40 to 62.8% whereas those treated at 2 litre ha-1 had mean defoliation levels from 31.5 to 62.8%. In contrast, average defoliation in the controls was 92.1%. When a single application was the spray strategy, mean defoliation ranged from 31.5 to 62.8%. These data imply that a double application of tebufenozide at 70 g in 2 litre ha-1 was the most efficacious strategy. However, analyses of the data also show that the primary influence on deposits and defoliation was interactions between number of applications and spray. Nevertheless the two independent variables acted without significant interactions when influencing percentage reductions of spruce budworm populations.