Question
I have two crepe myrtles in backyard with severe powdery mildew.  They are a number of years old and this is the first year that they have not bloomed.  I treated them with fungicide several times but they did not seem to get better.  I cut them both back yesterday to get rid of all the sick branches.  Should I continue to treat them?  Now I'm worried that perhaps I shouldn't have cut all the foliage back. What do you think?

Answer
Powdery mildew has been more common this season because of dry weather, warm days and cool nights -- conditions which favor development of this disease. If powdery mildew is showing up in your crape myrtle landscape planting what should be done about it? If infection isn't excessive, infected twigs may simply be removed by pruning. Heavily powdery mildew infected plants will probably require fungicide treatment for full recovery.

Homeowners who have had severe crape myrtle powdery mildew problems in past seasons should start fungicide application immediately after the first sign of the disease. It may be necessary to continue fungicide sprays until leaves are mature, at which time they are less susceptible to the powdery mildew fungus. Also, fungicide applications can be made during the flowering period to prevent blossom blight infection.

Although several fungicides help reduce crape myrtle powdery mildew, the most effective products are Spectracide Immunex or Immunox. Apply Immunex (1 ?fl. oz. per gallon of water# every 21 days or Immunox #2 fl. oz. per gallon of water every 14 days) until disease control is obtained. These fungicides may also be used for the control of powdery mildew, and other diseases, on roses, dogwoods, as well as other ornamental plants.  

It can be controlled with a fungicide spray but the spray should be repeated every ten days or so for three applications. Here is a web link that will give information on powdery mildew and the fungicides recommended. Check with your local nursery/garden type store and ask for a fungicide for powdery mildew.


Cutting all the foliage back is not a good thing. It did nothing for the mildew. The good thing it should recover.

The ideal crepe myrtle pruning time is either in the late winter or early spring when the tree is in its dormancy. In your area I would say early March.   This is the best time to prune if you are reshaping the tree, removing deep or weak branches, trying to encourage new growth or size maintenance.

Before going into how to prune crepe myrtle trees, we need to look at if you need to prune you crepe myrtle at all.

While pruning crepe myrtle trees is good for helping to keep the tree shaped like you would like it to be, it is not normally necessary to the health of the tree. Prune crepe myrtle trees when you wish to shape them or if you find the branches are too close together for your taste, but for the most part, you do not need to prune crepe myrtle trees.

There are two schools of thought when it comes to pruning crepe myrtle trees. One is a natural style and the other is a formal style.

Natural style
A natural style of pruning will mostly address the limbs within the tree that may be keeping your crepe myrtle tree from putting on the best show it can. Things like inward growing branches, damaged branches, branches that are too close together or rubbing against each other and other minor issues that could affect the canopy of the tree. Smaller inside branches may also be removed to open up the space inside the tree. With a natural style of pruning crepe myrtle trees, main branches will be left alone to promote thick sturdy trunks.

Formal Style
With a formal style, when you prune crepe myrtle trees, you are pruning for outward shape rather than inner openness. Formal style pruning is also thought to encourage additional blooming since it forces the tree to grow more new wood, which is where blossoms are formed. In a formal style, the decision on how to prune a crepe myrtle tree is based on how high and how wide you would like the tree to be. All branches outside the chosen dimension is cut off, much like you would trim a hedge. This style of pruning can keep crepe myrtle trees in the same landscape setting uniform in size and shape and lends a more formal look to them.

Here is a web link to more information on pruning crept myrtle
http://www.clemson.edu/extension/hgic/plants/landscape/trees/hgic1009.html



http://ohioline.osu.edu/hyg-fact/3000/3047.html