Insecticidal Control of Crapemyrtle Bark Scale on Potted Crapemyrtles, Fall 2018

The purpose of this study was to determine the relative efficacy of several insecticides to control crapemyrtle bark scale on 3-gal container-grown crapemyrtle plants. The trial was conducted between 11 May and 21 November 2018 on a nursery pad at the Texas A&M AgriLife Research & Extension Center in Overton, TX. Crapemyrtle plants were artificially infested by haphazardly tying crapemyrtle bark scale-infested branches (1″–4″ long) onto the potted crapemyrtle plants in the Fall of the previous year. CMBS density on plants was assessed using two methods: sticky traps and visual counts. Sticky traps were made using double-sided sticky tape (3/4 ″ Scotch Permanent Double-Sided Tape; 3M, Maplewood, MN) wrapped around 2–3 branches per plant. Tape was removed 1 wk later and counts were made in the laboratory of the number of crawlers/sq. cm of double-sided sticky tape using a dissecting microscope. The sticky tape traps the first life stage of CMBS that emerges from the eggs, known as crawlers, due to their high level of mobility. Timing of the tape-trap deployment was to coincide with predicted peaks in crapemyrtle bark scale abundance based on the last 3 yr of field trapping data (data not shown). Visual field counts were made of all live male pupae and live female egg sacs from each plant. Treatments were assigned to plants in a CRD with six replications (individual plants) per treatment. All treatments were made as foliar spray applications using a R&D CO₂ sprayer (Model D-203S) fitted with a 601FA single nozzle spray boom (Bellspray, Inc., Opelousas, LA) until runoff (Table 1). Phytoxicity and sooty mold coverage (0–100%) per plant were also assessed during every field observation. Scale crawler counts were averaged for all tapes within a plant and then compared between treatments within sampling period using the Wilcoxon signed-ranks test and Dunn with Control for Joint Ranks post hoc test, with untreated check as the control. Male pupae, female egg sacs, and sooty mold coverage data were log-transformed data (log(x+1)) and compared using ANOVA (P < 0.05) and Dunnett’s post hoc test with untreated check as the control group.

At 15 WAT, Distance (positive check) had significantly lower crawlers than the untreated check (Table 2). Looking at maximum number of crawlers (Table 2), we also find Altus (10.5 fl oz/100 gal), Cyclaniliprole (22 fl oz/100 gal), Talus, and Safari to have substantially (>75% reduction) lower maximum crawlers than the untreated check at 15 WAT (Table 2), despite lack of statistical significance.

The number of male pupae was significantly lower on Altus (10.5 fl oz/100 gal), IKI-3326SL (12 fl oz/100 gal), Safari, and Distance-treated plants at 9 WAT compared with plants in the untreated check (Table 3). By 20 WAT, Altus (10.5 fl oz/100 gal), Cyclaniliprole (22 fl oz/100 gal), Talus, and Distance-treated plants had significantly fewer male pupae compared with plants in the untreated check (Table 3). Safari (4 and 6 WAT), Altus (10.5 fl oz/100 gal; 6 WAT), and Talus (6 and 9 WAT)-treated plants had significantly fewer CMBS egg sacs compared with the untreated check (Table 4). By 20 WAT, Distance, Safari, Talus, and Altus (10.5 fl oz/100 gal)-treated plants had much lower numbers (at least 75% reduction) of CMBS egg sacs compared with the untreated check, but these differences were not statistically significant (Table 4). There were no significant differences in sooty mold coverage (data not shown) among treatments.

High variability in the initial infestation levels among plants may have accounted for the lack of statistically significant differences among treatments in some cases. No phytotoxicity was observed for the duration of the trial.

This research was supported by IR4, USDA National Institute of Food and Agriculture (grant no. 2017-51181-26831/1013059), industry funds, and gifts of pesticides.