Question
I live in north Texas in the Dallas area.  I have 6-8 crepe myrtles (tree to bush size) on my small house property.  Only one of my tree size (it's 10-15 feet tall, and probably 7 years old# crepes has something wrong with it.  The symptoms include; white powdery 'stuff' all over the limbs.  #the leaves are not much affected#  Also, the tree has some sort of sticky liquid covering the limbs and leaves.  The limbs are almost all drooping to the ground.  
  We have had a very hot and dry summer, with no significant rain for almost 3 months, and about 70 days of 100*+ temps.  My yard and lawn, including shrubs, bushes and trees are watered 2-3 times a week for 20 minutes, plus there is a soaker hose going around the house for foundation watering once a week.
  I would appreciate any advice you can give me!

Charlie

Answer
Hi Charlie,

It sounds like one of your trees is a different variety or has different genetics than the other trees if it is the only one attacked.  Be sure to closely inspect the other trees because they may be more resistant to the problem and show less damage.  However, they may be slightly affected.

You describe the white powdery stuff as being on the limbs.  If it were on the leaves or flowers, I would say you have a powdery mildew problem.  On the limbs, it is more likely a problem with lichens.  These fungi do not harm a tree, but indicate that the canopy on this tree is thinner and the lichens are using the tree to get more light.

The sticky covering sounds like your tree has an insect problem.  Closely inspect the leaves, especially the underside.  Sap feeding insects such as aphids produce a substance called honeydew which is sticky.  You can purchase an insecticide at your local garden center such as insecticidal soap or horticultural oil.  It is also helpful to spray the leaves with a strong stream of water to help remove the insects.  

The drooping leaves is probably due to the extremely high temperatures and drought in combination with the insect problem.  Although you have been watering the tree, the insects are feeding and removing much of the water and nutrients in the leaves.  Be sure that you have been watering your trees enough.  If you dig down, the soil should be slightly moist to at least 8 inches deep.  You should be able to push a probe (stick) into the soil after watering to this depth.  This helps to ensure that water is getting to the deeper roots and is not just at the surface.

Good luck with your trees!