Friday, May 18, 2012

Galls on pecan stems

   This spring has provided excellent conditions for the development of galls created by pecan stem phylloxera (photo above). Pecan growers in Kansas, Missouri, and Kentucky are all finding trees covered with stem galls. The scientific name for this insect is Phylloxera devasatrix and like the name implies, this phylloxera species can have a devastating effect--distorting pecan tree growth and eliminating nut production.

    If you open the galls at this time of year you will find it filled with hundred of winged aphid-like insects (photo at left). When the gall cracks open, the winged phylloxerans will fly out, mate, then mated females will find a hiding place in the rough bark of the tree.  While hidden in the bark the female's body will become filled with eggs that will remain dormant until budbreak the following year.
    At budbreak the eggs hatch and "stem mothers" crawl out to the emerging pecan buds. Once she finds green tissue,  a stem mother begins to feed on plant sap, secreting a compound that caused the tree to grown a gall over the insect. After the gall is formed stem mothers lay eggs inside their galls. These eggs hatched into the winged form of the insect.
    To control phylloxera an insecticide needs to be applied at the outer scale split stage of nut development (photo at right). The insecticide is aimed at controlling crawlers before they become imbedded inside a gall.
    If you see a tree infested with pecan stem phylloxera, mark that tree now. Next spring, spray only the marked trees.
    The pecan leaf phylloxera is a related species that creates galls on pecan leaf blades. The control timing for pecan leaf phylloxera is at leaf burst; so make sure you identify which species is attacking your trees before planning insecticide treatments for next spring.