Powdery Mildew is caused by the Oidium fungus which thrives under conditions of high humidity and poor air circulation, especially after sudden changes in temperature. Such conditions often occur in spring when precipitation is high, and hot days alternate with cold nights. Powdery Mildew grows superficially on the leaves and flowers of African Violets, covering them with a light gray powder. If left untreated, Powdery Mildew will cause discoloration of the affected leaves and flowers. Eventually, the affected parts of your African Violet will begin to wither and die.
If your African Violet exhibits these symptoms, it probably has Powdery Mildew. (Note: Do not confuse the light gray powder of Powdery Mildew with the fuzzy gray mold of Botrytis. While Powdery Mildew may not affect the entire plant, those areas which are affected will be uniformly covered by the fine gray powder. The Botrytis fungus, on the other hand, has a fuzzy appearance and is typically spotty in distribution.)
First, isolate all affected plants in order to prevent the Powdery Mildew from spreading. Next, remove all dead or dying tissue from the affected plants. Space plants to increase air circulation. Reduce humidity to no more than 60 percent, and maintain a warm, constant temperature that varies no more than 10 degrees.
If you do not see improvement after two days, try spraying Lysol on the affected areas. When lightly sprayed, Lysol may cause some discoloration of the flowers, but it should not damage the leaves. Lysol is also much less expensive than other, chemical solutions. However, if you still do not see improvement after two more days, you will need to treat with a fungicide such as Benomyl or Captan (as directed on the label).
As an alternative to traditional chemical treatments, try dusting with sulfur or spraying with a baking soda solution (about 1 teaspoon per quart of water).
Always remove spent flowers and leaves as you see them. Maintain good air circulation between your plants, especially where the air is damp and still. Be particularly watchful during the spring when precipitation is high and temperatures vary between extremes. Keep your growing area and tools clean. Before repotting, disinfect pots with a 10 percent bleach solution, i.e., 1 part bleach to 9 parts water. If Powdery Mildew is recurring problem, you may want to try placing small containers of sulfur among your plants.
Important Note on the Use of Pesticides
Please note that almost all pesticides are formulated for specific uses and conditions. When applied incorrectly, pesticides can cause ill health or damage to plants. Therefore, when using any kind of pesticide or chemical treatment, always apply as indicated on the product label.
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