Evaluation of Systemic Pesticides as Preventative Treatments for Japanese Maple Scale, 2016–17

Lopholeucaspis japonica is problematic in southeastern nursery production. The scale has two generations per year and produces a white, waxy test that is difficult to remove from the bark of trees. Infestations negatively affect tree marketability. This study evaluated systemic drench applications of Mainspring, Acelepyrn, and Discus N/G as preventative treatments for L. japonica.

The study was carried out at Tennessee State University’s Otis L. Floyd Nursery Research Center in McMinnville, TN. Redbud liners acquired from the Tennessee Division of Forestry were transplanted in Mar 2016 into #3 containers (3-gal) with a pine bark mulch media. Containers were fertilized with the medium rate of 18-6-12 Osmocote Classic and maintained in a shade house with overhead irrigation. The rates and timing of drench applications can be found in Table 1. An 18 fl oz solution of each product was applied evenly around the base of the trunk. Irrigation was reduced for 1 wk postapplication to reduce the products leaching from the soil. To initiate L. japonica infestation, on 3 Jun 2016, five replicate trees per treatment were transferred to a field location directly under three 40 ft-tall, L. japonica infested red maples, Acer rubrum L. Experimental trees were arranged in five rows with 1 ft spacing within rows and 3 ft between rows in an RCB design. Additionally, experimental trees were artificially infested with 1.5 cm diameter bark cuttings taken from infested red maples with active crawlers. Bark cuttings were removed from densely infested portions of donor plants with a #10 cork borer and secured, infestation side down, loosely to the lower trunk of experimental trees with a wax paper wrap. A second artificial infestation on 15 Aug 2016 coincided with the observed peak crawler activity of the second generation of L. japonica. On 11 Oct 2016, the experimental trees were moved to a shade house to overwinter. On 20 Mar 2017, trunks were dissected under a microscope and counts and mortality of L. japonica were determined. Counts of live and dead scales were analyzed independently with a generalized linear model in SAS (Proc Genmod) under a negative binomial distribution and log link. Post hoc tests were performed with a Tukey–Kramer test with P-values adjusted for multiple comparisons.

Live and dead scales were observed on trees in the check and in each chemical treatment, with the exception of Discus N/G, in which no scales were found. No treatments, other than Discus N/G, have statistically fewer live or dead scales than the check. The mortality model was not significant due to the large amount of variation between replicates; however, Discus N/G, the pesticide standard, was the only treatment with no L. japonica infestation on any replicate at the end of the study. All remaining treatments had some level of infestation. The results indicate Discus N/G prevented crawler establishment and that Acelepryn and Mainspring were less effective relative to Discus. The variability observed in the Acelepryn and Mainspring treatments may be due to problems with movement of the active ingredients into the container media. After the project was initiated, the product manufacturers increased the recommended volume of water for successful drench applications. Further testing is needed to determine whether the efficacy of Acelepryn and Mainspring can be improved with the application of greater water volumes that more thoroughly drench the entire root zone.

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