Clark County logo   Clark County Washington title  
Links to finding county services
Search the Web site
 
Clark County home page A to Z index Find it Links to other sites News releases Contact us

Environmental Services

Recycling, Garbage & Hazardous Waste

Waste Reduction

Community Share Fair

Garbage Collection & Disposal

Recycling Collection & Disposal

Recycling A-Z Index

Solid Waste Advisory Commission

Household Hazardous Waste (HHW)

Small Quantity Generators (SQG)

Yard Debris/Composting

School Programs

Naturally Beautiful
Backyards

News

Calendar

Publications

Documents


Recycle A to Z

alternatives to pesticides - plant disease - black spot

black spot

Black Spot

Black spot is a fungus common to rose bushes. Symptoms appear as coal-black lesions on upper and lower surfaces of leaves. Heavily diseased leaves tend to turn yellow and drop prematurely. When excessive premature defoliation occurs, the plant forms a new set of leaves, which causes a considerable drain on food reserves in the roots. This results in a weakened plant with poorly matured wood. A few days after the spots first appear, little black pimples show up in the spots; this signals that the spores are about to be discharged and you should act fast to remove and discard those leaves. Spores are carried by air currents, insects, tools, hands and clothing.

Prevention
When selecting a rose bush to buy, consult a knowledgeable nursery person or the WSU Extension agent or Master Gardeners for varieties that are less prone to black spot. Some varieties are more susceptible than others.

Physical control
Remove infected leaves from the bush and those already fallen on the ground so they can’t re-infect the plant. Prune away excess foliage and sickly canes to improve air circulation. In the spring, remove the mulch around the base of the plant and rake the ground thoroughly to expose it to the sun. When new shoots appear, apply generous amounts of new mulch. Never water roses from overhead. Keep the foliage as dry as possible because dry leaves won’t support the fungus.

Least-toxic chemical control
Dust with a finely ground sulfur when temperatures are under 85 degrees. It tends to burn leaves if applied in very hot weather.

Back to A-Z list