Leaf Spot and Powdery Mildew on Begonias
What would be causing my King Begonias leaves to get dead dried up spots on the leaves that soon grow to devour the whole leaf?
It sounds like your Begonia plant has either Bacterial leaf Spot disease or Powdery Mildew.
Bacterial Leaf Spot and Blight: When a plant gets Leaf Spot Disease, the attacking fungus or bacteria leaves small brown spots trimmed in yellow where it is feeding on the leaves. These spots may vary in shape, color, and size.
Powdery Mildew: There are several types of fungus that cause Powdery Mildew. The mildew appears on the surface of leaves and other parts of a plant as a powdery grayish-white substance. Grape Ivy, Begonias, and African Violets are prone to this disease. Powdery Mildew causes the tissue in the leaves under the fungus to die. This results in leaf-drop and a general decline in the growth of the plant.
With all fungal and bacterial diseases, better air circulation, well-drained soil, dry leaves, and less water help control Leaf Spot Disease and Powdery Mildew. Never mist a plant with either of these plant problems. You can use a commercial Fungicide or the homemade remedy of putting a tablespoon or two of baking soda and a teaspoon or two of mineral oil in a spray bottle of water. Shake the solution well and then spray all areas of the plant that are infected. Keep infected plants away from your other houseplants.