Rhododendron bud Blast is a fungal disease of Rhododendrons and Azaleas, affecting the tight dormant flower buds. The disease if more noticeable in the spring, when buds will be dark brown and normally covered in small black hair-like growths of the fungus disease. It causes brown buds to form on the plants of either Rhododendrons or Azaleas. The brown flower buds do not open.
The affected Rhododendron or Azalea buds will be firm to the touch, unlike those brown buds which are sometimes associated with either severe frost damage, or lack of water in important July-September growing months of the previous year.
The brown buds on Rhododendrons and Azaleas caused by the bud Blast fungus are beyond cure.
Image ©Cheryl Moorehead
They should be picked off and destroyed as soon as found, for the fungus spores can live on the dead bud for up to three years. Any insect visiting the infected bud is then a potential carrier for the disease to other healthy buds.
The fungus spores are thought to be carried by the Rhododendron Leaf Hopper, which lays its eggs in the Rhododendron and Azalea buds in late summer. The entry point is then open for the spores to enter, or possible be carried in during the egg laying process.
The spores of Rhododendron Bud Blast Fungus are also carried by wind. This seemingly being a prime source of the spread in autumn as the spores are ripe, and the winds are stronger. If you live in a 'Rhododendon' area, it may be as well to alert those gardeners in the vicinity, in order to carry out a concerted 'cleaning' of the area.
Rhododendron Leaf Hoppers are active during late summer and early autumn. If they are present, then a contact spray of Bifenthrin, or a systemic spray of Provado should be applied. Other pests may also cause enough damage for the fungus spores to enter, so routing spraying is a good idea where there are problems with Bud Blast.
Any brown or otherwise discoloured buds should be removed as a matter of routine and burned. These should be remove at first sight for whatever reason the browning has occured.
Rhododendron Bud Blast was at one time confined to SE England, but cases have been recorded outside this area in recent years. Possibly as a result of the milder winters.