Control of Onion Thrips, Seeded Onions, Ft. Collins, Colorado, 1985

Onions, cv Brown Beauty, were seeded 2-3 Apr in a field under furrow irrigation at the Colorado State Univ Bay Farm in Fort Collins, Colorado (Larimer Co.). Plots were 8 × 30 ft and treatments were arranged in a randomized complete block design with 4 replications. Treatments were applied with a CO2 hand sprayer delivering 48 gal/acre at 30 psi or were broadcast (Diazinon). Initial application of all insecticides in the test was made 31 Jul (Trial #1). Additional applications, made if mean number of thrips exceeded 10 per plant over all 4 replications in prespray counts, were 20 Aug (Trial #2) and 28 Aug (Trial #3). Evaluations, made by counting the number of nymphs and adults on 10 plants in each plot, were: Trial #1-31 Jul (prespray), 2 Aug (2 day), and 7 Aug (7 day); Trial #2-16 Aug (prespray), 23 Aug (2 day); Trial #3-23 Aug (prespray), 30 Aug (2 day). Percent control was adjusted based on prespray counts in both treatment and control plots. There was no insecticide application prior to the test.