What are the knots or balls that form on the leaves and stems of my pecan tree in the spring? Will they harm the tree?

Michael J. Hall, Bollich, Patricia A.  |  11/9/2006 11:03:36 PM

The knots or balls that you see on your pecan tree in the spring are not caused by a disease but are actually galls formed by a near microscopic-sized, aphid-like insect known as pecan phylloxera. When infestations of this insect are severe, defoliation, nut loss and twig die-back can occur. Infestations of pecan phylloxera will not kill the tree. Pecan phylloxera eggs hatch in the spring at the time the buds begin to open. The immature nymphs that hatch from the eggs move to the opening buds where they settle and begin to feed. As the nymphs feed, a gall begins to form around the insect, eventually enclosing it within. Infestations of this extremely small insect often go unnoticed until the galls have formed. Once the phylloxera is enclosed within the gall, control is no longer possible. Some common pecan cultivars susceptible to pecan phylloxera include Desirable, Schley, Stuart and Success.

More detailed information on the distribution, description, life cycle, damage, and control of pecan phylloxera can be found on the Pecan Phylloxera fact sheet and on the Louisiana Recommendations for Control of Pecan Insects in Commercial Pecan Orchards guide on the Entomology page of the Pecan Station Web site. 

Question answered by Dr. Mike Hall, Pecan Research-Extension Station entomologist.

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