The leafhoppers are a family (Cicadellidae) of

Sap is a fluid that circulates through a plant's vascular system, in a similar way to blood moving through our veins. Phloem sap carries the sugars produced in the leaves by photosynthesis down to roots and other storage organs, as well as carrying minerals and hormones. Xylem sap is watery and transports nutrients absorbed by the roots upwards to the rest of the plant. Some plants leak sap from wounds or pruning cuts, and this is known as bleeding.

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

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 fungus, known as bud blast (Seifertia azalea), may infect the buds through the egg wounds, although some research has placed doubt on this assumption. Infected flower buds turn brown and die.

There are no simple control measures for rhododendron leafhopper. However, flower buds affected by 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.

When choosing control options you can minimise harm to non-target animals by using the methods in the non-pesticide section below. Pesticide treatments are likely to kill natural enemies and are only likely to be successful if the entire plant can be reached. 

Non-pesticide 

• Rhododendron leafhopper does not affect the growth or vigour of plants and so can be tolerated
• 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
• Encourage predators and other natural enemies of suckers, in the garden, such as birds, ladybirds, wasps and ground beetles

Pesticides

• There are no effective fungicides for bud blast
• In some gardens it is impractical and not desirable to attempt control with pesticides as leafhoppers will fly in from nearby gardens or from Rhododendron ponticum growing in woods
• Organic sprays, such as natural pyrethrum (e.g. Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear Fruit & Veg, Vitax Rose Guard) have a largely physical mode of action. These are broad spectrum so will kill a wide range of insects. These pesticides have a very short persistence and so may require reapplication to keep leafhopper numbers in check.  Plant oil and fatty acid products are less likely to affect larger insects
• Plant invigorators combine nutrients to stimulate plant growth with surfactants or fatty acids that have a physical mode of action against leafhoppers (e.g. Ecofective Bug Control, Growing Success Bug Stop, RoseClear 3 in 1 Action and SB Plant Invigorator). These products contain some synthetic ingredients and so are not considered organic
• Further information about the use of pesticides available for management of leafhoppers is available on the pesticides for gardeners leaflet

Inclusion of a pesticide product does not indicate a recommendation or endorsement by RHS Gardening Advice. It is a list of products currently available to the home gardener.

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

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 it was thought that flower buds became 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.