The Effect of Nexter on California Red Scale Populations in Sweet Orange, 1999

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P. A. Stansly, J. M. Conner, and D. R. A. Peach
University of Florida/ IFAS
Southwest Florida Research and Education Center

Orange: Citrus sinensis (L.) ‘Murcott'
California red scale (CRS) Aonidiella aurantii (Maskell)

Recent increases of California Red Scale have been observed in several groves in southwest Florida especially those that recently used Nexter to control mites. Our objective was to monitor populations of CRS under different application scenarios of Nexter and in comparison with an industry standard. An 18 acre block of sweet orange ‘Murcott' with 80 tree rows orientated north to south was divided into 4 row plots with 3 replications. Four treatments were assigned to each 4 row plot in an RCB design. The time and number of applications of Nexter varied. All applications on 9 Jun included zinc and manganese at 1 lb/ acre and copper at 4 lbs per acre as a tank mix. Treatments were applied with an airblast sprayer at 125 gpa. Evaluations were made using pheremone traps and scale counts on fruit. The first 3 evaluations were conducted in the field using a 5x magnifying headset to count all armored scales on each of 4 randomly-chosen fruit at each of 5 locations in the center 2 rows of each plot. The last 2 evaluations were conducted in the laboratory by removing the same number of fruit and counting all scale under a stereoscopic microscope. Two additional fruit from each plot, chosen for high scale counts, were held for 21 days in 1 pint cardboard ice cream containers. Emerged parasitoids were counted after 20 days incubation at ambient temperature. A pheremone lure (Trécé, Salinas CA) was attached to the center of a folded 6"x12" yellow sticky trap (Olson Products, Medina Ohio) placed centrally in the middle row of each bed. The traps were removed after 3-6 days and the CRS males were counted by placing a template with six 2.26 cm2 circles on each side of the trap, measuring a total area of 27.2 cm2. A t-test was used to test for significant treatments effects for the first 3 evaluations where treatments consisted only of treatment with Nexter versus treatment with AgriMek. Data gathered subsequent to the second Nexter treatment was subjected to analysis of variance with mean separation by Fisher's LSD.

Density of male scales was consistent among treatments on 2 and 9 Sep. On 4 Nov. there were also no significant differences among treatments although 6 times more scales were seen on traps in plots treated with Nexter in Jun and Sep compared to those treated in June only. Highly significant differences were observed in numbers of CRS on fruit from trees treated with Nexter compared to those treated with AgriMek and oil. Observations in the laboratory following the second (Sep) treatment indicated significantly more CRS on fruit randomly sampled from trees sprayed both in Jun and Sep compared to all other treatments, with no differences among the other treatments. CRS observed fruit incubated for parasitoid emergence was more numerous on fruit from trees sprayed with Nexter on both dates, although there were significantly more from the Jun only treatment compared to the control on both dates. Percent parasitoid emergence from fruit collected on 15 Nov was highest from trees sprayed with Nexter in Jun and lowest from trees sprayed with Nexter in Sep. Thus, Nexter appeared to induce a notable although temporary increase in CRS population, which might have been caused by an incidental reduction in parasitoid activity.

Florida Agricultural Experiment Station Journal Series No. N-02008.

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