Yellow Aphids on pecans are a common pest anywhere pecans are grown. They can show up any time during the summer but numbers tend to explode during the later parts of summer. An Aphid is sexually mature in 5 days and can produce 5 offspring per day for up to 30 days. Numbers can get out of hand very quickly
Aphids are sucking insects that feed on the sap in the leaves. This activity takes nutrients from the tree weakening it. Aphids will not usually kill a tree but they can and do negatively impact current season nut crops and the trees ability to have the energy store for the next years nut crop. By reducing the energy in the tree, this years nut crop may have nuts of smaller size. By reducing over winter reserves, next years flower production can be affected meaning fewer nuts next year.
Besides Yellow Aphids, Black Aphids can also be an issue. They have a similar effect of tree health and are more common in some areas. Pecan trees can have both aphids on them at the same time. Usually one is more abundant than the other. Some pecan varieties are more attractive to one aphid over the other.
Direct feeding is one problem caused by Yellow Aphids on pecan trees. The other effect is caused by a byproduct of Aphid feeding, Honeydew. Honeydew is a liquid that is high in sugars that is excreted by feeding aphids. As it falls, it lands on the foliage and the leaves become sticky and shiny with this sugary substance as seen below. Honeybees are highly attracted to honeydew especially during dry weather when other nectar sources are in short supply. Honeydew also feeds sooty mold which forms on the honeydew on the leaves. This sooty mold blocks sunlight from reaching the surface of the leaves and further reduces the leaves ability to feed the tree. If a leaf is heavily covered, it can be dropped by the tree.
Honeydew on pecan leaves.
Yellow Aphids on pecan trees have several natural enemies. Ladybugs and lacewings being the primary predators, there are many other insects which eat or parasitize aphids. Since predators need an ample food source, they always follow behind the population explosion of aphids. While natural predators sometimes catch up to an aphid outbreak and bring it under control, the honeydew and sooty mold remain behind to hinder photosynthesis for the remainder of the growing season.
Controlling aphids is fairly easy. There are several common insecticides that will kill them. The probem comes in with collateral damage. Most of the common pesticides that are labeled for aphids also kill their predators and honeybees. There are two products that use Flonicimid as their active ingredient that disrupt aphid feeding thus starving them without harming their predators or honeybees feeding on honeydew.
There are several other pecan pests which will need to be dealt with using more potent broader spectrum products but, if we handle aphids in a timely fashion and thus reduce the presence of predator insects and honeybees in our orchards. we can use these other products knowing we have reduced collateral damage to our beneficial insects.