POWDERY MILDEW IS A FUNGUS
Powdery mildew is a fungus that looks like a powdery coating over the leaves, spots or patches of white to grayish, talcum-powder-like growth. The disease is most commonly observed on the upper sides of the leaves. It also affects the bottom sides of leaves, young stems, buds, and flowers and young fruit. Infected leaves may become distorted, turn yellow with small patches of green, and fall prematurely. Infected buds may fail to open.
HOW TO CONTROL POWDERY MILDEW ON PLANTS
· First step is to remove and discard infected leaves and other parts to help cut down on the spread. (Don't put them in your compost, as temperatures may not be hot enough to kill the fungus)
· Avoid overhead watering. The roots need the water most.
· Avoid watering at night, especially in spring when moisture will not evaporate due to cool nights. (Humidity increases spore germination) Spray infected plants every 7 to 10 days with an earth-friendly fungicide.
· Selectively prune overcrowded plant material to help increase air circulation. This helps reduce relative humidity and infection.
· Avoid late-summer applications of nitrogen fertilizer to limit the production of succulent tissue, which is more susceptible to infection.
THE CURE-ALL REMEDY FOR POWDERY MILDEW ON PLANTS
I recommend first spraying with a diluted solution of baking soda and dishwashing soap. Mix one tablespoon of baking and one teaspoon of liquid soap (not detergent) to a gallon of water. Spray on plants every one to two weeks.
My secondary option is to use Neem oil or Potassium bicarbonate, as they are both organic options. Some people actual combine the two. Mix one tablespoon of baking soda with a teaspoon of dormant oil and one teaspoon of insecticidal or liquid soap (not detergent) to a gallon of water. Spray on plants every one to two weeks.
Some gardeners are fond of using a 5% cider vinegar solution or 5% generic, ethanol based mouthwash. If cultural controls fail to prevent disease buildup or if the disease pressure is too great, an application of a fungicide may be necessary.
**For future purchases, try to purchase plant cultivars (roses, tomatoes, etc.), which are more disease resistant or tolerant of powdery mildew. A little bit of initial research goes a long way in minimizing long-term plant care.