Paint-On Application of Acephate for Aphid Control on Crape Myrtle

Materials and Methods

One hundred and six seedling crape myrtle trees, Lagerstroemia indica, ranging in diameter from 3 mm (1/8 in) to 6 mm (1/4 in) at 15 cm (6 in) above the soil line, were planted in two rows on 1 meter (3 ft) centers on February 27,1986 at the LSU Hammond Research Station, Hammond, Louisiana.

On August 26,1986, after heavy aphid populations of both nymph and adults were present, 70 trees were selected for a randomized complete block (RCB) design with 5 blocks and 14 trees per block within two rows. Treatments consisted of banding a slurry of acephate (Orthene 75 S™) in water with either a 3 parts acephate:1 part water or 4 parts acephate:1 part water, (v:v ratio) completely around the trunk at 5 cm (2 in) from the soil line. The band width was determined by the mean stem diameter of the seedlings used which was 5 mm (1/5 in). A camel hair brush 6 mm wide was cut to deliver a width of 5 mm to encircle each trunk. The 3:1 or 4:1 rate was increased by doubling or tripling the width of the band (2x or 3x). Control trees within the two rows were banded once with a clean brush and water. Time required for banding was less than one minute per tree.

Aphid population counts were uniformly taken. Two leaves from each quadrant and two from the top, totaling 10 leaves, were examined from each plant. Both nymph and adult aphids were counted using a Donegan Optivision™ Glass Binocular magnifier.

On August 24,1987, after heavy aphid populations of both nymph and adults were present, 70 of the same trees were again selected for a RCB design with 5 blocks and 14 trees per block. Trunk diameters ranged from 16 mm (5/8 in) to 32 mm (1 1/4 in). The band width was determined by the mean diameter of the seedlings which was 24 mm. Consequently, a 25 mm (1 in) brush was cut to deliver a 24 mm wide band to encircle the trunk from 1 to 3 times as described above.

Treatment means for the experimental data were compared statistically at the P = 0.05 level using Dunnett’s One-tailed T test after being transformed on a log scale for normalized standard error and distribution.

Results and Discussion

The August through October 1986 data are inconclusive (Table 1). The control plants had the highest aphid populations. Fifteen days after treatments, the populations on the control plants dropped to 39 ± 15 aphids on the control plants and to less than one on all other treatments. The drop in aphid populations in the control plants may have been due, although not measured, to root absorption of acephate washed into the soil by rainfall and not from seasonal change in aphid populations. Both juveniles and mature crape myrtle trees on the station away from the treated area maintained high population pressure. On Sept. 10, however, there was a significant difference in aphid populations between control plants and treated ones. On Sept. 30, 20 days after treatments, counts were again made and there was no significant difference between control and treated plants.

The data from 1987 indicated a strong relationship between banding with acephate and aphid control (Table 2). On Aug. 24, just prior to treatments, the aphid populations were high. Aftertreatments, the aphid populations significantly dropped on the second date. The aphid population on control plants also dropped. One of the 2x, 4:1 treatments in block 1 was inadvertently omitted, which may have resulted in an unusually high population value on Sept. 9. All treatments except the one noted remained low through Sept. 16 which was over 23 days. By Sept. 21, one 2x and both 3x treatments still suppressed aphid populations, whereas populations in the two 1x and one 2x treatments increased slightly. On the last date counts were made, which was 37 days after treatment, aphid populations on all treatments were on the rise. Higher concentrations of acephate displayed some suppression of aphid populations, but the effect was not significant statistically. No phytotoxicity was observed as a result of any treatment.

Conclusions

Aphid control can be expected for up to a month using an acephate paint-on banding application on small trees. The authors believe it will be economically feasible to use this method instead of spraying. It’s faster to prepare and apply and there is no tank or spray equipment to clean afterwards. Also by placing acephate directly onto the trunk, one reduces spray drift of the product, especially in crowded urban environments.

After applying the product as a paint-on band around the trunk, a whitish residue remains obvious until rainfall washes the residue from sight. The authors therefore recommend that the band be placed six inches from the soil line to lessen the likelihood of human or pet exposure. The authors recommend that after registration of Orthene 75 S™, which is expected in the Spring of 1992, applicators should use neoprene rubber gloves, and goggles or a face shield when applying the band. Avoid direct skin contact and, if clothing is contaminated with the product, wash separately from other clothing.

(Note: This paper reports the result of research only, and does not imply registration of a chemical under amended FIFRA. Before using the test product mentioned in this research report, be certain of its registration by appropriate state and/or federal authorities.)