Wednesday, February 22, 2012

Thinning a Kanza block

In a previous post, I talked about making the decision to thin trees in a block of Kanza pecan trees. To help make the decision on which trees to remove, I spent some time plotting out a tree size map using the diameter of every trunk in our Kanza block. Since crown size is proportional to trunk diameter for open grown trees, I can create a visual representation of the orchard using plotting features in Microsoft Excel (plot at right).
Looking over the map, you can see that the orchard has begun to crowd in the northeast corner (upper right). See how the tree circles on the graph are touching each other in that portion of the field.  This is exactly what we see in the field--limbs starting to touch only in a small section of the orchard. You will also note that we have a few small trees scattered through the orchard that seem to be lagging behind the others.

Using this visual information, I decided on the best pattern for thinning the entire orchard. For the first thinning, we will remove trees on the diagonal. The map at left shows the diagonal tree rows that will be removed (red lines). With this thinning plan I will remove all but one of the runty trees.
The entire orchard does not need to be thinned at this time. We will remove trees only in areas where the trees are beginning to crowd. For this first year of thinning, we plan to remove just 7 trees. These trees are marked on the map by black dots.
Thinning this orchard will take several years, but we’ve got a plan in place. As trees in other portions of the orchard start to crowd more trees will be removed until eventually the entire orchard has been thinned.
We cut down the 7 trees marked in our thinning plan today (photo at right). Once the trees are on the ground, we pull the entire tree top out of the orchard using a tractor and log chain. These trees will eventually be cut up for firewood.

Cutting down trees gave me the opportunity to see the growth rate of trees in this block of Kanza trees. In the photo at left, you can see  annual growth rings of 1/4 to 3/8 of an inch per year every year. This tree was growing fast! It no wonder we needed to start the thinning process in this portion of the orchard.

Tuesday, February 21, 2012

Winter buds: Pecan and hickories

The terminal of a pecan twig
      Ever take a close look at pecan buds in winter. You can learn a lot about trees just by observing how buds are arranged on the twig. In the photo at left, you can see the terminal bud and several lateral buds of a pecan stem. Note that the terminal bud looks much different than all the lateral buds. The terminal bud looks like a collection of tightly compressed leaves formed into the shape of praying hands. It is from this bud that the pistillate flowers will emerge this coming spring. The lateral buds are tear-drop shaped and are completely covered by a protective scale.  Within each of these lateral buds is a vegetative bud flanked by catkins on each side. You can see how these lateral buds develop in the spring here.

Primary, secondary, and tertiary lateral buds
     There is one more interesting bud feature on pecan trees.  You will find at least 3 buds at each node. In the photo at right, you can see 3 buds lined up above the leaf scar. The large bud on the top is the primary bud. Underneath are secondary and tertiary buds that are formed to provide reserve growing points in case the primary bud is lost to mechanical injury or frost.  We discovered the importance of secondary buds when almost all primary buds were killed during the Easter freeze of 2007.

Terminal buds of four members of the hickory family
    Now that we've looked at pecan buds, I thought it would be interesting to see how pecan compares to other members of the hickory family (photo at right).  Within the hickory family there are 2 major groups: the pecan hickories and the true hickories. The pecan hickories are represented in the photo by pecan (of course) and bitternut hickory. These hickories have "valvate" terminal buds (the praying hands). Bitternut hickory is easily identified in the field by its bright, rusty-orange buds.  The true hickories have scaly buds are are represented in the photo by the shellbark and shagbark hickories. Also note the immense size of the terminal buds of the true hickories.
Buds of a pecan, shellbark hickory, and its hybrid (hican)
     While we are looking at photos of buds, lets look at a naturally occurring hybrid hickory commonly called a "hican".  In the photo at right, you can see the buds of a pecan, a shellbark hickory, the the cross of these two species (the hican). Note that the terminal bud of the hican is not as scaly as the true hickory but it doesn't look anything like a pecan terminal bud. It seems when these two species cross, the progeny seem to favor the true hickory side of the family.

Friday, February 17, 2012

Identifying pecan trunk injuries

     Today, I enjoyed a late winter walk through our native pecan grove.  In the bright sunshine and without a canopy of leaves, the immense size of pecan trees really struck me.  Many trees are now over 3 feet in diameter and over 100 years old (photo at left).
     As I walked around, I was able to spot some common problems associated with tree trunks. Many of these problems are man-made, the result of pruning trees or mowing the ground cover. Let's take a look.

