Efficacy of Soil and Trunk Applied Systemic Insecticides for Three Years After Application for Control of Emerald Ash Borer (Coleoptera: Buprestidae) on Green Ash^*

We evaluated the efficacy of two formulations of emamectin benzoate applied as trunk injections, and imidacloprid applied as a soil drench for control of emerald ash borer (EAB) (Agrilus planipennis Fairmaire) for 3 years following application. A 0.2-ha plantation of ash (Fraxinus) species was established in May 2003 at the Michigan State University’s Tollgate Education Center in Novi, MI. On 15 May 2012, green ash (Fraxinus pennsylvanica) with trunk diameters averaging 15.2 cm at breast height were treated with 4% emamectin benzoate (TREE-age®; Arborjet, Woburn, MA), a novel formulation of 4% emamectin benzoate (ARBORMECTIN™; Rotam Agrochem International Co. Ltd., Hong Kong, China), or imidacloprid (Xytect® 75 WSP; Rainbow Treecare Scientific Advancements, Minnetonka, MN). Emamectin benzoate formulations were applied as trunk injections at a rate of 10 ml/in. trunk diameter using the Arborjet Tree I.V system with #4 Arborplugs® (Arborjet, Woburn, MA). Imidacloprid was applied as a soil drench (Table 1) at a rate of 1.4 g active ingredient per inch trunk diameter. The experiment was designed as a randomized block with five replicate trees per insecticide treatment and six replicates for the untreated control.

Treatments were evaluated on 26 Jun 2013 and 15 Aug 2014 by visually rating the degree of canopy dieback on a 1–5 photographic rating scale with 1 showing no signs of decline and 5 being dead (Klooster et al. 2014, Biol. Invas. 16:859–873). Trees were assessed independently by two evaluators and the ratings averaged to generate a single value for each tree. Number of adult exit holes were recorded on 4 Jun 2013 and 15 Aug 2014. Trees were harvested on 15 Aug 2014, and a trunk section 183-cm in length from the ground was subsequently debarked with a draw knife, and the number of living larvae were recorded. Data were analyzed via ANOVA; Number of larvae per tree were transformed [ln(X + 1)] to increase homogeneity of variances. Number of larvae was the only variable for which the F-test from ANOVA was significant (P = 0.002) and means were separated using the Protected LSD test (P ≤ 0.05).

Treatment effects on canopy decline, number of exit holes and larvae per tree are presented in Table 1. All trees expressed very low or no signs or symptoms of infestation in 2012 and 2013. Hence, no conclusions could be reached about product efficacy during the first (2012) or second (2013) year following treatment. Quantifying the number of larvae per tree in Aug 2014 (infestation resulting from oviposition in 2014) provided an indication of efficacy in the third year following treatment. Number of larvae in trees treated with the two emamectin benzoate formulations did not differ in 2014, and were very low relative to untreated trees, which indicates that these treatments provided 3 years of control following a single application. However, due to high variation in the control, the difference between number of larvae in trees treated with Arbormectin and the untreated control was not significant. Trees treated with imidacloprid in 2012 had high numbers of larvae in 2014, indicating that imidacloprid did not provide control 3 years following application. There was no evidence of phytotoxicity for any treatment on any evaluation date.

Author notes