Powdery mildew is a common fungal disease that commonly affects Roses but also affects other plants. Often happning in the early summer when the days are hot and the nights are cool, identifying Powdery Mildew is easy. It shows up as a light white/grey powder on the infected leaves and will slowly spread until it is covers most of the plant. Powdery Mildew is not only unsightly by causing withered yellowed leaves but eventually causes weakning of the plants. Weak plants grow slower and bloom less so helping prevent and/or treat Powdery Mildew is important.
Powdery mildew thrives in warm, dry climates; however, it also needs fairly high humidity — like the warm days and cool nights in late spring to early summer. Not enough sunlight and poor air circulation also contribute to conditions that encourage powdery mildew.
Although rarely fatal, if left unchecked it can eventually cause serious harm to your plants by robbing it of water and nutrients. Most infections cause minor damage such as leaves turning yellow or becoming withered or distorted, but plants can also become weak, bloom less, and grow slower.
Here are steps you can take to help prevent Powdery Mildew:
- Prune out canes on the interior of the plant that cross each other Read more about pruning Roses here.
- Space Roses about 3 feet apart and keep a few feet away from walls / fences to allow adequate ventilation.
- Give your rose 6-8 hours of sunlight
- Remove dead/diseased foliage if it appears
- Preventatively treat with with a fungicide such as, .
An ounce of prevention is worth a pound of cure as they say. Market products are geared more towards prevention than treatment. Spray treatments liberally making sure to saturate tops and bottom sof leaves as well as any other affect areas. It may take multiple applications for complete treatment. Apply once a week for three to four weeks, then wait to see results. Reapply as needed.
- Baking soda solution: Mix 1 tablespoon baking soda and ½ teaspoon liquid soap such as Castile soap (not detergent soap) in 1 gallon of water.
- Neem oil: Neem oil is mildly effective by itself but can be added to the baking soda solution to make it more effective. Make sure to not spray neem oil before or during the hottest period of the day as it can encourage leaf burn.
- Powdery mildew fungicide: Use sulfur-containing fungicides like, , as both preventive and treatment for existing infections.
While Powdery Mildew is more commonly found on Roses, there really isn’t a plant that it can’t affect. BUT some plants are more likely to be susceptible than others such as:
And don’t forget – when pruning plants will powdery mildew – santize your pruners to prevent spreading it to other plants!