#7 in our series on America’s Most Unwanted garden pests is the all-too-common aphid. Aphids otherwise known as plant lice, are tiny soft-bodied, sucking insects. With over 4,400 types of aphid worldwide, they are the most common garden pest. Most aphids only target one kind of plant, while others have a much broader diet.
These tiny (1/32”) pear-shaped insects can be
winged or wingless and almost any color. A colony of aphids can cause
substantial damage to plants, trees and shrubs including yellowing or curling
leaves and stunted growth. In addition to sucking the juices from plants, their
saliva is actually toxic to many plants. Aphids often transmit fungi and
disease to the plants they infest.
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| Aphids with their ant bodyguards Source: E. Bradford Walker, Vermont Dept. of Forests, Parks and Recreation; Bugwood.org |
In the process of feeding, aphids secrete a sticky,
sugary liquid called honeydew -- which can rain down from the trees on anything
below it, like your car or lawn furniture. Given the size of an aphid, when
there’s enough honeydew to drip from a tree, you know that there is a huge
population feeding above.
The sweet honeydew is attractive to ants. Many
sugar-eating ants actually act as body guards to aphids: they protect them in
order to milk the aphids for honeydew. In addition to the damage aphids cause
directly, the honeydew can make plants more susceptible to fungi, like sooty
mold.
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| Potato Aphids Source: David Cappaert, Michigan State University:Bugwood.org |
Inspecting plants for aphids is the first step
towards controlling this pest. Many aphids are well camouflaged to blend with
the plants they target. Their coloring – along with their tiny size – means
aphids are often overlooked until they are so numerous that they coat the plant.
Aphids are a preferred food of beneficial insects like ladybugs, predatory
wasps and lacewings; a sufficient population of these species can keep aphids
under control.
If aphids have populated a plant or shrub, a
stream of water from a garden hose can sometimes dislodge them; although flying
aphids are likely to return, crawling ones often won’t make it back to the
plant.
Because of the potential damage from aphids, as well as the diseases they transmit, it is wise to begin controlling aphids at the first sign of infestation. Almstead arborists offer both organic and traditional methods for control. Often a single application in spring is sufficient to keep aphids in check.
