What are rhododendron leafhopper and bud blast?

There are several species of leafhopper that can be encountered by gardeners, they are sap sucking true bugs.

Rhododendron leafhopper only feeds on rhododendron. It is active on rhododendrons from late spring to autumn but is most noticeable when the brightly coloured bluish-green adults are present in late July-October.

Bud blast spoils developing flower buds, it is a fungal infection thought to be associated with the activities of the leafhopper.

Symptoms

The nymphs of rhododendron leafhopper are creamy white wingless insects that live on the underside of rhododendron leaves. The adults are 8-9mm long and have pale yellow heads with a bluish green thorax. The wings are folded back along the body and are bluish-green with two orange stripes. The adults often rest on the upper surface of the foliage in sunny weather but readily leap off when disturbed. White cast skins shed by the nymphs may be seen attached to the underside of leaves.

The feeding activities of the adults and nymphs have no obvious adverse effect on the appearance of the foliage or the plant's vigour. There would not be a problem if the females did not make egg incisions in next year's flower buds in late summer-autumn. A fungal disease, known as bud blast (Seifertia azalea), may infect the buds through the egg wounds, although some recent research has placed doubt on this assumption. Infected flower buds turn brown and die.

Control

Non-pesticide control

There are no easy non-pesticide measures for the leafhopper. However, flower buds infected with bud blast can be picked off and disposed of to reduce the amount of fungal spores being released in the vicinity of the plants. This may only be feasible on smaller plants.

Pesticide control

• Organic sprays, such as natural pyrethrum (e.g. Bug Clear Gun for Fruit & Veg, Ecofective Bug Killer), fatty acids (e.g. Solabiol Bug Free, Doff Greenfly & Blackfly Killer) or plant oils (e.g. Vitax Organic Pest & Disease Control, Bug Clear for Fruit and Veg) can give some control. These pesticides have a very short persistence and so may require reapplication to keep leafhoppers in check. Plant oil and fatty acid products are less likely to affect larger insects such as ladybird adults
• More persistent contact insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Westland Resolva Pest Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer) and cypermethrin (e.g. Py Bug Killer)
• The systemic neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra) is also available
• Follow label instructions when using pesticides
• Several applications may be needed during late summer-autumn to deal with adult leafhoppers flying in from nearby gardens or from Rhododendron ponticum growing in woods
• There are no effective fungicides for bud blast
• Plants in flower should not be sprayed due to the danger to pollinating insects
• Inclusion of a pesticide product does not indicate a recommendation or endorsement by the RHS. It is a list of products currently available to the home gardener

Download

Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)

Biology

Rhododendron leafhopper has one generation a year and it overwinters as eggs that are laid during late summer-autumn in developing flower buds. It is during the egg-laying period that flower buds probably become infected with bud blast. The eggs hatch in late April-May and the wingless nymphs feed by sucking sap from the underside of the leaves. The nymphs reach the adult stage in late July-August.