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NOW FOR SOME GARDEN BAD GUYS - APHIDS
by Nanette Londeree, Consulting Rosarian
One of the unwanted visitors to the spring garden arrives just about now. These unsightly, prolific pests donít do much damage and generally donít spread disease, but are offensive mostly because they look bad. Aphids love succulent new growth on your roses. They have high nitrogen requirements, and their populations boom when plants receive a flush of nitrogen. Excess nitrogen also encourages rapid new plant growth, providing an abundance of susceptible leaves for foliar diseases.
Aphids often cluster in large colonies on and below young flower buds and tender unfolding leaves. They feed on plant cell contents and sap by piercing the plant and sucking up the liquids. Really large colonies of feeding aphids can weaken flower bud necks (pedicles) and distort leaf growth. As they feed on the plant they produce honeydew that attracts ants that in turn can be very protective of aphid colonies. In fact, many species of ants are so addicted to this sweet drink that they will protect the aphids from various predators and move them to new plants if the one they are on starts to wilt. Some ants even go as far as to build small shelters over species that feed near the base of the plant and or to keeping root-aphids inside their own nests. All the honeydew that the ants donít consume can end up supporting the growth of black sooty mold.
Adults are green or pinkish with long black cornicles (tube-like projections at the rear of the abdomen), and pear shaped bodies (they are approximately 2 mm in length). The shiny, black eggs live through the winter in protected nooks and crannies on the plant. In the spring, eggs hatch into females that are capable of reproducing without mating. During the warm growing season, aphids reproduce on roses through parthenogenesis. In the fall, triggered by the change in day length, winged sexual forms (males and females) are produced. They mate, and the females lay eggs for over wintering.
These colonies make for easy pickings by aphid predators and parasites, of which there are many. They can be removed by any force, and often it's sufficient simply to knock them to the ground with a shot of water. They are poor climbers and probably will not reestablish, and they run a high risk of getting eaten by ground-roving insect predators. If natural predators or a blast of water isnít enough to control these pesky creatures, try using an insecticidal soap. If that isnít enough, you can try using a botanical insecticide like Neem.
Photo by: Bastian "Bart" M. Drees
Photo courtesy of: Department of Entomology, Texas A&M University
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Last Modified: 08/06/2013