San Antonio Express News
Sunday, August 17, 2003
By Nathan Riggs, CEA-IPM, Texas Cooperative Extension-Bexar County
The hottest part of the year is here, and South Texas is once again bathed in the heat and humidity of August. Our lawns, landscapes, and other plants are welcoming any drop of water they receive and just waiting for rain and cooler temperatures. Not only are plants being affected by the scorching heat, but a few insects are taking advantage of the conditions as well.
The type of plant determines its resistance to the sun’s heat. Succulent plants that store water within their leaves, such as aloe vera, cactus, and kalanchoes, can withstand dry conditions much longer than plants with large, thin leaves. Grasses such as bermuda and buffalo with their thin blades can also resist water loss much better than wide-bladed grasses like Zoysia and St. Augustine.
Established plants and trees have sufficient root systems to collect the water needed to stay alive. The way to encourage healthy root systems is through periodic, deep watering to send those roots deeper into the soil. Adding extra mulch or compost to a lawn, flowerbed or around a tree also keeps vital moisture in the soil from evaporating into the atmosphere.
Plants not receiving adequate water can become stressed, leading to disease infections or insect infestations. One example of this is turf grass.
When St. Augustine lawns in full sun become water stressed in July and August, they fall victim to attack by chinch bugs. Chinch bugs suck the sap from the grass at the crown point where the blade emerges from the runner, or rhizome. As they feed on the sap, chinch bugs release their saliva into the wound, causing the grass to turn yellow and die. This pattern usually begins at a central point and radiates in a circular pattern outward.
Test for chinch bugs by drenching an area on the border of the sick grass with a soapy solution (2 tablespoons of liquid soap to 1gallon water). If chinch bugs are present, they will emerge from the grass. Chinch bugs are grayish black, with white wings, and bodies up to 1/4 inch long. Treat a 15 foot radius around the damaged area with a liquid insecticide containing permethrin or pyrethrins.
Another unlikely insect victim during extended periods of hot, dry weather is live oak trees. Healthy live oak trees can pretty much resist most diseases and insects. Stressed trees can occasionally be infested with small numbers of wood boring beetles. The larvae of these beetles will feed on the non-living heartwood of the tree for anytime between 1 and 8 years before emerging from the tree as a adult. Live oaks infested with borers usually show no signs of illness except for exit holes on the trunk or limbs. Treat the trunk and limbs with a borer spray in June and late July to not only kill eggs on the bark, but beetles alighting on the bark and possibly newly emerging beetles.
Extension has an informative publication, “Wood-boring Insects of Trees and Shrubs.” To receive one, send a self-addressed, stamped #10 envelope to Texas Cooperative Extension, 3355 Cherry Ridge, Suite 212, San Antonio Texas 78230.
Nathan Riggs is a certified Entomologist and Extension Agent-IPM, with Texas Cooperative Extension in Bexar County. For more information, call 210 / 467-6575.