What's eating my quercus robur 'fastigiata'?

Quercus robur 'Fastigiata' (fastigiate English oak) hosts a rich community of insects, most harmlessly. Oak processionary moth caterpillars are a significant pest in southern England and Europe. Knopper gall wasp deforms acorns. Aphids and leaf-feeding caterpillars are common. Oak processionary moth is the most serious threat due to its toxic hairs and defoliation potential.

Processions of hairy caterpillars defoliate shoots from April–June; urticating hairs cause severe skin, eye, and respiratory irritation in humans and animals — a public health concern. Report to local authority or Forestry Commission (UK); professional removal of nests required; do not touch caterpillars or nests; Bt spray by licensed operators in early spring.

Leaves in the compact upright crown holed or entirely consumed in spring flushes; repeated defoliation weakens the tree over years. Grease bands on trunk in October; Bt or pyrethroid spray at bud burst on young trees; tolerate on large healthy specimens.

Acorns deformed into ridged, sticky green or brown galls rather than developing normally; heavy years can eliminate the entire acorn crop. No practical control; purely cosmetic / ecological impact; remove galled acorns to reduce local wasp populations marginally.

Colonies on leaf undersides cause honeydew drip and sooty mold; large populations can distort new growth in spring. Natural predators (ladybirds, lacewing larvae, parasitic wasps) usually control populations without intervention; insecticidal soap for persistent infestations on young trees.