One of the more serious pests that affect pecan trees is the black pecan aphid. Pecan growers should be scouting for the black aphid from now through the end of the season. The black pecan aphid can cause serious damage to leaves that can result in premature defoliation. Black pecan aphids cause the area of the leaf that they feed on to turn yellow and stop being photosynthetically active. If you are seeing yellow spots on your pecan leaves it is likely because of black aphid feeding. If enough damage to the leaf occurs then the leaf will fall off prematurely. When premature tree defoliation occurs it is likely that the following year’s crop will be negatively affected. It is important to keep as many leaves as possible on the tree in as good of shape as possible for as long as possible to increase the chance of a good crop the following year. Longer leaf retention will result in increased energy storage which will result in greater tree health and nut production. Because of this it is important to control black aphids. Some varieties are more likely to have problems with black aphids than others. Sumner, Schley, and Oconee are three pecan varieties that are more prone to black aphid damage. Generally black aphids are a pest that occurs later in the season, but they can cause problems earlier in the season. Regular scouting is important because insect pests do not always behave the same way each year. The University of Georgia threshold is to treat when: Before July first 25% of compound leaves have two or more black aphids and after July first if more than fifteen percent of terminals have more than one black aphid and black pecan aphid nymph clusters are found. Nymphs are the wingless olive colored offspring of the black aphid. When you start seeing black aphid nymphs it is usually time to treat. Yellow aphids are also an aphid species that affect pecan trees. Yellow aphids can also be a problem as they suck the sap out of the leaves and excrete a sticky shiny substance called honeydew on the leaves. A fungus called sooty mold can grow on the honeydew and reduce photosynthesis greatly. Rainfall can help to wash the honeydew off of the leaves. The UGA threshold for yellow aphids is 20 per compound leaf. Some good control options that will kill black and yellow aphids at the same time are closer and carbine. The neonicotinoid insecticides such as immidacloprid should work on black aphids, but there is reported yellow aphid resistance to these insecticides. There are other broad spectrum insecticides that can be used for aphids such as chlorpyrifos, but the general UGA recommendation is to try to avoid using these until pretty late in the season if you have to use them.