Rose leaf diseases: Powdery mildew
A very common disease and the good thing is that it causes minor damage to your rose plants.
Many plants can get powdery mildew and roses are no exception. Always new, fresh growth is targeted.
Identification:
Powdery mildew comes from the Erysiphales group of fungi and we can easily recognize it. New leafs and buds are covered with a white powdery agent. It looks like confectioner's sugar being dusted onto the rose. In severe cases the leafs curl up, dry out and buds don't open anymore
Causes:
99% of powdery mildew is caused by damp, warm weather with high humidity and with very dry conditions and bad air circulation.
Cure:
Choose resistant, modern new varieties. Don't use Chemical fertilizer which is high in nitrogen, so a low N(PK). Only use organic based fertilizer with NPK around 6-7-9
High nitrogen fertilizer causes weak, soft growth which is extreme susceptible to mildew
Especially with climbing roses it's essential to make sure she has a good air circulation so don't plant on a very secluded spot without good air flow. Make sure your trellis or wires aren't attached too close against the wall. Let the air flow behind it.
For shrub roses: Don't plant roses in very hot, dry spots with no air flow
Use Neem oil to treat severe infections. You'll see results within three days. I don't think there's anything better than NEEM oil for this problem. It works immediately. Repeat the treatment after five days. Make sure to spray the Neem solution all over the rose canes and foliage, also the back side of the foliage. Try to avoid spraying on flowers. Closed buds can be sprayed. Once the mildew turns grayish/black it means it's dead and the plant is cured.
While it isn't beautiful powdery mildew isn't a big problem and your rose usually will recover on her own.
Climbers Susceptible to mildew are Zepherine Drouhin and Paul's Himalayan musk rambler so don't plant them in very dry, hot locations with low air circulation. Preventing is better than curing.
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