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Azaleas, St. Augustine can face shade problems
MISSISSIPPI STATE -- Months after Hurricane Katrina tore through Mississippi and Louisiana, the storm is still doing damage to landscapes.
Blake Layton, entomologist with the Mississippi State University Extension Service, said some effects of landscape trees damaged or destroyed by Katrina's winds are only beginning to be felt. Many azaleas and St. Augustine lawns that once thrived in the shade are now in bright sunlight.
“Following the loss of key shade trees, it's not uncommon for St. Augustine lawns that never before had problems with chinch bugs to suffer heavy damage,” Layton said. “The same is true for lace bugs on azaleas that experience increased sun exposure.”
Katrina did the most damage in coastal areas where St. Augustine lawns are common and azaleas are abundant. Homeowners can't prevent these pests from attacking their plants, but they can be more vigilant in scouting for the insects.
“You will have a better chance of success if you detect the chinch bugs or azalea lace bugs early on rather than after you have a dead, brown lawn or damaged azaleas,” Layton said.
Chinch bugs have piercing/sucking mouthparts and when they feed on grass stems, they inject a toxin. In highly infested areas, this toxin causes the grass to turn yellow, then brown and eventually die. A chinch bug infestation can lead to disease and other lawn problems.
Adult chinch bugs are black insects about one-fifth an inch long with white wings folded over their backs in an “X.” Newly hatched nymphs are red with a light-colored band across the back, and older nymphs are black. Scout for chinch bugs in turf by parting grass stems and looking for the insects in the crown region or running across the exposed soil.
“Another scouting method is to remove both ends of a gallon-sized can, press one end of it 2 to 3 inches into the turf and fill it about half full of water,” Layton said. “If chinch bugs are present, they will float to the top within a few minutes. Check several sites, choosing areas where green St. Augustine grass meets yellowed, dying grass.”
There are a variety of insecticides labeled for use against chinch bugs in home lawns. Read all label directions carefully and only apply as directed.
Wayne Wells, Extension turf specialist, said St. Augustine tolerates shade well, but it also does fine in full sun.
“Its management may entail slightly more frequent watering as transpiration will increase with higher temperatures under the more intense light,” Wells said. “You also have to be more observant for chinch bugs that like hot, dry conditions provided by full sun locations.”
Lace bugs are the most common insect pests of azaleas. Layton said most azaleas have lace bugs, but healthy plants in ideal conditions are more tolerant of the pest than are stressed plants.
“When heavy infestations occur, they can cause extensive, unsightly damage to the azalea,” Layton said. “Both the nymphs and the adults feed on the undersides of the leaves with their piercing/sucking mouthparts. This gives leaves a stippled appearance as light-colored spots appear on the upper surface of the leaves as a result of the bugs' feeding.
“Heavy infestations cause leaves to have a bleached appearance, and it can take quite a while for azaleas to fully recover from severe injury once the bugs are controlled,” he said.
Adult lace bugs are about one-eighth inch long with lacy white wings and dark markings. Nymphs are smaller, dark-colored and covered with spines. Lace bugs overwinter as eggs and nymphs hatch in early spring.
“Plantings can experience heavy infestations by mid-April, but there are several generations per year, and populations continue to build all summer,” Layton said. “Routinely check azaleas for lace bugs, and initiate treatments if significant numbers are detected.”
As with chinch bugs, there are a variety of insecticides labeled for use against azalea lace bugs in home landscapes. Read all label directions carefully and only apply as directed.
Norman Winter, Extension horticulturist, said those who are trying to reestablish landscapes should remember that azaleas require the filtered light provided by established trees.
“If you want trees again, you should definitely replace them now. You won't get the shade that a 300-year-old oak provides, but you can plant quality trees that will one day make an impact in your landscape,” Winter said.
He recommended live oaks, magnolias, red maples, bald cypress, dogwoods, redbuds and crepe myrtles as quality trees that can replace ones damaged or destroyed.
“If you had a shade garden but lost your shade trees, you have a changing garden now, and it could be even prettier than before,” Winter said. “You may have to move some of your shade-loving plants or give them to someone who still has shade, but there are many sun-loving plants that you can replace them with.”