What's eating my tree rhododendron?

Tree rhododendron shares the pest complex of all outdoor rhododendrons: rhododendron lace bug, vine weevil, and rhododendron leafhopper are the main threats. Its larger size makes complete defoliation unlikely but infestations still weaken flowering and overall vigour. Partial shade siting greatly reduces lace bug pressure.

Stippled, pale-yellow bleaching on the upper leaf surface with dark sticky excrement spots on the undersides. Most damaging on plants in full sun. Spray leaf undersides with insecticidal soap, neem oil, or pyrethroid in late spring and repeat in summer. Systemic soil drench (imidacloprid) gives longer protection. Siting in dappled shade greatly reduces attack.

Distinctive notched, scalloped edges on leaves caused by nocturnal adult feeding. Grubs eat roots and can kill pot-grown specimens. Inspect at night with a torch and hand-pick adults into soapy water. Apply pyrethroid to foliage when notching starts. Use nematodes (Heterorhabditis spp.) in moist soil in late summer against larvae.

Adults cause minor feeding damage but their egg-laying punctures into flower buds allow the bud blast fungus (Seifertia azaleae) to enter, turning buds brown and papery. Spray adults from late July to October with a contact insecticide (pyrethroid or thiacloprid where permitted) to reduce egg-laying. Remove and dispose of blasted buds to limit fungal spread.