Citrus Thrips Insecticide Trial and Effects on Predacious Mites, 2015*

A field trial was conducted in a 13-yr-old ‘Washington’ navel orange orchard at the Lindcove Research and Extension Center, Exeter, California to compare the efficacy of various insecticides on citrus thrips and their effect on the predatory mite Euseius tularensis. Insecticides were applied on 17 Apr 2015 and a second application was applied on 4, 5, or 6 May. Treatments were diluted in 200 gal of water per acre and applied to trees in a RCB design to four blocks of four-tree plots using a 100-gal high-pressure D30 diaphragm pump sprayer with mechanical agitation. All treatments were applied with 0.50% Omni 6E oil, except for Veratran D, which required no oil and Movento was applied with 0.75% oil. All outside fruit within reach on each tree (mean 30–54/tree) were evaluated on 2 Jul 2015. Fruit were rated 0, 1–2 (slight) and 3–4 (severe) for levels of thrips scarring and the mean % total fruit scarred and % severely scarred were calculated. The predatory mites were sampled by randomly collecting four leaves from around the periphery of the tree and counting motile stages on the underside of the leaf and the mean number per leaf calculated. Treatment means were compared using ANOVA and means were separated according to Fisher’s LSD test (P = 0.05) after log₁₀ (x + 1) transformation of the numbers of predatory mites and arcsine(squareroot (x)) transformation of the proportions.

The untreated control fruit had 26.9% total thrips scarred fruit and 6.1% severely scarred fruit (Table 1). All treatments significantly reduced the percentage of severely scarred fruit compared to the untreated control, except for Movento and Bexar. Delegate, Agri-Mek, Exirel and Minecto Pro reduced the percentage of severely scarred fruit below 1.0%. Other products resulted in 1.2–3.7% severely scarred fruit.

All insecticides significantly reduced predatory mites on 4 or more dates during the sampling period compared to the untreated control and the severity of the effect increased after the second application of insecticides (Table 2). Bexar, Agri-Flex, Delegate and Minecto Pro reduced predatory mites below 0.5 mites per leaf (the threshold needed to assist with citrus thrips control) on three or four dates during 30 Apr–28 May.

Author notes