Neil Sperry

‘Why is my St. Augustine burning up?’ Some answers to your big gardening questions

Want to plant a garden but aren’t trying to rip up your whole yard at once? Try this strategy

Learn a simple, add-as-you-go strategy for building a backyard oasis.
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Learn a simple, add-as-you-go strategy for building a backyard oasis.

I try to answer some of the most-asked questions on gardeners’ minds here every few months. I just checked my list, and I’m apparently way overdue. They’ve been piling up like Sahara dust against the east walls of our homes these last several weeks, so let’s plow into the big ones.

“Why is my St. Augustine burning up? I’m watering it a couple of times weekly, but it’s just getting browner.”

You’ve described classic symptoms of chinch bugs, and this looks to be a record year for the little pests. They’ll always be in the hottest, sunniest parts of your yard (never in shade), and watering won’t give the normal results when the grass begins to look dry. Confirm their presence by parting the grass and looking for BB-sized black insects with irregular white markings on their wings. The immature nymphs will be red. Treat with Imidacloprid to stop them. Don’t delay. They can quickly kill big portions of your lawn.

“My bermuda lawn has oddly shaped areas that are completely brown. I water deeply, so I don’t think it’s that. What causes that?”

That’s Pythium, more commonly called cottony blight. It’s a summer disease that shows up in bermuda that is kept overly wet or that has been fertilized to excess. You might get some relief from application of a labeled turf fungicide, but cutting back on the water and nitrogen might be of more help.

“My trees’ leaves are starting to turn yellow, especially the ones at the bottoms of the trees. Are they dying?”

Not at all. That’s a tree’s natural way of coping with extreme heat, dry soils and low humidity. It sheds some of the responsibility of maintaining lush foliage it produced back in the spring when conditions were much more favorable. Water them deeply every week or two and they’ll be just fine.

“The leaves of my cannas and vinca groundcover are turning brown and sticking together. What is it, and what should I do?”

Not surprisingly, these are called leafrollers. They’re a category of insects that ties leaves together to form protective cocoons. You’ll also see them attacking redbuds, sweetgums, persimmons, pyracanthas and cotoneasters. There is no way to get them out of the leaf wraps once they’re secured, but you can apply a systemic insecticide ahead of time to kill them as they begin feeding and forming the cocoons. Again, Imidacloprid is the product of choice. It needs several weeks of lead time. For cannas and trailing vinca groundcover, allow 2-3 weeks. For shrubs and trees, 4 to 5 weeks.

“What are the large bees I see hovering close to the ground? They seem to come out of the ground. Are they dangerous if I have pets and children outside?”

You’re probably talking about cicada killers, also called ground hornets. On the balance, they are beneficial insects. They are predators. They fly low to the ground watching for cicadas to emerge and fly. They attack the cicadas, landing atop them and causing a terrible ruckus as they sting and paralyze the victims. They fly in tandem back to the cicada killers’ ground nests where they take the dying cicadas into their tunnels to serve as food for developing larvae. It makes for an interesting story, and you’ll enjoy telling it as long as you leave the predators alone. Don’t try to swat at or capture them, and don’t dig where they’ve built their nests. It’s a rare day when a gardener or pet gets stung, but they’re very painful.

“Why did my tomatoes do really poorly this year? I didn’t get many fruit, and then the plants just burned up when it turned hot.”

Several factors probably combined. We have fewer good varieties available to us now than ever before. You want to grow small and mid-sized types, and you must avoid the large-fruiting varieties like Big Boy and Beefsteak. They simple will not set fruit when it turns really hot (above 90 degrees), as it did really early this May. As for the plants’ “burning up,” that was probably due to spider mites. They’re nearly microscopic, yet they’re the most damaging pests we have in Texas gardening. You’ll first notice tiny tan mottling. Then entire leaves start to turn light tan or even white, then dried and crisp. It almost always begins at the bottoms of the plants, and it spreads upward and outward. If you thump the affected leaves over white paper you’ll be able to see the mites moving around. General-purpose insecticides and summer-weight oil sprays will reduce their populations, but your biggest helps will be to plant early (late March) and to plant a fall garden (set transplants out by early July) so you can grow the plants when the mites aren’t as active.

“My rose plants look terrible, and their stems are filled with little thorns. Can I save them?”

No. That’s rose rosette virus, and it is, sadly, fatal with no prevention or cure. It has become epidemic in the Fort Worth/Dallas area for the past 7 or 8 years. You need to remove the infected plants immediately, roots and all. Put them in black plastic trash bags, tie them shut and send them to the landfill. Replant with dwarf crape myrtles or some other unrelated plant species.