Introduction: Two insecticide trials were conducted at the Western Colorado Research Center at Fruita to evaluate several classes of insecticide against onion thrips. The first trial evaluated methyl anthranalate, an insect feeding stimulant, with each insecticide. The second trial evaluated Lannate LV and Spinosad in combination with surfactants or methyl anthranalate.

Insecticide Trial I

Crop: Onions: 'Teton'

Target insect: Onion thrips, Thrips tabaci

Application dates: June 30 2003, July 7, 2003

Sprayer: Hand held, CO₂ pressured, calibrated to apply 16 gal/A

Plot size: 15 ft x 3- 30 inch beds, with two seed rows per bed

Sampling: Five onions were chosen from the center of each plot, and thrips extracted in Berlese funnels for 24h. All thrips were separated by growth stage. Samples were taken on July 5 (5 days after treatment), and again on July 14 (14 days after initial treatment and 7 days after 2nd treatment).

Results: Treatments and results are presented in Table and Figures 1 & 2. There were no significant differences between treatments on the first sample date although thrips numbers in Lannate LV and Spintor treatments appear lower than other treatments. On the second sample date, Lannate LV performed better than any other insecticide, which is consistent with 2002 results. Lannate LV was the only insecticide to reduce thrips numbers compared to the untreated control on the second sample date. Methyl anthranalate did not significantly improve the performance of any insecticide.

Table 1. Results from Insecticide Trial I.

¹ MA - Methyl anthranalate is a food grade spray additive add to determine if it improves insecticide efficacy

Means within a column followed by the same letter are not significantly different (LSD =0.05).

Insecticide Trial II

Crop: Onions, ' Teton'

Target insect: Onion thrips, Thrips tabaci

Application date: July 18, 2003

Sprayer: Hand held, CO₂ pressured, calibrated to apply 16 Gal/A

Plot size: 15 ft x 3-30 inch beds, with two seed rows per bed

Sampling: Thrips were counted in the field on five onions per plot. Onions in the middle bed of the three bed plots were counted. Thrips were visually separated into adult and immature classifications. Plots were sampled on July 22 (4 DAT), 23 (5 DAT), and 24 (6 DAT).

Table 2. Treatment rates in Insecticide Trial II

Table 3. Results from Insecticide Trial II.

Results. Treatment rates are presented in Table 2. Sample results are displayed in Table 3. There were no differences among treatments at 4 DAT although immature thrips counts appeared lower in all treatments than in the untreated control. Several treatments reduced the number of adult onion thrips compared with the untreated control at 5 and 6 DAT. There was no significant increase in insecticide when combined with any spray additive. Untreated plants in areas away from the insecticide plot were sampled on each sample date. It is interesting to note those plants had much higher OT counts than the untreated plants within the plot area. If the untreated field counts are compared with treated plots, it is apparent that both Lannate and Spinosad treatments were effective at reducing thrips numbers (Figure 3).

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Acknowledgements: Melissa Foley assisted with insecticide application of both experiments and sampling of trial I. Leonard Askham and Harriot Hagedorn sampled trial II. The staff of the Western Colorado Research Center at Fruita assisted with maintenance of the onion field. These trials were funded in part by a grant from the Colorado Onion Association.