As we get into the budbreak in pecan trees, one insect we should keep in mind is phylloxera. These are small, aphid-like insects that are responsible for causing galls on the leaves and stems of pecan trees during the early part of the growing season. Usually, three species of phylloxera can attack pecan trees: pecan leaf phylloxera (Phylloxera notabilis), southern pecan leaf phylloxera (Phylloxera russelae) and pecan phylloxera (Phylloxera devastratrix). As the name indicates, the first two species attack leaves and cause galls on leaves. The pecan leaf phylloxera primarily attacks the young nursery trees, whereas the southern leaf phylloxera attacks mature trees. The third species causes galls primarily on stems, leaf petioles, catkins, and nuts. All phylloxera species overwinter as eggs on the tree and emerge as adults in the spring. The adults then crawl and find the young plant tissues available right after budbreak. The formation of galls or wart-like structures is the result of the insect feeding and manipulating the leaf tissues to form a gall. Inside these galls, the first female (also called stem mother) from the overwintering generation produces hundreds of offspring, and they feed inside the gall in a protective environment. As the insects grow and their population increases, the gall size also increases, and by mid-May or later, these galls split open to allow the insects to escape. At this time, some of the individual insects will have wings, and they find another spot to lay eggs and continue the next generation. The leaf phylloxera could have 3-4 generations, whereas the stem phylloxera appears to have only one generation per year.
Between the two types of phylloxera, the stem phylloxera is more damaging as it attacks and causes galls on the reproductive parts of the pecan tree. The gall formation process is complex; insects manipulate plant tissues to divert energy and nutrients from other parts of the plant to these galls. Therefore, excessive galling due to phylloxera infestation could hurt the trees and affect production. Besides, heavily infested leaves or terminals bearing nutlets could drop prematurely, thereby impacting the crop. Once we see these galls either on the leaves or on the stems, it is too late to respond to the insect attack; they have already caused the damage. The best approach is to make an application with a product like imidacloprid right after the budbreak once you see the new, young leaves on the trees. Please consult the UGA Pecan Spray Guide for rates and other information. Imidacloprid is a systemic insecticide that is absorbed and becomes available on young leaves following the application. Thus, young leaf tissue will be protected from phylloxera feeding. We often see that phylloxera attacks are limited to small areas within an orchard because they do not move to a greater distance to look for food. Therefore, it is likely that you could experience phylloxera in the same area, and it is a good idea to treat those trees proactively.
An attack by phylloxera in pecans brings along another important insect pest- hickory shuckworm. This is another insect we need to worry about later in the season as they attack developing nuts, primarily feed on the shuck of the nut but can also feed on the nut-meat depending on the stage of the nut. Most insects go through a dormant stage during the winter and become active in the spring as the temperature increases. Likewise, hickory shuckworms also emerge from their overwintering pupal stage, and the adults will be looking to start a generation by laying eggs. However, during early spring, there are no nuts available for the hickory shuckworm to feed on, and they have developed this partnership with the phylloxera and exploit the galls for feeding. Not all, but a good number of the phylloxera galls when you open up in May, you will find a hickory shuckworm caterpillar inside those galls. Since the phylloxera galls support the first generation of the hickory shuckworm population in the orchard, an elevated level of shuckworm infestation on nuts is possible. Therefore, it is a good idea to manage the phylloxera infestation on orchards to reduce the impact of phylloxera as well as reduce the subsequent damage from hickory shuckworms.
