What's eating my holm oak?

Holm Oak, common across Mediterranean Europe and planted widely in the UK, faces oak processionary moth in warmer regions, knopper gall wasps, tortrix moth caterpillars, and scale insects. Phytophthora root rot is a serious non-insect threat. Deer browse young trees. Generally robust, but OPM is a spreading concern in southern England.

Silk nests on trunk and branches; caterpillar hairs cause severe skin rash, eye irritation, and respiratory problems in humans and animals; defoliation in heavy infestations Report sightings to Forestry Commission (UK statutory pest); professional nest removal only — never handle; pheromone traps; Bt spray on young larvae before nest formation

Acorns deformed into ridged, sticky green galls; seed inside destroyed; can reduce acorn crop significantly in affected stands No practical control; remove galled acorns from ground to reduce next-generation population; tolerate as cosmetic/crop issue

Leaf rolling and feeding in late spring; fresh leaves spun together with silk; defoliation of shoot tips; trees usually re-flush but growth is set back Bt spray when caterpillars are small (May–early June); encourage natural parasitoid populations; no intervention needed on healthy established trees

Brown oval scales on bark; honeydew dripping from canopy; sooty mold on leaves and surfaces below; weakens young trees Horticultural oil spray in late winter targeting overwintering females; systemic imidacloprid for persistent infestations