“Please give me advice on the prevention of black spot before it occurs.” Question from Carol of Drums, Pennsylvania
Answer: Black spot (Diplocarpon rosae) is such an annoying fungal disease of roses. Here are six measures to help prevent it:
1. Clean your bushes in fall and winter. Remove all fallen leaves and any dead branches from your rose bushes. The fungus overwinters on dead, infected plant material.
2. Apply a dormant oil spray before roses leaf out in spring. Dormant oil sprays deter fungal diseases existing on the plant. (Click here to learn more about horticultural oil sprays.)
3. Prune roses to promote aeration. Moisture on the leaves helps fungal diseases, like black spot, take hold. (That’s why roses grown in dry climates have fewer disease problems.) Prune off extra branches and sprouts to open up plants and help prevent black spot. (Click here to learn more about how to prune roses.)
4. Space roses to promote aeration. Space your roses according to nursery recommendations. Overcrowding can encourage foliar moisture and subsequent fungal problems.
5. Plant roses in full sun. When you plant roses in full sun, their foliage dries faster, which creates a less favorable environment for black spot to proliferate.
6. Water roses from the bottom. Bottom water your roses to help keep their leaves dry.
I hope that these tips help!
Happy rose growing,
Black Gold Horticulturist