Which Kanza trees need thinning this year?

    If you are a long time reader of this blog, you may recall that we have been thinning a block of Kanza trees a little bit each year for the past several years. Today, I took advantage of the warm sunshine to walk through our Kanza block and mark trees for removal this winter.
   In some areas of this 3 acre block of trees the canopies of adjacent trees are beginning to almost touch (photo above, right). In these areas, I flagged some trees for removal.

   But just a couple of tree rows away, trees have not grown as fast and adjacent trees still have plenty of room to grow (photo at left). You might be wondering why, in such a relatively small area (3 acres), are our Kanza trees growing at such different rates. The answers is simple--small changes in soil conditions. All the trees in this block are growing in a soil classified as Osage Silty Clay. However, all soil types contain minor variations that can effect tree growth. The fastest growing trees in this block are growing in areas that are slightly more silty. In contrast, the slowest growing trees are found in soil with more clay.

The initial tree spacing for this orchard was 30 feet by 30 feet. We started thinning this grove in 2012. After thinning, the trees are left at a 42 foot by 42 foot spacing (photo at right). As you can see, the canopies of adjacent trees have ample room intercept sunlight and grow new nut bearing wood.
    After walking the grove today, I marked 9 trees for removal this winter. The blog posts listed below will give you the history of our thinning program in this block of Kanza trees.

2012 Making the decision to thin Trees 
2012 Thinning a Kanza Block
2014 Early spring thinning
2015 Time to think about tree thinning 
2015 Sticking to the plan

Yield data from 2015 cultivar trials

    Harvesting pecans from cultivar trials takes a lot of effort. We harvest dozens of plots separately by cultivar, then work to clean and weigh the nuts from each plot. The results, however, are worth the effort. By the end of the harvest season, we have not only harvested thousands of pounds of pecans but we have also collected the data that allows direct yield comparisons between cultivars. In this post, I present the yields from 3 different cultivar blocks

    Our oldest cultivar trail was established in 1981 by planting one-year-old pecan seedlings. Trees were set on a triangular spacing with 35 feet between trees.These trees were grafted starting in 1984. During the winter  of 2008 (after the 2007 ice storm), we thinned the grove by removing every other row. Today these trees stand at a 35 by 60 foot spacing.
    The 2015 yield data for the nine cultivars in this trial is presented in the table at left. The yield per acre values were calculated from the per tree data based the current tree spacing. By far, scab-resistant Major produced the largest crop among these 9 cultivars. Yields from Colby, Dooley, Giles, Hirschi, and Peruque were terrible. The heavy scab pressure we experience in 2015 negatively impacted nut production from these 5 cultivars.
 

     In 1983 we transplanted more seedling trees to establish additional cultivar evaluations. These trees were planted on a 30 ft. by 30 ft. spacing then thinned in 2008 to the current spacing of 42 ft. by 42 ft. In 2015, Osage produced the greatest crop among these 9 cultivars (table at right). This was the "on" year for Osage, a severely alternate bearing cultivar. This past summer we thinned the nut crop on our Lakota trees and still produced an excellent crop. Yields from Giles and Chetopa trees were disappointing, producing less than 1/3 the crop as compared to other cultivars in this trial.  

   The table at left presents the yield data from a trial first established in 1991. This planting was established at a 30 ft. by 30 ft. spacing and is scheduled for thinning this winter. This was the first year Oconee produced a big crop for us. Oconee often ripens late in our area and this was the first time we harvested nuts with fully developed kernels. Caddo, Oswego, and Shepherd were other high yielding cultivars this year.
    In reviewing the results of all our cultivar trials make sure to remember that one year's data should not be used to plan a new massive grafting campaign. I've seen some of these cultivars long enough to know to avoid them (ie. alternate bearing Osage and USDA 64-6-182), while others still make me worry about their late ripening dates (Caddo, Oconee).

Looking inside a swollen lower pecan trunk

I have visited many native pecan groves over the years and have always found at least one tree in each grove that has developed a swollen, disfigured lower-trunk. Trees with this condition are typically weak nut producers and often suffer from significant limb loss. As I work with growers to improve their native groves, I always recommend removing these unhealthy trees.

 The swollen lower trunk condition is most prevalent under two types of growing conditions:  Trees growing under extremely wet soil conditions (photo at right) or pecan trees growing in shallow soils along upland creek bottoms.  In both cases the trees are growing under water stress. I the first case, the tree and its root system is swamped by too much water while the tree growing on the upland site frequently suffers mid-summer drought. Less frequently, trees can develop a swollen lower trunk even when growing in close to ideal soil conditions.

While making plans to thin trees in our native groves this winter, I decided it was time to remove an unhealthy tree with a swollen lower trunk (photo at left).  But I’ve always wondered -- What is going on inside the trunk to make it swell like that? It was time for a closer look.  I started by looking at the bark all around the lower portion of the trunk. The affected tree had several obvious wounds that looked just like old pruning wounds (photo below). However, this tree has not had a limb removed from the lower portion of the trunk for more than 60 years. In that amount of time, an old pruning wound should have completely disappeared. Something else was causing these wounds in the bark. With further inspection of the lower trunk, I also found a nectria canker and a phomopsis gall (photo below).

