Mature pecan tree pruning mistakes

    Every time you mow a pecan grove it seems like there is a limb just low enough to knock your hat off and into the brush hog. After you lose enough hats, it becomes clear that some lower limbs need to be pruned. We rarely prune mature pecan trees but when it comes time to get out the chainsaw, making the proper cuts will prevent future problems.
    The other day I spotted a mature tree that features two of the most common pruning errors. The red arrow points to a branch stub. In this case, a limb was pruned off about 8 inches out from the branch collar. The branch collar appears where the limb connects to the trunk and is the natural location for a tree to grow over a pruning wound. In the photo you can see that the branch stub is rotting away, while the tree has developed an exaggerated branch collar in a attempt to seal over the wound. If this branch had been pruned correctly (at the branch collar), the tree would have sealed the wound by now. However, the rotting branch stub prevents proper wound healing and allows wood rotting fungi to penetrate into the heart of the trunk. Rule #1: don't leave branch stubs when pruning.
   The yellow arrow points to a lower limb that has been pruned back at several points but still extends 10-12 feet from the trunk. This limb is now dead and starting to decay (note missing bark on limb near trunk). Hacking back a lower limb places the entire remaining portion in the shade of upper limbs. Pecan is shade intolerant; so if a limb does not received enough sunlight, the tree aborts the limb. The best course of action is to remove lower limbs completely, pruning the limb all the way back to the trunk and just outside the branch collar. If not pruned off, the limb shown in the photo above will probably end up being shaken off during harvest (just hope it doesn't break something when it falls). Rule #2: prune lower limbs back to the point they are attached to another limb or the trunk.

Bark grafting

   When you live in an area were native pecan trees are plentiful, young trees seem to pop up everywhere. This is the case on my farm. I've been mowing around volunteer trees allowing them to grow to a point where I don't need to bend over to graft them (I can graft much faster standing up). I  let the seedling trees grow 5 to 10 feet tall (1.5 to 2 inches in diameter) before using a bark graft to establish my chosen cultivar. There are several variations in bark grafting but I've become comfortable making my version of the modified rind graft.

    All bark grafting methods are similar. The scion is inserted between between the bark and wood on one side of the stock. The key to successful bark grafting is to make certain that cambium on the scion is placed in direct contact with cambium of the stock.

    To start the modified rind graft, cut off at least 1/2 of the stock leaving a stump less that 4 inches in diameter (for faster healing I prefer trees in the 1.5 to 2.5 inch diameter range) (photo at left). 

     Next, inspect the stump and look for the "flat" side of the stem. On the flat side, make a downward incision with your knife cutting trough the bark around 3 inches long.(photo at left)

   Now it is time to carve the scion into a shape that will fit under the bark and maximize cambial contact. I start by making a deep cut, removing about 2/3rds the thickness of the scion, This cut is about 2.5 inches long and features a pronounced shoulder at the top of the cut.(photo above)

   I turn the scion over and make a shallow cut into the wood of the back side of the deep cut. This cut is not made parallel to the deep cut but angled to one side. When finished, I have a thin piece of bark adjacent to the deep cut on one side and a much thicker strip on the other. The cut on the back side of the scion should start just below the shoulder of the deep cut and should give the scion a wedge shape when completed. (photo above)

     Next I make a third cut perpendicular to the deep cut along the thick bark strip edge(photo left). I make this cut  just deep enough to expose the cambium and I make certain to leave a strip of bark between the backside cut and the perpendicular cut. At this point my scion has triangular shape in cross section.  I complete scion preparation by making a chisel point on the end of the bud stick (photo above). This final cut should be made on back side of the scion. 

 

   Now I'm ready to insert the scion into the stock. I use my grafting knife to gently pull the stock’s bark away from the wood on the left side of the bark slit. Inserting the scion between the bark and the wood of the stock, I tap the scion down into the stock until the shoulder of the deep cut fits snugly against the upper side of the stock.  The deep cut should be facing the wood, while the shallow cut should be covered by the raised bark flap and perpendicular cut should fit snugly against the bark slit. (photo at left)

    I secure the graft union with staples (use a 5/16 staple from a light duty staple gun such as Arrow model JT21). It is important  staple down the bark firmly against the scion and to be sure that all air pockets are removed. (Photo at left)

    Like all the grafting methods I use,  I cover the graft union with aluminum foil and a plastic bag. And finally,  I attach a bird perch stick to the stock with black electrical tape  to prevent the birds from breaking out the scion. (photo at left)
    See related posts on maintaining a bark graft one year after grafting and the anatomy of a successful bark graft. 

Spray drift injury

   Last week a local farmer had several hundred acres of crop land sprayed for weed control in preparation for planting no-till soybeans. A farm services company applied a mixture of Round-up and 2,4-D for a quick knock down of all weeds. Unfortunately, the applicator made a huge error in judgement. The herbicides were applied on a day that had both high winds and high temperatures--perfect conditions to maximize spray drift and 2,4-D vaporization.

   The wind carried the 2,4-D more than a mile from the spray site causing massive damage to native pecan trees. Phenoxy herbicide damage to pecan is easily recognized by the curling of new growth and yellowing of foliage (photo at above). As the season progresses the trees will become either partially or totally defoliated. The nut crop will abort.
   From past experience with 2,4-D damage, the trees that survive will take at least 3 years to recover. We are currently working with the Kansas Department of Agriculture to document this terrible event.

Pollination season

   Pecan pollen is starting to shed and pistillate flowers are in full view. In the photo at right, you can see a cluster of female pecan flowers growing a the tip of a new shoot. Female flowers are not very showy.  You can see the reddish stigmatal surface sitting on top of four leafy bracks. Below the bracks is the ovary. There are four female flowers in this cluster.
    The reddish color and presence of stigmatal fluid indicates this cluster of pistillate flowers is ready to receive wind blown pollen. The stigmas of pecan pistillate flowers can range in color from green to orange to deep red.

   The male flowers or catkins of pecan are also ripening and starting to shed pollen. In the photo at right, you will note that the catkins are actually made up of a long series of sack-like structures held under a leafy bracts. As the catkins mature, the pollen sacks grow larger and start to take on a yellowish color. During periods of low humidity, fully mature pollen sacks burst open releasing millions of pollen grains into the air. The pollen is transferred by wind to the receptive stigmas of pistillate flowers.
    Once all the pollen is shed, catkins turn brown and fall from the tree.