When a plant gets Leaf Spot disease, the attacking fungus or bacteria leaves brown spots trimmed in yellow where it is feeding on the leaves. These spots may vary in shape, color, and size.  As with all other fungal and bacterial diseases, better air circulation, well-drained soil, dry leaves, and less water help control Leaf Spot disease on plants. Never mist a plant if Leaf Spot is suspected. You can use a commercial fungicide to treat the problem 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.