Rhizoctonia is a fungus which attacks the leaves and petioles of African Violets. The fungus thrives in moist conditions, especially when the leaves are wet. Symptoms will typically first appear on the lower leaves, then move upward. The most distinct symptom is the oval or peanut-shaped spots which Rhizoctonia produces on the leaves. These spots exhibit a distinct outline, but are often mottled within. Spots will vary in size though usually no larger than 1/4 inch. If left untreated, Rhizoctonia will eventually spread to all the leaves. If this happens, Rhizoctonia will be fatal.
If your Violet has this symptom, it probably has Rhizoctonia. However, before pursuing treatment, it is important to distinguish Rhizoctonia from other conditions which may cause leaf spots. Specifically, it is recommended that you examine the other possible causes of brown or yellow leaf spots (see below).
First, isolate all infected plants.
Next, if Rhizoctonia is still in its early stages, the best remedy is to simply remove the affected leaves. This will generally stop the spread of the fungus. Thereafter, keep plants isolated for two weeks in order to insure that the fungus has been eradicated. In the meantime, increase air circulation for all your Violets and avoid getting water on the leaves. If you have not done so already, considering using a watering device which allows you to water from the bottom.
If the fungus is widespread or appears to be in an advanced stage, you will probably need to treat with Benomyl (as directed on the label).
Always maintain good air circulation between your Violets, and keep leaves dry. If possible, use a self-watering device which allows you to water from the bottom.
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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