Tuesday, June 24, 2014

"Warts" on Pecan Leaves Can Be Galls

Wart-like Pecan leaf galls.          PHOTO/Renae Lemon
Over the past couple of weeks, several county residents have emailed photos and/or brought in examples of infested pecan leaves, concerned that their trees may be diseased.

UGA's publication "Pecan Trees for the Home or Backyard Orchard", by UGA specialists Lenny Wells, Will Hudson, and Jason Brock, explains that disease can interfere with good production of nuts, so it is easy to see why our residents would be concerned. A reduced harvest of delicious pecans would be a great loss!

The good news is that, so far, all of the affected leaves have been infested by galls, rather than disease. In the popped-open gall just above the 5 and 3/4 mark on the ruler in the photo above, one of the culprits is just barely visible, looking somewhat like a little white worm.

The University of Kentucky's publication "Pecan Insects"  offers this information about the leaf gall that is typically caused by an insect called Phylloxera:
"This aphid-like pest produces galls on new pecan growth. Leaves, twigs and nuts may be affected. Phylloxera over winter as eggs in bark crevices. In the spring eggs hatch and the tiny nymphs feed on tender young growth, secreting a substance which stimulates plant tissues to develop into galls. When the nymph matures, eggs are deposited in the gall. Young nymphs develop within the gall. The gall splits in several weeks liberating them. Several generations are produced each year, as long as there is fresh young growth on the tree.
Control is initiated with the use of a dormant oil application. During the growing season, controls should target the "crawler" stage before the galls form. Once the gall is formed the damage is done. The crawler is active just before or at bud-break. Controls initiated after the start of gall formation are not effective."
In other words, it's too late to treat now. Many of the infested leaves will fall, and it could be that nut production will be reduced, but the galls do not always appear on the same tree every year. It may help to clean up fallen leaves as part a control program.

A UGA in Thomas County Ag blog post has this to add about Pecan Phylloxera: "Many beneficial insects like lady bugs, lacewings, and syrphid fly larvae feed on phylloxera and eggs after each generation of galls open."