Pecan bark peeling?

'Hark' pecan bark

   I was collecting wood from our scionwood orchard and noticed the unique bark appearance of the Hark pecan cultivar (photo at right). Young trees (roughly 6" in diameter) of this cultivar have very distinctive exfoliating bark. The peeling bark on this tree does not represent some dreaded disease but is simply the natural way this tree's bark reacts to diameter growth. The long strips of curled-up bark reminds me of the bark of a shagbark hickory.
    Bark appearance is controlled both genetically and by the growth rate of the tree. A fast growth rate serves only to exaggerate any form of bark exfoliation. If you look carefully at the bark of different pecan cultivars, you will soon notice distinct patterns of appearance. Let me show you a few examples.

'Major' pecan bark

    Major trees produce a scaly bark that seems flake off in small square patches (photo at left). This distinctive 'Major' bark pattern makes field identification of this cultivar easy at anytime of the year.

'Hirschi' pecan bark

    The bark of Hirschi also appears to crack in square patches (photo at right) but it does not take on the scaly appearance found with Major trees . This bark pattern is not terribly unique among pecan cultivars so it is difficult to identify Hirschi by bark appearance alone.

'Giles' pecan bark

 

   Giles trees have a more furrowed bark appearance (Photo at right). The look is mostly non-descript and gives no clue as to the cultivar.  The bark simply looks like bark should look.
     There are many cultivar characteristics that can be used to identify a pecan cultivar. Bark appearance is cultivar specific but only some pecan cultivars produce bark so distinctive that it sets them apart from other cultivars. 

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.

Pecan bark flaking off?

Kanza Bark

    The other day a pecan grower expressed his concern about the cultivar, Kanza. "It looks like Kanza is susceptible to sun scald. The bark is flaking off". Well the bark looks like it is flaking off (photo at right) but the sun has nothing to do with it. Kanza, like its Major parent, has bark that exfoliates in blocky patches.
    When trees grow in diameter the older (and outer) bark can not stretch to cover the increased girth. As a consequence the outer bark cracks. The shape and pattern of these cracks are genetically controlled and do not indicate any inherited weakness.
    There is huge variation in bark appearance among pecan trees. Growing behind my office are three seeding trees, all the same age and roughly the same diameter. All three trees are in perfect health. Bark appearance among these trees ranges from furrowed to shaggy (Photos below).