Powdery Mildew is a common and easily recognized plant disease caused by a fungus. Fruits, vegetable, flowers and even grasses can be affected. Lilacs, bee balm, phlox, zinnias, and roses are some flowers that can be affected by powdery mildew.
Unlike other diseases that require rainfall, powdery mildew will spread quickly during warm, dry days and cool humid nights. Under favourable conditions, the spores are released and spread by wind or insects.
Powdery mildew will cause leaves to develop small white spots on the surface, which over time, will develop into white or gray powdery patches. The lower leaves are usually the most affected. Infected leaves will often drop prematurely. Powdery mildew can also affect the stems, flowers, buds and even the fruit.
While powdery mildew isn’t something we would like to see on any of our plants, it is not a fatal disease and the plants will not die. However, the disease can cause stress in the plant, weakening it over time.
Tips to Prevent and Manage Powdery Mildew:
- Prevention is the best way to avoid powdery mildew. Choose healthy, disease-resistant plants.
- Overcrowded plants are more prone to disease. Pruning and thinning out the plants will improve the air circulation.
- Avoid overhead watering, as this will increase the humidity.
- Avoid over fertilizing the plant, as the new growth will be susceptible to the disease.
- The fungus needs live tissue to survive. To manage the disease and prevent new growth, immediately remove infected leaves, stems and branches.
- To treat or prevent powdery mildew, many home gardeners apply a spray made of diluted milk onto the plant. Mix 1 part milk with 9 parts water and spray the stems and tops of leaves with the solution. Reapply after rain.For the best results, repeat applications are required. Milk has been proven to be as effective as commercial fungicides.
- Another solution is to spray leaves with a baking soda mixture (1 tsp in 1L water). This solution is known to raise the PH level, which makes makes the environment less suitable for the spores to multiply. Repeat application as necessary.
- Plant Diseases: Black Spot on Roses (funflowerfacts.com)
- Plant Pests and Diseases (growerdirect.com)