Spring brings top 11 landscape insects, diseases

By for CAES News
By Stephanie Schupska
University of Georgia

Jule-Lynne Macie’s top 10 plant problems for early spring turned into 11 when she thought about it longer.

To Macie, an entomologist and the Rockdale County Cooperative Extension coordinator for the University of Georgia, the best steps for a gardener with a plant problem are simple. “Know the plant, and know the beast that’s causing the problem,” she said. “And ask the right questions.”

Her top 11 plant problems start with five insect pests.

Fire ants are No. 1. In March and April, Macie said, use a two-step control method. First broadcast a bait, which takes four to six weeks to work, over the whole lawn. Then after three to four weeks, use a drench or dust on any mounds still active. (Drenching mounds with boiling water on warm days can work, too.)

No. 2, white grubs, are mainly turfgrass pests. They eat the roots. To look for grubs, she said, pull back 1 square foot of grass and look. If you see four or more grubs, use a granular insecticide in spring and fall.

No. 3, lace bugs, most often attack azaleas. They cause ugly speckling but won’t kill the plant. “The best control,” Macie said, “is choosing the right planting site for azaleas. In shade, lace bugs don’t seem to be a problem.”

In spring, spray the undersides of the leaves with a garden hose. Or spray with horticultural oil. Save insecticides for later. But don’t wait too long. “The smaller the insect is, the easier it is to control,” Macie said.

This is especially true with No. 4, sooty mold, a disease associated with sucking insects such as aphids, white flies or scale. To prevent sooty mold, Macie said, spray insecticides when these insects are young.

No. 5, bagworms, infect evergreens and, to some extent, deciduous plants. “When they’re young and hatch,” Macie said, “Bacillus thuringiensis, commonly known as Bt, works well.” Otherwise, prune off the silk “bags” and put out an insecticide, especially if you had bagworm problems last year.

No. 6 starts a list of five diseases with “large patch” on zoysia grass. It won’t kill the grass but causes 2- to 20-foot, ugly, brownish patches on zoysia. To solve the problem, she said, “avoid excess moisture and correct poorly drained areas.”

No. 7, fire blight, can destroy apple, pear, pyracantha, quince, blackberry and other plants. It’s tough to get it out once it’s there. Cut out cankers in winter, and spray plants with antibiotics when they’re in bloom. Prune out diseased spots as soon as symptoms appear. “Dip your shears in one part bleach and 10 parts water every time you clip,” Macie said. Don’t overfertilize plants, either, or fire blight will spread fast.

No. 8, Phytophthora root rot, strikes azaleas and aucuba in damp soils at 80 degrees Fahrenheit or above. It retards growth, leaving foliage drooping with off color. “Don’t overwater,” she said. “Plant (resistant plants) in well-drained soil, and put chemicals around healthy plants if you know the site has had a problem.”

No. 9, leaf gall, affects azaleas and camellias. The fungus causes pale green, pinkish swelling. Control is simple. “Prune it off, get rid of it and you’re done,” she said.

No. 10 is spot anthracnose on dogwood, which starts when dogwoods bloom and causes bracts to deform and fall off early. “Spray with fungicide in early spring, just before and during blooming,” Macie said. “It doesn’t cure the disease but will protect new growth.”

Macie chose No. 11 because it generates so many calls.

“Lichens aren’t problems,” she said. “But a lot of people will bring it in and say, ‘this is killing my tree.’ ... Your tree does have a problem, but it’s not the lichen. The lichen will go away if the tree rebounds.”

(Stephanie Schupska is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.)

Stephanie Schupska is a news editor with the University of Georgia Public Affairs Office.