Control of citrus flat mites in pomegranate, 2023

Citrus flat mite is a common pest of pomegranate in California. Feeding on the fruit results in a brown scabbing or leathering (‘alligator skin’) that looks similar to sunburn. Damage is initially found at the stem end of the fruit and progresses downward as the severity increases, causing reductions in yield and quality. During 2023, we conducted 2 commercial field trials in northwestern Kern County, near Lost Hills, CA, to evaluate the effects of miticides on citrus flat mite density from Jun until Oct. Each trial was organized as an RCB design with 5 replications of 4 treatments and an untreated check using single-tree plots (Tables 1 and 2). Each plot was separated by a 1-tree buffer. Applications were made on 14 Jun using a gas-powered wand sprayer calibrated to deliver 200 gpa of spray solution using a TeeJet D6 orifice disc nozzle at 150 psi. All treatments were made with the addition of the surfactant Dyne-Amic at a rate of 16 fl oz per 100 gallons of water (0.125%) except Microthiol Disperss (sulfur). The efficacy of treatments was evaluated prior to treatment on 5 Jun, and then 2, 4, 6, 8, 11, and 13 wk after treatment (WAT) by collecting 10 fruits per plot, transporting them to a laboratory, and inspecting them under magnification for the number of citrus flat mites on each fruit. On 13 Sep and 5 Oct, 10 random fruit from each plot were each given a rating for scarring with a 0 equal to no scarring, 1 equal to initiation of scarring, 2 with scarring on at least 50% of the attachment end of the fruit, 3 with the entire attachment end with scarring, and 4 with the entire fruit scarred. The average numbers of mites per fruit in each plot, and average fruit scarring rating in each plot, were evaluated by ANOVA with means separated by Fisher’s Protected LSD (0.05) following a square root transformation of the data to normalize variances.

The Zeal, Onager, Envidor, and Microthiol Disperss treatments resulted in significant reductions in mite density on at least 3 of the 4 evaluations from 6 to 13 WAT in both trials compared to the untreated check (Tables 1 and 2). Envidor resulted in significantly lower mite densities compared to the other treatments and the untreated check 13 WAT. Levels of fruit scarring were consistent with the number of citrus flat mites present in fruit evaluations (Table 3). Scarring of fruit was significantly lower in all treated plots compared to the untreated check during both evaluation dates within both trials. Envidor resulted in significantly lower fruit scarring compared to all other treatments. Fruit scarring in plots treated with Onager and Zeal was significantly lower than the untreated check on all evaluation dates, and statistically equivalent to the industry standard of Microthiol Disperss.¹

Footnotes