DFW gardeners asking about brown spots, falling leaves & flying pests. What to know
This is the time of year that gardeners’ questions take a decided turn. I’ve stacked them up and assembled the top ones here for your viewing. See how many are falling true to your experiences.
“Why are my trees dropping so many leaves?”
This happens every year, most noticeably to large-leafed, fast-growing species like sycamores, cottonwoods, silver maples, catalpas, and fruitless mulberries, among others. We had abundant spring rains before the hot, dry weather set in back in June. This week’s respite has been nice, but the trees had already started shedding some of their “responsibilities” by dropping older leaves (those farther down on their stems). The remedy: water deeply and see if the premature leaf drop doesn’t stop. At the same time of course, you’ll want to watch for any signs of trunk or root damage that might be contributing.
“My St. Augustine has brown spots, but fungicides aren’t helping at all. What’s the problem?”
We’ve talked about chinch bugs several times already this summer, and this is the prime clue. They always attack St. Augustine in the hottest, sunniest parts of your yard. The grass will appear to be dry (folded blades with an oily, dark green color), but it doesn’t respond to watering. That’s when you need to get down on all fours and look for the BB-sized black insects at the edges of the impacted turf. They’ll have irregular white diamonds on their backs, and they’ll be moving about freely. Your local nursery or other garden supplier will have several products labeled for their control. Don’t delay. Chinch bugs can kill large patches of turf in a hurry.
“The leaves of my crape myrtles are really sticky. What causes that and what can I do to stop it?”
Two insects can do this (but not a fungus). Crape myrtle bark scales will congregate on the plants’ trunks and twigs. They’ll look like white ashes attached to the stems. When pressed with your thumbnail any live scales will exude a red fluid.
Crape myrtle aphids congregate on new growth. You’ll see the pear-shaped pests in large numbers, as flowers and fallen leaves are stuck together by the gooey honeydew they exude.
Both of these pests can be stopped by use of a systemic insecticide. Texas A&M research has shown Imidacloprid to be the most efficient. At this time of year, you’ll need to apply it as a spray, but the better control will be had by a mid-May application as a soil drench.
You may also see a black lady bug beetle with two bright orange dots on its wings. That’s the twice-stabbed lady bug, and it’s a very effective predator of this pest. If you see them withhold any insecticidal sprays for a few weeks to see if they do the job for you.
“Is it too late to plant new grass in my lawn?”
Not at all. Early September is generally considered to be the cutoff time for seeding bermuda and for sodding St. Augustine. You can sod bermuda even later into the fall. You will need to be extra-attentive to its water needs. If you’re sowing bermuda seed, be prepared to water morning and evening for a few minutes each time. New bermuda roots are quite shallow, so you must keep the surface of the soil moist for the first two or three weeks. Sod has a slightly greater margin of error, but you’ll still want to water daily for a week or two.
“A couple of hollies that I planted last spring have turned brown. I don’t think they got too dry. What else could have happened?”
I’ve grown hollies all of my adult life, and I can’t think of any other possible cause. Hollies do not wilt like most plants do. Their stems and leaves are too leathery. When the plants get too dry, they just lose their luster and change from a glossy dark green to dull olive drab. That’s when you know you’ve let them go too far. Even if you have a few branches that still have a few green leaves here and there, waiting for them to fill in will be a years-long painful experience. It’s best to admit the mistake and replace them. Next time, water them by hand using a garden hose with a bubbler or breaker. Apply 5 to 20 gallons of water every two days during the summer. The larger the plant, the more water it will get with each irrigation.
“What are the huge wasps that fly slowly close to the ground? Are they dangerous?”
Those are most commonly known as “cicada killers.” Their season runs concurrent with the noisy cicadas, generally June and July. They come out of their ground nests and hover slowly as they search out their prey. When they spot a cicada, they attack from above. They land atop the hapless cicada and start paralyzing it as they carry it back to their nest. Once there they take it underground and encase it as they lay their eggs in its body. The larvae develop within the decaying cicada, feeding and emerging the next year to repeat this horror-movie theme as they have through the ages.
As to whether they’re dangerous: only if you try to capture them or surprise them. Otherwise, they’re docile beneficial insects. I work in my garden with them flying around me. They’re just another of the many marvels of nature.
