The Q&A Archives: Zinnias

Question: I love zinnias but they always get moldy (white fuzzy) Is there anything I can do to prevent this?

Answer: Many zinnias are susceptible to a fungal disease called powdery mildew. Powdery mildew appears as a whitish/greyish powder on foliage. It overwinters on living plants, and can be difficult to eradicate. If the zinnia plants begin to decline rapidly, you may want to simply remove them. It's unlikely you'll be able to control the disease in time for these heat-loving plants to recover and put out more flowers before cool weather sets in. There are some things you can do to minimize its effects next season. The first line of defense is to grow resistant varieties. Also, be sure to space plants properly for good air circulation, and thoroughly clean up plant debris at the end of the season. Powdery mildew is unique among common plant diseases in that it doesn't require a wet leaf surface to spread. It can thus thrive during hot, dry weather, which is why you see it appearing late in the growing season. The general advice to inhibit the spread of fungal diseases is to avoid wetting leaf surfaces. In the case of powdery mildew, you can actually inhibit infection with frequent sprays of water. Also, examine plants frequently, removing any affected foliage immediately.

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