This spring, an influx of unusual tissue growth has been reported from small pecan orchards and hobbyists across Northeast Georgia. This tissue growth has been seen on the pecan stems, leaves, and even developing nutlets across pecan orchards north of I-20. The culprit is phylloxera. Three species of phylloxera affect pecans: pecan phylloxera, pecan leaf phylloxera, and southern pecan leaf phylloxera. Of these, the pecan phylloxera, otherwise known as stem phylloxera, is the only one that causes economic damage.
Andrew Sawyer (UGA Area Pecan Agent) noted his first observation of stem phylloxera in 2023, when reports of older ‘Stuart’ and ‘Schley’ varieties shedding leaves in early June occurred. This year, calls related to phylloxera have come from across North Georgia, with Morgan County the southernmost report and Lincoln County the northernmost. These calls are typically coming from older, small orchards with less management such as those used for hobby production.
Phylloxera are small, aphid-like insects that are cream-colored and roughly 1/8” in length. The insects hatch after bud break in the spring and quickly begin feeding the tree’s foliage, shoots, and nuts. This feeding activity causes rapid growth of young leaf tissue, which surrounds and encloses the female phylloxera, forming a gall. The female will continue to feed and lay her eggs, which will hatch and continue to develop as they feed within the gall and mature. If you cut open a gall somewhere between mid-April and mid-May, you should be able to find the adult insect or nymphs. In early July, the galls split open and adult asexual phylloxera emerge and lay eggs. These eggs hatch into male and female phylloxera whose sole purpose is to mate and produce a fertilized egg, which will overwinter in the female and hatch the following spring.
Two types of phylloxera- pecan leaf and southern pecan leaf- affect only the leaves and foliage of the trees. It appears the biggest difference between these two species is that the pecan leaf prefers immature trees while the southern pecan leaf prefers mature trees. Either way, both of these species cause galls on pecan leaves which can be unappealing to look at, but ultimately are not economically important unless infestations are severe.
The third type, stem or pecan phylloxera, feeds on the foliage, shoots, and even pecans themselves, resulting in significant amounts of damage. Heavy infestation of the stem phylloxera can weaken twigs, deform shoots and nuts, cause premature nut drop, and damage tree health and production for the following year.
Another major concern is that the galls formed by phylloxera are an alternate host for larvae of the hickory shuckworm. Shuckworm adults will lay eggs in phylloxera galls, causing an increased population of shuckworms in orchards with heavy phylloxera infestations. If you have heavy phylloxera infestation, consider treating trees with Intrepid, Dimilin, or Belt to manage shuckworm.
Depending on the type of phylloxera you have, you may or may not need to do anything to manage them. Pecan leaf and southern pecan leaf varieties will not cause enough damage to justify any control measures unless the infestation is heavy. Stem phylloxera, on the other hand, does benefit from being controlled.
Unfortunately, if you’re already seeing phylloxera galls, you’ve missed the opportunity to control them for this growing season – once the insects are in the galls, insecticides will not affect them. Control measures must be implemented at or just before bud break. If you’re a small orchard or hobby grower, there are no effective methods for controlling this pest. For commercial orchards, consider implementing an imidacloprid or chlorpyrifos spray from bud break until the new growth is around 1” in length. If there is a history of heavy infestation, a second application 10-14 days later might be needed if chlorpyrifos is used.
