Crape myrtle trees yellowing in FL - in August?

I have several crape myrlte trees which were planted in late March.
They have been doing great, putting on much growth for young plants and blooming with colors as expected all summer.
Now, in mid-August, several have some yellow leaves. One has quite a few and almost no colored blooms left.
What is likely to cause these yellowing leaves? I did a search and found no mention of yellow leaves on crape myrtles aside from the change of color in the fall.
There have been a number of ants running up and down the branches. When I checked the trees after seeing the yellow leaves, there seem to be more than usual. I'm not sure if this is the cause. I also don't know what kind of ants they might be; they seem somewhat small for fire ants.
I've ensured the trees have a lot of water several times a week. There still is time-release fertilizer on the ground from my last application a couple months ago. The soil is mostly sandy and I live in Orlando, FL. The trees get full sun much of the day. It's been in the lower-mid 90s and high humidity for at least 2 months.
Do I need even MORE water? Do I need some added fertlizer? If so, what kind? Do I need to cut back on the water? Do I need to kill the ants? If so, how?
Any information on yellowing of crape myrtles in August in FL would be useful.
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On Mon, 15 Aug 2005 21:14:38 -0400, "Apropos"
As usual a simple google search of " crape myrtle yellow florida" will garner lots of solid information.....
http://edis.ifas.ufl.edu/pdffiles/MG/MG26600.pdf
Google is your friend .....:>)
http://www.ncan.com/nursery%20notes%20articles%202003/Yellow%20AlertNN.pdf
Acts of creation are ordinarily reserved for gods and poets. To plant a pine, one need only own a shovel. -- Aldo Leopold
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Crape Myrtle will do well on normal rainfall without additional irrigation. One possible reason for the yellowing could be too much water. Orlando was about 25 inches above normal rainfall just for May and June (!), and you've had thunderstorms almost every afternoon in July and August. You don't need irrigation, and hopefully your plants are located where the site drains satisfactorily before the next storm comes by. Suggest you cut back or eliminate the irrigation. I have not seen ants to be a problem for crape myrtles - they're just everywhere in Florida.
Crape Myrtle are extremely hardy -- suggest you just follow good horticultural procedures. At least 3-4 inches of good mulch (except right next to the trunk), well drained location, stop the overwatering. Don't overfertilize, but in Florida expect that time release fertilizer will have been used up within 60-90 days max. It's better to use smaller amounts, more frequently, especially with young plants. The University of Florida IFAS has a good website on crape myrtle at http://hort.ifas.ufl.edu/gt/crapemyrtle/crapemyrtle.htm , and your county extension service has a brochure on growing crape myrtles.
Two other factors with crape myrtle that affect plant health but may be too late for you to implement -- (1) Try to plant crape myrtle where there is adequate airflow (ie, not next to a wall or in a corner with no ventilation) to avoid powdery mildew problems, and (2) IMHO the best cultivars are the series of releases with American Indian tribe names -- they do very well in Florida and are mildew-resistant.
Regards --
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