Effects of pre-bloom application of insecticides on rind scarring damage caused by citrus thrips in 2024

A field trial was conducted in a 5-y-old ‘Tango’ mandarin orchard at the Lindcove Research and Extension Center, Exeter, CA, to evaluate the effect of pre-bloom application on citrus rind scarring caused by citrus thrips. The trial evaluated 10 management programs that include 2 to 3 insecticide applications made prior to bloom on 10 April or post-petal fall on 29 April or 13 May (Table 1). Treatments were diluted in 200 gal of water per acre and were applied using a 100-gal high-pressure D30 diaphragm pump sprayer with mechanical agitation at 250 psi. The water pH for Gargoil application was adjusted to 5.5 by adding citric acid before mixing the product. A 0.5% concentration of 415 Supreme Spray Oil was added to all products, except Gargoil and the stand-alone 415 Supreme Spray Oil treatment, as an adjuvant. The experimental design was an RCB with 3 blocks of 5-tree plots. Rind scarring was evaluated during the third week of July 2024 by rating a total of 100 (25 from four quadrants each) outer canopy fruits in each tree as 0, 1 to 2 (slight), and 3 to 4 (severe). In each plot, we also determined the number of thrips per 20 randomly selected fruits and the number of predatory mites on 20 inner canopy leaves. The mean percentage of fruit infested with thrips, total fruit scarred, and severely scarred fruit were calculated. Treatment means were compared using ANOVA and means were separated according to Fisher’s Protected LSD (P < 0.05). After logarithm (log10 (x + 1)) and arcsine (square root (x)) transformation of the mite number and proportions, respectively.

The trees with pre-bloom application of FujiMite SC had significantly higher severely scarred fruits compared to the control (Table 1). The other treatments had no significantly different percentages of total and severely scarred fruits, compared to the control. Overall results of the 2024 season showed that adding a pre-bloom application does not reduce thrips scarring damage.

There were no significant differences in the number of thrips on fruit on any evaluation date, with thrips presence only found in 3 treatments and the control on at least 1 evaluation date (Table 2). We observed a significantly lower number of predatory mites in all treatments on the final evaluation date compared to the control. Treatment programs containing a pre-bloom application FujiMite had the overall lowest predatory mite densities, highest percentage of thrips-infested fruit, and highest percentages of fruit scarring (Tables 1 and 2).

Funding

This research was supported in part by the Citrus Research Board with additional industry gifts of pesticides and funding.

Conflicts of interest. None declared.