Aphids make their move

Pat Munts  /  Staff writer

Shawn Hanson of Senske Lawn and Tree Care points out the larvae stage of aphids on the underside of this leaf. They look like small bumps. (File/The Spokesman-Review) Controlling aphids Shrubs, small trees According to Deffe and Ben Kappen, arborists for Northwest Plant Health Care, controlling aphids is an exercise in persistence and patience. •First, plant varieties that are resistant to aphids or shrug off infestations better than others. •Second, just getting the bugs off the plants reduces the problems. Use a hard stream of water to blast the bugs off sides of plants you can easily reach. •Encourage predator insects that will seek out aphids for dinner. The aphid population will build to a certain level and then the lady beetles, lacewing larvae and hover fly larvae will move in and lay eggs or eat the aphids. •The next level of control is to use insecticidal soaps. These soaps attack the soft exposed tissues of the aphids killing by contact. This means that the soaps have to be applied so they reach the aphid. Insecticidal soaps, however, will also kill the predatory insects that, given some time, will control the problem. An alternative is to use a systemic insecticide that is picked up by the plant's vascular system. When the aphid mainlines the sap, it picks up the chemical and zap, it's history. The advantage to this is that the systemic insecticide does not affect the predator insects. So the aphids are caught between the predatory bugs and the drugs. Large Trees According to Kappen, trees you can not easily reach all parts of take a different strategy to control the aphids. It may be time to call in the professionals. •First, the time to treat a tree for aphids is NOT when they start creating honeydew. It's long before that. Systemic controls picked up by the tree's sap are the most effective long-term method to control the aphids in large trees. According to Kappen, it takes about four months for a large tree to move the treatment from its roots to the top of the canopy. Generally, that means commercial applications for aphid control must be done in August or September or very early in the spring. •Second, controlling aphids on large trees takes chemicals, skill and equipment that are difficult or expensive for the home owner to obtain at an affordable rate. Commercial applicators are licensed to use chemicals which are not available to the homeowner, but are very effective and target just to the aphids.

"I have never seen so many or different kinds of aphids," exclaimed Cindy Deffe, environmental sciences instructor at Spokane Community College. On a recent walk on the SCC campus with her horticulture students, they found aphids everywhere, even in her classroom where she has a number of live weed plants set out for study.

"I have to keep washing them off the plants," she said with a chuckle.

For their size and seemingly simple appearance, aphids are very complex critters. They are small (1/16- to 1/8-inch long) insects that range in color from green to brown, purple, red and black. Most are soft-bodied covered in an exoskeleton while others protect themselves with a waxy, cottony covering. The tell-tale identification marks of aphids are long thin legs, sucking mouth parts, long antenna, a pear-shaped body and a pair of tiny tubes that project from the bug's posterior. There are literally dozens of different varieties of aphids and most attach themselves to specific plants: rose aphid to roses, cherry aphid to cherry, green peach aphid to peach, Norway maple aphid to maples. The list is endless.

Aphids are masters of reproduction. They over-winter as eggs or adult "stem mothers" on the trunks, branches and roots of host plants. Some aphids stay on a single plant group. Others alternate between different types of plants. The over-wintering eggs hatch as females that can produce live young in less than 10 days. They move to the underside of the leaves where they tap directly into a plant vein and begin sucking on plant sap. Talk about sugar junkies mainlining their fix.

As the colony grows, winged aphids are produced and these fly to a new plant where they begin a new cycle. That means multiple generations are produced over a season. At the end of the season, they change their reproduction to produce eggs which are laid on a variety of plants to over-winter yet again.

Are you totally confused yet? Don't worry. According to Deffe, because of the complexity and variability of aphid life cycles, scientists are just beginning to understand the details of the cycles and reproduction. Some day, she says, we may be able to use the research to find better environmentally friendly methods to control them.

Aphids' damage to plants is more of an annoyance and a nuisance to humans who use or enjoy the plants, than to the plants themselves. Even when infestations are heavy and a lot of foliage is distorted, aphids are rarely the cause of a plant's death.

The main problem with aphids is the sweet, sticky honeydew they excrete, which then drips onto foliage and anything under the plant or tree. The results are sticky, shiny leaves, tiny drops on cars, lawn furniture and virtually anything parked under the offending plant.

To compound the problem, the honeydew attracts ants that feed on the sugar-rich liquid. Ants will actually care and tend the aphids to keep them producing. They will fight off other insects including predators looking for the aphids. If you have ants running up and down plants, look under the leaves for aphids.

Other signs that aphids are present are twisted and distorted foliage and flowers caused by the aphids' feeding. Another is the presence of a sooty black mold that grows in the sugary honeydew.