Control of Two Spotted Spider Mite, Sweetpotato Whitefly, and Melon Thrips with Predatory Mites, Metharhizium, and Insecticides on Eggplant, 2014 *

Spider mites are important and consistent pests of eggplant in south Florida where feeding damage often causes decline in the overall health of the plant, leading to lower yields. Sweetpotato whitefly can often build up extremely dense populations in eggplant, leading to plant decline and problems for other crops in the area. Melon thrips feeding can cause fruit scarring and flecking, leading to a reduction in fruit quality. For this trial, two single rows separated with a row of corn were prepared at the Southwest Florida Research and Education Center in Immokalee, FL, on raised beds. Granular fertilizer (10-2-10 N-P-K) was incorporated, and two drip tapes with emitters spaced at 8 inches and a flow rate of 0.67 gpm/100 ft were laid before covering with black polyethylene film mulch and fumigating through the drip with 300 lb/acre PicClor 60 EC. Greenhouse-raised plants were transplanted on 6 Mar at 24-inch spacing, and the remaining 50% required nutrients were delivered by drip irrigation as liquid 7-2-7. Plots contained 16 plants, with five plants between plots as a buffer and assigned across the two beds in an RCB design. Applications were made weekly ( Table 1 ) using a high-clearance sprayer operating at 180 psi and 2.3 mph with spray delivered through two vertical booms equipped with yellow Albuz® hollow cone nozzles, each of which discharged 10 gallons per acre from each nozzle ( Table 1 ). The predatory mites A. swirskii and N. californicus (Koppert Biological Systems, Howell MI) were released by sprinkling infested bran substrate onto the center 10 plants. Neoseiulus longispinosus originally obtained from Amy Roda, USDA-APHIS, Miami, FL, was released on 11 Apr by placing sorghum plants infested with banks grass mite Oligonychus pratensis and ∼80 L. longispinosus in the center of each treated plot. The five buffer plants were sprayed with a rotation of Abba Ultra (5.0 oz), Oberon (10.0 oz), and Baythroid XL (3.0 oz) on all spray dates to impede migration of predatory mites between plots. All stages of spider mites, whitefly, and predatory mites were monitored weekly from 23 Apr to 16 Jun by collecting a fully mature mid-canopy leaf from five plants in each plot of which 10, 0.5-inch ² discs were examined under a stereoscopic microscope. Treatment effects from each plot were analyzed using the SAS Mixed repeated measures procedure with treatment and sampling date as fixed factors and replicate and replicate × date as random factors. Data were log(x + 0.05)-transformed to normalize counts. Pairwise comparisons were assessed with Tukey-adjusted t-tests to when treatment effects were significant to control for overall experiment-wise error rates. All ripe fruit was collected on 21 May and 2 June from five plants in each plot and sorted into three categories: no damage, slight calyx damage, or severe calyx damage and scarred fruit. Harvest data were analyzed by ANOVA with mean separation by LSD ( P  < 0.05) contingent on a significant treatment F.

Predatory mites migrated to all plots despite the insecticide barrier applied to buffer plants. However, significantly more were found through 19 May on plants receiving the mites initially, after which their distribution followed the same trend but with less regularity ( Table 2 ). Most preimaginal stage whiteflies were found on untreated plants through 19 May, although differences with NBZ2166 + Induce were generally not significant ( Table 3 ). Fewest whiteflies over all dates were seen on plants receiving predaceous mites, either alone or with NBZ-2166. Spider mites built to high numbers through 27 May in the untreated check, declining afterward ( Table 4 ). Enormous numbers were seen on untreated plants through 2 June, after which they diminished by an order of magnitude ( Table 4 ). Fewest spider mites were seen over dates on plants treated with Oberon alternated with Abba Ultra + JMS stylet oil, although not significantly fewer than on plants receiving NBZ-2166 alone on 7, 19, 27 May or 16 June. Thrips numbers were much lower and peaked earlier than spider mites but also declined precipitously late season ( Table 5 ). The fewest thrips were seen in pesticide plots over all dates, followed by the remaining three treatments which did not differ from each other. However, differences with the pesticide rotation treatment were not significantly different than one or more of the other treatments from 7 May onward. Most undamaged fruit was harvested from plants sprayed with Oberon alternated with Abba Ultra + JMS stylet oil, but plants receiving predaceous mites plus sprays of NBZ2166 52 EC had more than the untreated check ( Table 6 ). All treatments reduced severe calyx damage and all but NBZ2166 alone reduced fruit scaring; the least scarring was seen with the rotation. No phytotoxic effects were seen observed.

Author notes