Foliar and Drench Insecticides for Preventative Control of Crapemyrtle Aphid, 2017

This study tested the efficacy of preventative drench and foliar insecticide treatments for protecting ‘Hopi’ crape myrtle, Lagerstroemia indica L. x fauriei Koehne, from crapemyrtle aphid, Sarucallis kahawaluokalani (Kirkaldy). The study was performed in a greenhouse at the Tennessee State University Nursery Research Center, McMinnville, TN. In Mar 2017, rooted cuttings were established in 1-gal containers in pine bark mulch media. Plants were fertilized with the medium rate of 18-6-12 Osmocote Classic and maintained with drip-line irrigation. Crape myrtles were periodically sprayed with horticultural oil as a low-residual measure to manage arthropod pests.

Experimental plants were assigned to the chemical treatments in Table 1. The foliar Altus treatment was sprayed to runoff with a backpack sprayer (Solo, Newport News, VA) and plants in the drench treatments received 12.8 oz of solution (10% container volume) applied across the media surface. The experimental plants were arranged on a greenhouse bench in an RCB design with six replicates. Twenty-four hours after chemical applications, a leaf disc with 10 immature aphids was placed in the canopy of each experimental plant. At 0, 7, 14, 21, 28, 35, and 42 DAT, the newest, fully expanded leaf was sampled from the central leader of each experimental plant and aphid adults and immatures were counted. Adult and immature counts were analyzed independently with a generalized linear model fitted to a negative binomial distribution (PROC GENMOD, SAS Institute Inc.). Post hoc tests were performed with a Tukey–Kramer test with P values adjusted for multiple comparisons.

Low numbers of adult (Table 2) and immature (Table 3) aphids were found on the experimental plants at 0 DAT and no significant difference between any of the treatments was observed. Adult aphids were not observed on any of the treatments at 7 DAT. From 14 DAT through 42 DAT, the Aria drench and all three Altus treatments had significantly fewer adult aphids than the check. The Kontos drench treatment had fewer adult aphids than the check at 14, 21, and 28 DAT but was equal to the check at 35 and 42 DAT. All chemical treatments had significantly fewer immature aphids than the check at 0, 7, 14, 21, 28, and 35 DAT. The Kontos drench treatment had the same number of immatures as the untreated check at 42 DAT.

This research was supported in part by funding and materials provided by Bayer.