Holm oak leaf-mining moths

What are holm oak leaf-mining moths?

Leaf-mining moths are tiny moths with caterpillars that feed inside the leaves, creating discoloured blotches and meandering lines where the internal tissues have been eaten away.

Symptoms

• The more widespread leaf miner on holm oaks is Phyllonorycter messaniella.
• This causes pale brown, elongate oval discoloured areas on the upper leaf surface where caterpillars have eaten out the internal leaf tissues.
• The underside of these mines is whitish brown and is often torn open.
• On evergreen oaks, the damage remains visible until the old leaves drop in early summer.
• Another species of leaf-mining moth on holm oak, Ectoedemia heringiella, causes brown linear mines that end in a blotch. This is mainly in the London area, where it was first discovered in 2002, but is becoming more widespread. As with the other leaf miner on holm oak, the tree’s appearance is at its worst during spring.

Control

Non-chemical control

• Fortunately, holm oaks tolerate the damage and continue to grow, even when heavily infested.
• The appearance of the tree will improve in early summer, when new foliage develops and some of the old mined leaves have been shed.

Chemical control

• No insecticides likely to control these leaf miners are available to home gardeners.
• It is also very difficult to deal with pests on large mature trees.

Biology

• The tiny leaf-mining moth, Phyllonorycter messaniella has three generations a year.
• Larvae feed within the leaves during July, October, and from November to March.
• When fully fed, the larvae pupate within the leaf mines.
• By late winter, much of the foliage on a holm oak may be affected.
• Mines caused by Ectoedemia heringella develop during spring and are fully formed by the end of May.