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| Yellow aphid | Yellow aphid |
Aphids are small, soft bodied insects that suck sap from pecan leaves. There are two species of "yellow aphids," the blackmargined aphid and the yellow pecan aphid. Both species are bright yellow and their injury, biology and control are similar.
Damage: Yellow aphids have piercing-sucking mouth- parts for removing water and plant nutrients from leaf veins. As they feed, aphids excrete large amounts of excess sugars. This sticky material, called honeydew, collects on leaves. Honeydew serves as a food source for sooty mold which can cover leaves during conditions of high humidity. The shading effect of sooty mold can reduce photosynthesis. Studies have also shown that aphid feeding can reduce leaf efficiency and large, late-summer infestations can defoliate trees. This leaf injury and loss can reduce cur- rent and subsequent yields and quality because of lower carbohydrate production.
Biology: Yellow aphid eggs survive the winter hidden in bark crevices on twigs and tree trunks. Immature aphids, called nymphs, hatch from the eggs in the spring and begin to feed on newly expanded leaves. Nymphs mature in about a week and give birth to live young. All individuals are females that reproduce without males during the spring and summer. In late September and October, males and females develop and females deposit overwintering eggs.
Aphids have a short life cycle and high reproductive capacity, so infestations can quickly increase during favorable conditions. Yellow aphid infestations often reach a peak by mid-summer and then suddenly decline after 2 to 3 weeks. Natural enemies, including lacewings, lady beetles, spiders and other insects, can suppress aphid infestations if they are present in sufficient numbers. Insecticides applied for aphids or other pests can sometimes destroy these natural enemies, allowing aphids to increase to even greater densities than before treatment.
Control: Frequently inspect leaves to monitor yellow aphid densities. Examine trees throughout the orchard to obtain a representative sample. Yellow aphids increase more rapidly on some varieties (e.g., Cheyenne) than on others. Treatment should be considered when yellow aphids average 25 or more per compound leaf. Scouting the orchard on a 4- to 5-day schedule will determine if yellow aphid numbers are increasing or decreasing and indicate the need for insecticide treatment. Do not base the need for treatment on the amount of honeydew alone, as infestations often decline rapidly ("crash") because of weather or physiological effects. Thorough spray coverage is important in controlling aphids.
Insecticides do not consistently provide adequate control of yellow aphids. Aphids may become tolerant to an insecticide used frequently in an orchard. An insecticide that is effective in one orchard may be ineffective in a nearby orchard. A number of studies have shown that in some cases the application of pyrethroid insecticides (Asana® Ammo®, Cymbush®) for casebearer or aphid control may be followed by large increases in yellow aphids.
Several soil applied systemic insecticides are registered for aphid control in pecans. These treatments are preventive and may be justified in areas where aphids annually exceed economically damaging levels. The use of these soil applied insecticides is discouraged in areas where ground water contamination could occur.