Powdery Mildew

(November 2012)

I have a fungus of some sorts growing all over my zinnias.  I'm not sure what it is or what to do about it. I figured that because Zinnia season is over with I may as well just let them die but I do not know if this white spotty fungus or mold disease will spread to other parts of the garden or come back next year with a vengeance. What do you suggest?

Zinnias are often plagued by powdery mildew.  The best thing you can do is to clean up the garden, disposing of all the plant remains. You should also remove the underlying mulch so you can start the season off clean.  Pay attention next summer, and control if needed if it begins early in the season. Many of the new varieties of zinnias are resistant to powdery mildew.

 (June 2008

I found some silvery stuff on the end of the leaves of my crepe myrtle.  The others are blooming right now, but this plant is not.  What should I do?  Prune off the bad leaves and branches or spray it with something or use some kind of systemic stuff?

It sounds like you have powdery mildew on your crape myrtle, a common fungal disease.  Some varieties are more susceptible to it than others.  If you have a heavy infestation on the tips, try pruning it back, but not by much or you may delay blooming even longer.  Use a broad spectrum fungicide such as Daconil, Funginex or Immunox.  Spray once, wait two weeks and spray again. Then see what happens. It is often difficult to get a handle on the disease once it kicks in for the season.  Make sure when pruning your crape myrtle next year that you try to keep the center as open as possible to allow for better air circulation and sunlight input.

(September 2007)

I have a few young crepe myrtles planted along the south side of the house.  They are about 2 years old, now.  I believe they contracted "powdery mildew". I checked the extension website and used a systemic treatment on them per the website.  The powdery mildew seemed to slow down, but it did not go away.  What should I do now?  Will it come back next spring?  My sister said she thought I should cut off all the mildewy looking limbs and leaves now.

This late in the year, I wouldn't do any more spraying or pruning.  The key is good sanitation.  As the leaves fall, rake and destroy them, but you don’t need to prune out the branches.   Some varieties of crape myrtles get powdery mildew every year, and others rarely have it. If you have a variety that is highly susceptible, consider a preventative fungicide application next spring, before you see the disease.  Also, prune the plant to make sure that the branches are spreading out with good air circulation and sunlight penetration.  Folks who severely cut their crape myrtles back every year end up with an excessive amount of foliage which cuts back on air circulation and can make the disease worse.

(July 2007)

I have a white dogwood tree that is about three years old.  It has not grown much and never flowered.  This year the new leaves are starting to curl and have a white substance on them.  It is getting plenty of water, in fact, maybe too much with the rain that we are having.  It is planted in the shade of two giant oak trees.  Is this something I need to worry about...what do I need to do to stop whatever this is and  how do I prevent this problem in the future?

Your tree is too young to bloom, so simply give it time for that.  The curling leaves and white substance are caused by powdery mildew, a common fungal disease.  Overhead watering (i.e. rainfall too,) coupled with high humidity is the culprit.  When you water, try to keep the foliage dry, or at least water early enough in the day that moisture doesn't remain on the foliage overnight.  There are fungicides that can help, but it is difficult to get a handle on once it starts for that season.  If the tree is in heavy shade, it may never bloom, and that can also reduce air circulation making the powdery mildew worse.  This has also proven to be a good year for powdery mildew on a variety of plants.  Sprays will give limited help this year.  If the problem becomes an annual one, then preventative sprays would be called for.  For more information on powdery mildew get a copy of our fact sheet 6113, which you can read on line at www.uaex.uada.edu or get a copy from your local county extension office.