What Diseases Turn Shrubs Brown?

Powdery Mildew

• Powdery mildew, caused by any of a number of different species of fungi, can infect a wide variety of ornamental shrubs, including azaleas and lilacs, as well as several varieties of trees. It first appears as a powdery substance on the surface of leaves, and more severe infections cause browning of leaves, leading to early defoliation and general unsightliness. A number of cultural controls can be implemented, including planting plants at appropriate spaces, maintaining high vigor in your plants and regular watering. A variety of fungicides is also available.

Verticilium Wilt

• This shrub disease infects hundreds of species, although it typically infects azaleas, viburnums and Japanese barberries. The symptoms, which include yellowing and browning of leaves, defoliation and leaf die-back, frequently occur in the months of July and August. There are a number of preventative measures you can take, including planting seedlings in moderately fertile soil that contains higher levels of potassium and less nitrogen and watering plants generously. Fungicides are generally not effective, and you should take a laboratory test to verify that your plant is infected with the wilt.

Cylindrocladium Blight

• This shrub disease typically infests both azaleas and rhododendrons, and symptoms usually appear quickly. The leaves turn brown or black and fall within three or four days. Other symptoms include brown spots on the stems of the plant with white spores on the spots. Plants typically die quickly after infection. Control involves raking and destroying fallen leaves to reduce the spread of the disease, using disinfected tools at all times and, in the worse infections, removing the affected plants. You can also use chemicals such as thiophanate methyl and triflumizole.

Botryosphaeria Canker

• Botryosphaeria canker, caused by a pathogen of the same name, affects liburnums, causing the leaves of the plant to wilt and die. The branches then become infected with dark brown or black fungal structures and eventually die back, while the wood itself turns dark brown. The disease typically occurs among shrubs that have been stressed due to drought conditions, so keep plants thoroughly irrigated to prevent outbreaks. You should also prune affected branches in order to keep the disease from spreading to other branches and shrubs.