Archive for Saturday, March 25, 2017

Garden Variety: Aphids invade plants in spring

March 25, 2017

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Early spring is a time when many species of aphids are present in the natural world and may begin feeding on plants in the yard and garden. Aphids are small soft-bodied insects that reproduce quickly and damage plants by sucking sap out of leaf and stem tissue.

Aphids vary slightly in size, with most growing to the size of a pinhead at maturity. They also range in color. An infested plant might have several hundred aphids in varying stages of maturity with size and color differences within the species. Sometimes a plant will even have 2 or more species of aphids feeding on it at the same time. They are typically shades of green, yellow, red, and tan with 2 hornlike structures protruding from the tops of their rears.

Plants infested with aphids may turn yellow, curl, and/or pucker from the stress of feeding. If these symptoms are observed, look more closely for the presence of insects. Sometimes aphids hide on the undersides of leaves or down inside the place where leaves are connected to stems.

An infestation may begin with a few young individuals dropped off by winged adults. An aphid can mature in 7 to 10 days and produce 40 to 60 live offspring, almost all of which will be female. Mating is unnecessary for this insect. In a few short weeks, the population can boom to hundreds or thousands of the insect. When the host plant(s) become stressed, more winged adults are produced to carry the population to new plants.

If aphids are present, look also for the presence of predatory insects such as lady beetles and their larvae and green lacewings and their larvae. If the aphid population is low, plants are healthy, and predatory insects are present, the problem may resolve itself and treatment may be unnecessary.

If aphid populations are heavy and there are few predatory insects, consider treatment. The easiest way to control aphids is to hose them off of the plant with water and a high-pressure nozzle. The stream of water knocks the insects off more quickly than they can remove their mouthpart from the plant, breaking it off. They fall to the ground and die. The few insects that survive can usually be removed with subsequent sprays.

For especially heavy populations, insecticidal soap (use a commercially produced one over a DIY mix to avoid burning plants) or products with azadirachtin (neem) are the safest options.

Aphid infestations are also characterized by the presence of the insects’ shed skins (from molting as they grow). Skins look like tiny white flakes on plant leaves and are sometimes more noticeable than the insects themselves.

Honeydew and sooty mold may also be present. Honeydew is a pleasant name given to the what aphids excrete after digesting plant sap. It is a clear, sticky substance. Sometimes in the spring, aphids feed in trees and the honeydew drifts downwind onto cars and windshields.

Sooty mold is a black fungus similar to something that might grow on a loaf of old bread or cheese. Sooty mold is a secondary problem and can generally be washed off but will return if aphids are left uncontrolled.

Honeydew may attract ants, flies, bees, etc. In some cases, ants “farm” aphids for a supply of honeydew in a mutualistic relationship. The ants produce a chemical on their feet that subdues the aphid population and they milk the aphids like dairy cows for their honeydew. The ants also protect the aphids in this relationship.

There are 250 to 300 species of aphids that are plant pests in the U.S. and nearly every plant species is susceptible to some degree.

— Jennifer Smith is a former horticulture extension agent for K-State Research and Extension and horticulturist for Lawrence Parks and Recreation.

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