Wounds visible in the bark of a swollen trunk

Nectria canker on the left and Phomopsis gall on the right

By looking at the bark of the tree, I could tell that several pathogens were infecting the lower portion of this tree’s trunk. However, I really wanted to find out what was going on inside this tree’s trunk to cause the trunk to swell.  I used my chainsaw to cut a section out of the lower trunk area so I could look at patterns of wood growth (photo at right). The piece of wood I cut from the tree extended from just above the point of swelling downwards towards the soil surface. Once I removed the trunk segment from the tree, I took the wood into my shop and sanded the vertical face perfectly smooth to reveal the wood grain (photo below).

Before I show you some of the wood deformities I found inside this tree, I think it is important to show you what normal wood growth looks like when cut longitudinally. Thephoto at right shows a section of pecan wood with a normal wood growth pattern. The annual growth rings, so easily recognized when a pecan tree is cut in cross-section, are a little harder to see this longitudinal slice through the wood. However, you should be able to see the alternating pattern of large-pore, spring wood and finer textured summer wood that provides a visual record of annual cycle of wood growth.

Towards the upper portion of the wood sample, I found what can generically be called a wood burl (photo at left). Growing outwards from a bark inclusion (the black crevasse in the wood) you can see deformed wood growth that almost appears like it is bubbling outwards towards the surface of the outer bark. Lower down on the trunk segment, I found multiple burls both near the surface and deep inside the wood (photo below). In every case, the deformed pattern of wood growth seems to have originated with a wound in the wood.     

After cutting into this tree, it is clear that trunk swelling at the base of pecan trees is due in large part to the development of burl wood. Burls can form in response to either fungal or bacterial infections but how these organisms penetrated the tree trunk is the real key to understanding lower trunk swelling. Each burl was formed in association with an injury in the wood. These injuries were most likely created sometime in the past by the feeding of wood boring insects. Trees that grow under stress (too much or too little water) seem to attract both dogwood borers and flat-headed apple tree borers. The movement of these insects in and out of the tree’s trunk most likely spread the pathogens responsible for burl formation and ultimately leads to swelling of the lower trunk.

Pecan cultivar yields: The impact of pecan scab

    During an average year, we receive about 40 inches of rain at the Pecan Experiment Field. During 2015, more than 65 inches fell on our pecan groves. With all that rain, we experienced a severe outbreak of pecan scab. During the summer, we made three applications of fungicides to slow the spread of scab but found that some cultivars still became covered by the disease (photo at right).
  In previous posts made during the 2015 growing season, I addressed the impact of scab on nut size and kernel fill and even photographed a couple of cultivars completely destroyed by scab.
    This week we finally finished cleaning and weighing the nuts harvested from one of our pecan cultivar trials. After reviewing the 2015 data (table below), I was struck by the observation that the lowest yielding cultivars in the trial were also the cultivars with the least amount of scab resistance.

    In the table, I've listed yield as yield per acre. In the field there are 16 trees of each cultivar in this trial representing 1/3 of an acre of trees. The scab rating listed is a multi-year average for each cultivar that can be used to judge the relative susceptibility of a cultivar to scab infection. A rating of "1" means total scab resistance while nuts completed covered by scab receive a rating of "5".
    Scab resistant Kanza trees produced almost 3 times as many nuts as scab susceptible Chetopa and Giles trees this past growing season. Our fungicide program reduced but did not eliminate scab infections on Chetopa and Giles in 2015. After looking at the nuts blown out of the cleaner, I can report that scab definitely reduced kernel fill on these scab susceptible cultivars. More nuts in the cleaning pile means less marketable nuts to report as total yield.
    Not all scab resistant cultivars produced outstanding yields. Norton, an old northern pecan cultivar, is scab resistant but is not a prolific nut producer. Stuart has only moderate scab resistance but produced an excellent crop in 2015. All in all, it looks like I'll be grafting more Kanza next spring. 

Native pecan yields drop in 2015

    The 2015 native pecan crop at the Pecan Experiment Field was a little disappointing. For 35 years, we have been recording the yield from 6 plots of native pecan trees and this past season, our native trees produced a below-average crop. The 2015 native crop came in at 825 lbs./acre as compared to our long-term average yield of 1156 lbs./acre. The yield history of our native plots is given in the chart below.
     If you study the chart for a bit, you'll see that there is no obvious pattern to yield variation from year to year. Record low yield in 1990, followed a winter when temperatures dropped to -26 F in mid- December causing serious shoot damage. The Easter freeze of 2007 destroyed emerging shoots and limited pistillate flower production. And finally, the December 2007 ice storm caused massive limb loss negatively impacting yield for following two growing seasons. Besides these three major weather events, I'm sure that natural variation in weather patterns have a lot to do with how trees perform over time. Unfortunately, all we can do about the weather is complain about it.
 

Kanza nut yield for 2015

    Kanza has become one of the most popular cultivars across many northern pecan states. Back in 1995, we established a three-acre block of Kanza trees and I'm sure glad we did. In 2015, the trees in this block produced a great crop of nuts (photo at left). 

    Just before shaking and nut harvest you could see the the 2015 Kanza crop was going to be a good one. The trees produced nuts throughout each tree's canopy (photo at left).

     After cleaning our Kanza crop and weighing the nuts, we learned just how well these trees performed. Twenty years after starting a new orchard from seed and grafting the resulting seedlings to Kanza, we harvested over 1500 lbs. of pecans per acre (Table below).
    In looking over the table let me point out a few things. First off, you can see how drought during 2011 and 2012 impacted both total yield and average nut weight.  With the return of normal rainfall starting in 2013, nut yield steadily increased during the period of 2013-2015. This increase in yield occurred even as we removed trees using our gradual thinning plan. When the first thinning is complete, we will have removed 72 trees within the three acre block.