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