Q. My crepe myrtles seem to get shiny, sticky leaves each year followed by a black mold, which causes the leaves to drop off. It took me a while to figure out that the shiny, sticky leaves were caused by aphids and their excrement, and that the mold was a fungus growing on the leaves living on the excrement. The problem is that I can’t quite figure out how to intervene in the process, so we get more blooms and less problems. What are your suggestions? I have sent you some photos of the aphids and the plants. 

A.The photos you sent reveal that your crepe myrtles are small, and aphids are easy to kill, so if you watched closely and sprayed almost any insecticide or even a soapy solution at first sign of an infestation, you should be able to stop the process that you described where the leaves end up with sooty mold. The advantage of using an insecticidal soap  is that it has less impact on the beneficial insects than a more potent insecticide like acephate or malathion would. Spray off the aphids every week with the soapy solution from a hose end sprayer.  One of your photos shows predatory insects feeding on the aphids. It would be ideal if ladybug adults and larvae would increase to the point that they would control the aphids. Have you ever just let them be to see how quickly the predators increase? 

Q. We want to plant a row of crepe myrtles but don’t like the powdery mildew that some of the plants develop. Is there a spraying strategy to eliminate mildew on crepe myrtles or is it a matter of picking the right varieties?

A. It is a matter of selecting the right varieties. Your favorite retail nursery should have a varietal list that relates the selections’ size, flower color, and mildew resistance. You can also visit plantanswers.com to review the mildew susceptibility of crepe myrtle selections. 

Q. We moved from Michigan and are trying to understand the tomato gardening here in Central Texas. Our local nursery when we asked for tomato plants said that we had to wait now until after mid-July to plant a fall crop!

A.Yes, we have two short tomato seasons — from March to the end of June and then from late July through Thanksgiving. We use “determinate” varieties that reach full size quickly and then concentrate on setting and maturing fruit. In the spring, the plants are trying to beat the hot weather, and in the fall the plants must beat the cold weather. Some of the recommended varieties in the fall will be Tycoon, HM 8849, 444, BHN 968, and Valley Cat.

Q. When is the last time that it is reasonable to plant California Giant, Cactus, and other zinnias by seed? We want them for cut flowers and for butterfly nectar. The Dreamland and other hybrid transplants on the market are too short.

A.I will seed zinnias as late as August with the expectation that they will bloom into December. Last year was an exception because of the record low freezes in mid-November.

Q. How can we protect our ripening peaches, tomatoes and blackberries from the birds? Mockingbirds, cardinals and other species are ruining a large portion of the crop!

A.It is not easy to use bird netting but that seems to be the best solution.

 

Calvin Finch is a retired horticulture agent in Bexar County. He writes for and works with a number of area media outlets.

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