Powdery mildew is a common disease affecting many different houseplants, including jade plant, African violet, begonia, kalanchoe, and others. Powdery mildew appears as a white, dusty growth on the surfaces of leaves. The growth may appear in circular spots that coalesce or may cover the entire surface of the leaf. Severely affected leaves may be distorted.
Powdery mildew is favored by cool, moist conditions. Keeping plants away from cold air drafts and watering early in the day so foliage has time to dry off can help to prevent this disease. Plants should be kept in good vigor by avoiding drought stress. Plants should be inspected before purchasing. Severely diseased plants may need to be discarded. Several fungicides are available for use against powdery mildew, but most are not labeled for use on indoor houseplants.
Root and crown rots, caused by the fungi Phytophthora and Pythium as well as others, are another common disease that can affect nearly all indoor plants. The leaves of a plant with root rot may wilt, droop, or turn yellow. Rotted roots appear black or brown instead of healthy white, and often the outer root tissue easily strips off from the root, leaving the root core behind.
Root and crown rots are favored by warm, wet conditions. Plants undergoing other stresses are also more susceptible to root rots. Using potting mix with adequate drainage and aeration and maintaining optimal temperature, light, pH, moisture, and fertility will help to prevent root and crown rots. Avoiding overwatering is perhaps the most critical step to take to avoid root and crown rots.
Powdery mildew on greenhouse goldenrod and plantain.
This article originally appeared in the 2/11/2005 issue.