Powdery Mildew

What is powdery mildew? This fungus disease affects a wide variety of plants, including lilacs, phlox, roses, squash, beans, and peas. It takes away a plant's nutrients, which causes the plant to bloom less and become weaker. In some cases, if the infection is severe enough, powdery mildew can kill your plants. 

How to Identify Powdery Mildew

Plants infected with powdery mildew look as if they have been dusted with flour. It usually starts off as circular, powdery white spots. It usually covers the upper part of the leaves and affects the older leaves first; the leaves turn yellow and dry out. The leaves, buds, and growing tips will become distorted as well. These symptoms usually appear late in the growing season. 

How to Control Powdery Mildew 

• Rubbing the infected leaves together can help partially remove the disease from your plants.
• Remove all the infected plant parts and destroy them. Remember, do not compost any infected plant, as the disease can still be spread by the wind.
• Spray infected plants with fungicides. Effective fungicides include sulfur, lime-sulfur, neem oil, and potassium bicarbonate.

Prevention

• Plant plants that are resistant or tolerant to powdery mildew.
• Powdery mildew thrives in hot and humid weather, so avoid overhead watering to reduce humidity. Also selectively prune overcrowded areas to increase air circulation; this also helps reduce humidity for your plants.
• Spray your plants with fungicides according to their directions. If you don't want to use fungicides, try spraying your plants with a solution of 1 teaspoon baking soda in 1 quart of water. Remember to spray your plants thoroughly.