The influence of systemic inducing agents on horse chestnut leaf miner (Cameraria ohridella) severity in white flowering horse chestnut (Aesculus hoppicastanum L.)

- The insecticidal efficacy of three systemic inducing (SIR) agents against horse chestnut leaf miner (Cameraria ohridella, HCLM) was assessed.
- The effectiveness of each SIR inducing agent on HCLM severity increased when applied at increasing frequencies.
- Efficacy of SIR inducing agents was in the order potassium phosphite>salicylic acid derivative>harpin protein>water control.
- SIR agents reduced leaf mining activity by 35-64%.
- The synthetic insecticide deltamethrin provided the greatest degree of leaf miner control with two foliar sprays providing 100% HCLM control.
- Enhancement of leaf phenolic content was indicated as a means by which SIR agents reduced HCLM activity.
- Results show commercially available SIR inducing agents exist that provide potentially acceptable degrees of HCLM control.

Two separate trials during 2010 and 2011 were conducted using field grown white flowering horse chestnut trees (Aesculus hippocastanum L.) to asssess the insecticidal efficacy of three systemic inducing agents (SIR), namely (Messanger (active substance (a.s.) Harpin protein), Phoenix (a.s. Potassium phosphite) and Rigel (a.s. Salicylic acid derivative) applied to coincide with the appearance of each adult generation of the insect pest, horse chestnut leaf miner (Cameraria ohridella Deschka and Dimic; HCLM). A conventional synthetic insecticide (deltamethrin) used within the UK for HCLM control was included for comparison. A marked impact of SIR inducing agent and frequency of application on HCLM severity was recorded. The effectiveness of each SIR inducing agent on mean number of HCLM mines per leaf and percent HCLM larvae/pupae mortality increased when applied at increasing frequencies i.e. three sprays provided greater control than two sprays while two sprays provided greater control than one spray. The synthetic insecticide deltamethrin provided the greatest degree of HCLM control with two foliar sprays providing 100% HCLM control. Efficacy of SIR inducing agents based on reduction of HCLM mines per leaf after three sprays averaged across both the 2010 and 2011 growing seasons was in the order potassium phosphite > salicylic acid derivative > harpin protein > water control where leaf mining activity was reduced by 35-64%. Enhancement of leaf phenolic content was indicated as a means by which SIR agents reduced leaf mining activity. Results show commercially available SIR inducing agents exist that provide potentially acceptable degrees of HCLM control provided at least two sprays are applied during a growing season.