Orchard thinning yields great scionwood.

    February is a good month for thinning pecan orchards. It is also a good month for collecting pecan scionwood. So today, we took advantage of the sunny weather to collect scions from the trees we cut during a orchard thinning operation (photo at right).

   Once a tree is cut down, you can ready see why it is so hard to find good scions from nut bearing trees. On lower and mid-canopy limbs, new shoot growth is limited by nut production. The photo at left shows a typical lower-canopy branch. Last year's growth is highlighted by the yellow line and extends about 5 inches before terminating in a peduncle or the former fruit bearing stalk. Note that last year's shoot growth is lighter in color and displays large, prominent buds. However, this shoot does not make for very good scionwood. The growth is short, the buds are close together, and the stem is crooked. 

    Walking around to the top of the tree, I found really long, healthy shoots that would make great scions (photo at right). What was once 40 feet up at the very top of the tree, was now easily accessible from the ground.

   I cut dozens of one-year-old shoots that measured nearly 3 feet in length (photo at right). This is the perfect type of wood for cutting into scions. 

    Taking the 34 inch shoot pictured above, I cut the wood into pieces. In the photo at left, I've arranged the wood from the lowest portion of the stem to the terminal. In looking over these pieces of wood, notice how bud size increases and buds become closer together as you get closer to the terminal. For great scionwood, you want prominent, healthy buds, but those buds should be widely spaced to make grafting cuts easier.
    I always discard the terminal portion of the shoot when collecting scionwood. The terminal is crooked, has too many buds, and is nearly impossible to carve when grafting.
  On the other end of the shoot, the basal piece of wood has very small buds which are prone to falling off the stem (yellow arrow points to aborted bud scar). I'll save this piece of wood for grafting because the secondary buds can grow into new shoots. However, when I'm out grafting and have a pile of scions to choose from, I'll choose this type of wood only after I've run out of scions with more robust buds.

Thinning trees from a Kanza block

    In keeping with our plan to gradually thin our block of Kanza trees, I cut down nine trees yesterday (photo at right).  We started thinning this block of 144 trees back in 2012, removing 5 to 9 trees each year since that time. So far we have removed a total of 34 trees in 5 years time.

    The map at left shows the position of the trees we removed in 2016. Each green circle represents a tree with the diameter of the circle proportional the the diameter of the tree. The black circles represent trees removed this week.
    So far I've been pleased this this progressive approach to orchard thinning. By removing just a few trees each year we have been able to prevent orchard overcrowding while maintaining total orchard yield. You can review the yield and tree removal history of this block of Kanza trees in this post:

Kanza nut yield for 2015

Making pecan breeding plot selections

     To many pecan growers, thinning a pecan orchard is the hardest job they will ever have to accomplish. Cutting down trees that required so many years of work to grow seems heartbreaking. But over the weekend, I started thinning trees in our pecan breeding plot (photo above). This is more than just a simple tree thinning operation. I was making tree by tree decisions of which trees were worth saving and which would be eliminated from the breeding project.

    Many trees in the breeding plot have now produced nuts for three years giving us a good idea about nut size and percent kernel for each tree. As you would expect, the nuts produced by a field of seedling trees varies widely. The photo above shows nuts produced by three trees in our breeding plot. The nut at the far left weighed 8.17g and yielded 58.61% kernel. This is one tree I definitely needed to save. The football shaped nut in the center produced a very attractive but small kernel. However, at only 4.54g and 47.29% kernel, I choose to cut down this tree. At the far right, this small 4.99g nut had a thin shell (53.67% kernel) but the nut was way to small to remain in the trial.

    Not all tree removal decisions were based solely on nut size and percent kernel. I choose to remove trees that produced kernels with serious defects and trees that exhibited severe susceptibility to pecan scab. The photo above illustrates one kind of kernel defect that warrants tree removal. The nut on the right is marked with very unattractive dark brown mottles. Compared to the bright straw-colored kernel at left, it is easy to see which nut would be attractive to consumers (left nut) and which tree needed to be removed (right nut).

Pecan cultivars and tree size

    In setting out a new pecan cultivar trial, I anxiously wait for the trees to start bearing so I can record nut production data. Nut size, percent kernel, flowering type, maturity date, yield, and disease resistance are all among the key cultivar attributes that can define cultivar success. However, not all cultivar characteristics are revealed within the first decade of nut bearing.
    I was walking through the oldest cultivar trial on the research station when  I noticed obvious cultivar differences in over-all tree size. In the photo above, you can see that Major produced a much larger tree than Dooley. Both cultivars were grafted onto Giles seedling rootstock planted in the field back in 1981. The only difference between these two trees is the scion cultivar. 

    Looking around this 35-year-old trial, I found that trunk diameter was largely a function of cultivar. To create a visual record of cultivar differences in trunk diameter, I photographed the trunks of 6 pecan cultivars placing a one-foot-long ruler across the truck for scale (photo above ). Major and Peruque grew trees so large they seem to dwarf all others in comparision. Colby and Posey grew moderate sized trees while trees grafted to Giles or Dooley seemed small in comparison.
   I would never consider tree size a very important tree characteristic in making cultivar decisions. However, tree growth rate becomes important when planning initial orchard spacing and making subsequent thinning decisions. Large growing trees, like Major or Peruque, should be established at a wider spacing--let say, 40 feet rather than the standard 35 feet. Tree growth rate will also influence tree thinning decisions. The larger a tree grows, the sooner you will need to thin out adjacent trees to make room for future growth.
    It takes at least 30 years of cultivar testing to make accurate tree size determinations. In that time, many cultivars will prove unworthy of future propagation. Of the six cultivars pictured above, I would consider grafting only Major because of its scab resistance and regular nut production. But now, when I graft new Major trees, I'll also be sure to allow more space for these trees to grow.