powdery mildew

Asked October 24, 2015, 12:07 PM EDT

We have 4 peony plants that seem to do fine in partial sun, but in the last few years I have been getting powdery mildew on them in the later part of the season and also on the crape myrtle bushes. What can be done to alleviate this problem. I normally cut the plants down and put them in the yard waste and d9 not shred them for compost. We live in Ferndale, MD next to the Airport. Thank you. Sincerely,

Anne Arundel County Maryland

1 Response

Powdery mildew has become a bigger problem on peonies the past few years. Make sure there is adequate sunlight and good air circulation to reduce humidity levels. Allow proper plant spacing for the same reasons. Pruning for better air circulation also may help. Practice good sanitation. Since the powdery mildew does not show up until late in the season it may be best to tolerate it.

Cut down all infected foliage this fall as soon as frost turns it brown (or before if the mildew has killed it.) Get rid of this infectious material. Next spring, monitor your peonies, and as soon as you see one infected leaf, pull it off. You will have to decide it you want to spray a fungicide or a horticultural oil labeled for powdery mildew or tolerate it. Fungicides are preventative--not curative. They will halt further infection, but cannot restore infected leaves to health. Here is our website info on powdery mildew: http://extension.umd.edu/hgic/powdery-mildew-annuals-bulbs-groundcover-perennials-and-vines

Crape myrtle - See our website for more information on trees and shrubs. http://extension.umd.edu/hgic/powdery-mildew-trees-and-shrubs

This fungal disease is usually not lethal to crape myrtles but is certainly not attractive. Control begins by selecting powdery mildew resistant varieties. Place susceptible plants where there is adequate sunlight and good air circulation to reduce humidity levels. Allow proper plant spacing for the same reasons. Pruning for better air circulation also may help.

If severe, you can spray as soon as you notice the mildew next season. Check the label registration on fungicides and horticultural oil products for powdery mildew control listings. However, this disease will not kill the plant and you do not have to spray.
Next season you will have to decide if you want to spray. Fungicide treatments can help to protect new or un-infected foliage they are not curatives. http://extension.umd.edu/hgic/powdery-mildew-trees-and-shrubs
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