The effectiveness of the neem product TreeAzin® in controlling Cameraria ohridella (Lepidoptera: Gracillariidae: Lithocolletinae)

Infestation by invasive horse-chestnut leaf miner, Cameraria ohridella Deschka & Dimić, permanently lowers the aesthetic and cultural value of horse-chestnut in Central Europe. In 2017-2018, in urban zones in the cities Parchovany and Strážske in the eastern part of Slovakia, we assessed the efficacy of systemic applications of TreeAzin®, an azadirachtin-based product, in controlling Cameraria ohridella in trials in which it was microinjected into tree trunks. A total of 16 Aesculus hippocastanum trees were treated with 3 ml of TreeAzin® per centimetre diameter at breast height [DBH] and another 17 were treated with 5 ml of the same product per centimetre at DBH, at two study plots. In total, 18 trees were left untreated as controls. In this field experiment, we confirmed significantly higher efficacy in the year of application and the following season. Statistically significant differences were found in the average leaf damage caused by C. ohridella, between treated (4.2-24.5% avg. leaf damage) and untreated trees (75.5-94.3% avg. leaf damage). At the end of the first growing season, 81.2-95.0% of the untreated control tree crowns were defoliated while defoliation of the treated trees was 19.2-31.6%. Both the 3 and 5 ml/cm doses were equally effective in terms of crown and leaf damage; no statistical differences were found in average leaf and crown damage between trees treated with doses of 3 ml/cm and 5 ml/cm. Similar results were also obtained the following year. Leaf damage of treated trees was 40.4-16.8% and of untreated trees 67.9%. Crown damage of treated trees was 49.7-59.8% and of untreated trees 78.8%. During the period of this study, the crowns of all the treated trees were statistically and visually healthier and fuller than those of untreated trees. Thus, the efficacy of this systemic insecticide in controlling C. ohridella in Europe is very promising and provides a suitable treatment for reducing the incidence of this invasive pest.