   A healthy trunk is straight with flared roots at the very base of the tree (photo above). The tree trunk at right has a swollen base that features rough, pebbled bark. This type of trunk is the result of an infestation of wood boring insects that attack a tree already under stress.   The stress is usually water related--either too little water (shallow soils) or too much flooding (high water table). You can tell this tree is in trouble when you look at the tree's crown (photo below).

      The canopy of the tree with a swollen base has several dead limbs and has very narrow crown (photo at left). This tree is not crowded by adjacent trees, it is just simply a tree in decline.  If you are planning a tree thinning operation in your grove, this type of tree should be among the first to be removed.

   Here's an all-too-common trunk problem that I like to call mower blight (photo at right). If you hit a tree trunk with a mower and pop off the bark, you have opened up the tree to wood rotting fungi. The kind of wood rot pictured here took years to develop yet the tree has remained productive. However, there will come a time when advancing decay will make this tree subject to wind throw.  Pecan trees seem to tolerate a lot of abuse but its best to avoid hitting trees with farm equipment.

      A lopsided trunk (photo at left) is usually associated with an old pruning wound. Forty years ago this was a forked tree. At that time, one of the forks was removed to encourage the development of a single trunk.  This tree must have had two fairly large forks at the time of pruning because the crease in the side of the tree is a remnant of the old pruning wound.   However, it seems the pruning was done correctly (pruned on a slant) and the trees remains healthy.

    If the pruning cut to remove a fork in a tree is not preformed correctly,  massive wood rot can occur. Here's an example of a tree fork that was removed with a horizontal cut (photo at right).
The flat surface of the pruning wound held moisture from rainfall and accelerated the rate of fungal wood rot. At this point, the decomposition  of the wood is so advanced that it is proving a place for weeds to grow. Cutting a forked tree to one trunk is a good idea, but the way you make the cut is critical for preserving tree trunk health. 


Friday, February 10, 2012

Cutting pecan scionwood

  Starting in mid-February, we take advantage of every nice-weather day to cut pecan scionwood in preparation for this spring's grafting season. We cut dormant scions from last year's new shoot growth. The best scions are cut from long vigorous shoots that are produced by young trees. In the photo above, I've taken a 2 foot long shoot and cut it into 8 inch long scions. While cutting up the shoot, I laid the scions down in order from the basal scion (top)  to the shoot terminal (bottom).
    There are a few things you should notice about these scions. First, note that buds are farther apart on scions cut near the base of the shoot. Also, the closer I cut to the terminal of the shoot, the more the scions take on a zig-zag shape. The best scions for grafting are relatively straight and have widely spaced buds.
    The second thing to notice is that bud size seems to increase as you move up the shoot. This occurs as a function of shoot apical dominance. During the summer, the growing point at the top of the shoot actually inhibits the growth of buds near the base of the shoot.    Bud size on a scion is not important to grafting success as long as buds are viable and firmly attached.  Because of the apical dominance effect, basal scions are prone to losing primary buds and should be checked for bud viability.
    The top 3 scions would be my choice for grafting. These sticks are relatively straight and have enough wood diameter to ensure grafting success. The 4th stick from the top could be used in a pinch but I would discard the bottom 2 sticks for being too small in diameter and too crooked in shape.

Wednesday, February 1, 2012

Pawnee vs. Lakota

    I have been a fan of the Lakota pecan cultivar for a long time now and have often described it as a scab free version of the Pawnee cultivar.  These two pecan cultivars share a lot of traits. Both Pawnee and Lakota are precocious, productive, and fall into alternate bearing if not carefully managed. The nuts of both cultivars are large, thin shelled, and have good oil content.
    There are some major differences between Lakota and Pawnee. Lakota is resistant to pecan scab and ice storm breakage, while Pawnee is susceptible to both.  Pawnee ripens more than 2 weeks earlier than Lakota.
   Looking at Pawnee and Lakota nuts side by side you can see obvious differences in nut shape (photo above). Pawnee nuts are a little bit flattened while Lakota nuts are nearly round in cross section. Both nuts have a distinctive yet different apex shape while Lakota tends to have a tapered base.

    I cracked out some nuts to show how each cultivar and their nut shape influences kernels appearance and quality (photo above).  Note that kernel shape mimics the shape of the shell. Pawnee kernels are broad and blocky,  while Lakota are more narrow and tapered.  When it comes to kernel appearance, note that Pawnee has some problems. Pawnee kernels always seem to be covered fine black speckles that can give the kernel a grayish cast.  And in some years (like this year), the kernels can even have large brown blotches. In contrast, Lakota always seems to produce smooth, golden kernels. I guess that's one more reason to like Lakota.