Thursday, June 23, 2016

Galls on seedling pecan trees

   I was trimming up some young trees when I came across a seedling tree that had leaves sprinkled with light green galls (photo at right). These galls are formed by the plant in response to the feeding of an insect called the pecan leaf phylloxera. I find leaf phylloxera most commonly on juvenile pecan trees that have not yet been grafted.

    I photographed a couple of leaf phylloxera galls on the upper side of the leaf blade then flipped the leaflet over so you can see the same galls from the under side (photo at left). On the upper leaf surface the galls a raised, irregular-shaped and smooth. On the lower side of the leaf, the galls are raised with a nipple-like projection in the center of the gall.  
     I cut open one of the galls, then photographed both halves (photo at right). The gall was filled with aphid-like insects. I found both winged adults, and wingless nymphs inside the gall. These small insects feed on pecan plant tissues that make up wall of the gall.

  Eventually the gall splits open on the underside of the leaf allowing winged adults to leave the gall (photo at left). After winged adults mate,  female phylloxerans will find a secluded spot in the rough bark of the tree to over winter.
   I usually don't bother trying to control these insects on juvenile pecan trees. Once I graft the tree, the problem seems to disappear.