Those landscape plants may be just what you wanted, but before you take them home, check them closely anyway. You may find some unwanted hitchhikers.
"Aphids are hard to control in a greenhouse or nursery environment," said Beverly Sparks, an entomologist with the University of Georgia Extension Service. "By the time they get to the garden centers, many plants can have small aphid populations."
You don't want aphids on your backyard guest list. "They have mouthparts like little soda straws, which they use to suck juices from plant cells," she said. The feeding weakens plants and causes wilting, but that's only part of the problem.
The tiny gluttons suck up more plant juices than they can digest. The part the aphids' bodies can't use passes through them as a high-sugar excretion.
This sticky "honeydew" drops onto leaves or anything else beneath them. And to add the final insult, various fungi feed on the honeydew and create a black coating, called sooty mold. It's not a pretty picture.
The worrisome pests are so small you can hardly see them. "The problem," Sparks said, "is that populations can build to such large numbers that they cause serious injury to plants."
Aphids infest almost any annual or perennial plant and many of the more common woody landscape shrubs. Two species causing problems in late April were green peach aphids and melon aphids.
"As the weather warms," Sparks said, "we'll see more problems with crape myrtle aphids."
One way to keep aphid populations down in your yard, she said, is to avoid buying them on new landscape plants.
"Check closely for signs of wilting, curling of new growth and sticky upper surfaces on lower leaves," Sparks said. "Look for the aphids themselves on the stems and underside of leaves on the newest foliage."
To see the aphids, she said, use a hand magnifying lens. Or shake the foliage over a piece of white paper. The soft-bodied insects are the size of a pencil point.
Looking at their rear ends through a hand lens, she said, you can see what looks like two tiny tailpipes. Aphids are the only insects with these dual- exhaust cornicles.
If you find the little hitchhikers, look for other plants, Sparks said. You have enough problems at home without buying more of them.
If you already have aphids on plants in your landscape, check closely to see if you also have beneficial insects. "Lady beetles can clean up an aphid population," she said. "Don't treat for aphids if you have good populations of lady beetles or lacewings."
If you don't have enough good bugs, you'll have to get rid of the aphids yourself.
The pests will be concentrated on the newest leaves and stems. So carefully prune off the heavily infested foliage. Put the pruned parts into a plastic bag and get rid of them.
You can also spray plants with an insecticide labeled for aphids or use an insecticidal soap. Whatever you use, though, be sure you spray the right places.
"To control aphids," Sparks said, "you have to get thorough coverage on the underside of the leaves."
(Dan Rahn is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.)