Trials offer hope of "benign" long-term control of leaf miner

Trials of leaf-sprayed biological stimulants suggest they could have a role in managing the damaging horse chestnut leaf miner (Cameraria ohridella).

Image: James Bowe (CC BY 2.0)
Image: James Bowe (CC BY 2.0)

Dr Glynn Percival, manager of the Bartlett Tree Research Laboratory at the University of Reading, and Berkshire arboricultural consultant Simon Holmes, assessed the efficacy of three "systemic inducing agents" (SIRs) and a conventional insecticide, deltamethrin, against the pest, which established itself in the UK's horse chestnut trees in 2008.

Percival had earlier assessed the three foliar treatments - Messenger (active substance harpin protein), Phoenix (potassium phosphite) and Rigel (salicylic acid derivative) - to control apple scab.

"The synthetic insecticide deltamethrin provided the greatest degree of HCLM control with two foliar sprays providing 100 per cent HCLM control," they found.

"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."

They concluded: "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."

Percival told HW: "I think the SIRs offer a more environmentally benign means of pest control, and the other advantage is that they can be applied as a root drench."

The laboratory has also funded a PhD student to look at SIR in combination with for example bio-control agents, he added.

"I believe with time a non-chemical control package can be developed that will offer long-lasting insect control. After all when we go abroad a single injection against diphtheria etc., lasts 10 years, [whereas] use of antibiotics lasts only as long as the course of the tablets - that's how I compare SIRs against conventional spray. Once the insecticide wears off the tree becomes re-infested."

The results are published in Urban Forestry & Urban Greening.

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