Rhododendron leafhopper and bud blast

Rhododendron leafhopper causes little direct damage but is a problem as is thought to spread a fungal disease known as bud blast which kills flower buds.

Bud blast on rhododendron flower buds

Quick facts

Common name Rhododendron leafhopper
Scientific name Graphocephala fennahi
Plants affected Rhododendron
Main cause A sap-sucking insect that may facilitate the spread of bud blast disease
Timing July-October

What rhododendron leafhopper and bud blast?

Rhododendron leafhopper is a sap-sucking insect that is active on rhododendrons from late spring to autumn but is most noticeable when the brightly coloured 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. They 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 flowers buds in late summer-autumn. A fungal diseases, known as bud blast (Pycnostysanus azaleae), is thought to 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-chemical control

There are no easy non-chemical measures for the leafhopper. However, flower buds infected with bud blast should 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.

Chemical control

Rhododendron leafhopper numbers can be reduced by spraying rhododendrons with contact insecticides, such as deltamethrin (e.g. Bayer Sprayday Greenfly Killer), lambda-cyhalothrin (e.g. Westland Resolva Bug Killer), or a systemic spray such as thiacloprid (e.g. Bayer Provado Ultimate Bug Killer) or acetamiprid (e.g. Bug Clear Ultra). 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. Plants in flower should not be sprayed due to the danger to pollinating insects.

There are no effective fungicides for bud blast.

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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. 

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