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Black Spot on Roses

Black spot is one of the most common diseases for roses. It is caused by the fungus Diplocarpon rosae.

Symptoms of Black Spot

Black spot appears as circular brown or dark gray spots surrounded by yellow tissue on rose foliage. In very severe cases, the spots can merge, discoloring the entire leaf. Close inspection of the spots will show the tiny spore-producing bodies. If left untreated early leaf fall and defoliation may occur.

Black spot occurs most frequently during rainy seasons when temperatures are moderate. Leaves on the bottom of the rose tend to become infected earlier because they are shaded by other parts of the plant and thus stay wet longer.

Black Spot on Roses
Black spot on roses

 

How to control and prevent black spot

Regular applications of Neem Oil, a botanical insecticide made from the seeds of the neem tree, can help control and prevent black spot. For prevention, apply on a 14 day schedule, if black spot is already present spary every 7 days.

Another option is to spray the roses with a mixture of baking soda and water (two tablespoons per gallon), however, roses will have to be sprayed weekly and after every heavy rain.