Saturday, September 7, 2013

Flat headed apple tree borers make a mess.

   I was mowing the other day when I spotted what looked like a long steak of mold growing on the bark of one of my young pecan trees (photo at right). Oh no! Is this something new I need to worry about? Am I going to lose this beautiful, well-shaped tree? I finished mowing, put up the tractor, then came back for a closer look.

   Upon closer inspection, I found several trees with prominent stains on the bark,  usually centered around the upper side of a branch connection (photo at left). The stain appeared water soaked (dark brown) on the outer margins and fuzzy light-grey near the center. It definitely looked like I had an actively growing fungus on the surface of the bark.
   It all became clear when I looked at the other side of the tree and found a neat pile of insect frass in the crotch of the tree (see red arrow, photo at right). Now I know whats going on here. I don't have a strange new disease on my trees I simply have some actively working flat-headed apple tree borers.
   These common wood boring insects are often found in young pecan trees, especially in orchards that have yet to receive regular applications of insecticides aimed at controlling nut feeding pests. However, the staining on the outside of the bark is not normally associated with apple tree borers.
   The stains are a result excessive sap flow that occurred in response to the heavy rains we experienced from July 21 to August 12 (> 15 inches). Sap flowed into the wood borer's tunnel then spilled out onto bark surrounding the branch crotch. Since tree sap contains several forms of carbohydrates, the sap-soaked bark combined damp weather conditions provided an excellent environment for the growth of the common grey mold fungus.
    Since mid-August, the weather has turned off hot and dry. No new sap is flowing from wood borer tunnels and the grey mold fungus has stopped growing. However, the stains have remained and will remain until winter rains scrub the bark clean.
   One final note. Apple tree borers do only slight damage to the tree and rarely require chemical control.