Aphids Causing Sticky Problems For Missourians

Experts are not sure why the tiny insects are so abundant this year, but the Conservation Department has advice for getting rid of them.

JEFFERSON CITY-If your car and patio furniture seem to be getting dirty faster than usual these days, it isn't your imagination. Experts with the Missouri Department of Conservation say the sticky situation is caused by tiny insects, and they offer advice for getting rid of the messy bugs.

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Forest Entomologist Rob Lawrence says Conservation Department offices around the state have received dozens of calls asking why trees are dropping tiny droplets of sap all over vehicles, homes and anything else below. He is telling those callers that the culprit is not trees, but aphids.

"The stuff people are seeing on their cars is actually honeydew," said Lawrence. "It is a sugary, sticky solution excreted by aphids while they feed by sucking tree sap. Reports I am getting indicate that we have huge numbers of aphids in the Kansas City area. This is like nothing anyone has seen in recent memory. The number of aphids seems to be higher than normal in other parts of Missouri, too."

Lawrence said black walnut trees are most affected in the Kansas City area, with pecan, white oaks, hickories, elms, redbuds and sugar maples also involved to some degree. Aphid outbreaks in other areas seem to be affecting a different group of trees, leading him to believe different types of aphids may be involved. Experts have not determined which aphid species are involved.

The cause of the outbreak also is unknown, but Lawrence said some evidence suggests it might be weather-related. He speculated that the complete loss of leaves in the April freeze and subsequent emergence of a superabundance of tender new leaves provided conditions that favored aphid population growth.

Aphids normally do not cause serious damage to trees. However, the massive numbers seen in some areas this year could pose a threat to the health of trees already weakened by a severe freeze in early April. Lawrence said the best thing owners can do to reduce ill effects from aphids is to support trees' general health. Watering is the easiest measure. Slow-soaking the ground beneath trees helps them replace moisture lost to aphids and reduces drought stress.

Tree owners may be able to get rid of aphids in some cases. On small trees, spraying with a strong jet of water can dislodge the insects and wash honeydew off leaves.

Spraying with insecticidal soap can provide effective aphid control and has minimal effects on non-target insects and plants. This treatment requires direct contact with the aphids, so thorough drenching of foliage is necessary. Read label directions carefully before use, because a few tree species, such as hawthorn and plum, are sensitive to soaps.

Other chemical treatments also are available. For information about these, visit ohioline.osu.edu/hyg-fact/2000/2031.html or extension.missouri.edu/explore/agguides/pests/g07274.htm.

The sugar in honeydew may attract bees and flies, and it encourages mold growth, turning leaves and other surfaces black. This is not harmful to trees, but the unattractive appearance can be avoided by washing with water. For more information, visit ohioline.osu.edu/hyg-fact/3000/3046.html.

Source: Missouri Department of Conservation