Improper pruning of crape myrtles invites pests

Q: At the end of last summer, we noticed our crape myrtles were covered with a black sootlike powder. It even discolored the pinestraw beneath. When we pruned back the trees recently, we still noticed it. How should we treat?

JULIE CLYBURN, Forsyth County

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WALTER REEVES/Special

Sooty mold grows on plants infested with sucking insects like aphids, whiteflies or scale.

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A: Your problem is caused by what you just did: pruning back your crape myrtles. The lush growth that results from a heavily pruned crape myrtle attracts aphids, which produce honeydew, on which black sooty mold grows.

Pruning crape myrtles back to a knob is a great way to exacerbate problems with insects as well as powdery mildew. Consider applying a systemic insecticide (Bayer Tree & Shrub, etc.) now to kill aphids in summer. I have pictures of correctly pruned crapemyrtles at xrl.us/PRUNECRAPE.

Q: I have a large zoysia lawn. I’m looking for the best type of pre-emerge to put down now. Is 5-10-15 the way to go?

ADAM KARWOSKI, e-mail

A: I am totally against fertilizing zoysia, bermuda, centipede or St. Augustine lawns when they are not green. You waste money and you may harm the grass if it is fed too early.

Early March is a good time to apply a pre-emergent but it is usually not necessary on zoysia lawns. A vigorous zoysia lawn is quite able to choke out weeds. If you have bare spots, use a straight pre-emergent like Dimension, Halts, or Crab-Ex. Do not fertilize until your zoysia is 90 percent green.