Kanza, stick-tights and crop load regulation

  Kanza has become a very popular pecan cultivar because no matter the weather, Kanza always seems to produce a quality kernel (photo at right). Over the past four years, I've been watching our Kanza trees closely and I think I've  discovered one of the ways these trees preserve kernel quality even when faced with stressful weather conditions.  It looks like Kanza trees self thin a portion of their nuts to ensure full kernel filling for the rest of the crop.

    We recently harvested a block of Kanza trees and had dumped a load of nuts into the pecan cleaner. When I looked at the nuts swept up by the harvester, I noticed a large number of stick-tights. The photo at left shows an example of field run Kanza nuts before cleaning. There were plenty of good Kanza nuts mixed in with a few sticks, leaves, and dirt clods. But what stands out are the nuts trapped in blackened shucks.
   It turns out that about 12% of Kanza nuts collected by the harvester this year were stick-tights. Just looking at the photo it seems like the percentage should be higher but a nut stuck in the shuck takes up a lot more space than a nut out of the shuck. 

   I separated out several of the stick-tight pecans, peeled the shuck off, and cracked open the nuts. In every case, I found a brown, paper-thin kernel inside. It looks like each of these stick-tight pecans stopped kernel development at the water stage leaving only the seed coat inside the shell.
   The question becomes--"Why did these nuts stop developing during the water stage?".  During the summer of 2014, we experienced an extended period of dry weather that started during the final stages of nut sizing and continued until late August. In addition, our Kanza trees had set an above-average crop. Most pecan cultivars react to these circumstances by aborting a portion of their crop in what is commonly known as a water stage drop. Nuts dropped in mid-summer often disappear by harvest as they decompose in the ground cover.
   Kanza is different. A Kanza tree stressed by drought and crop load turns off the nut development process during water stage for a portion of the crop but those nuts remain on the tree until harvest. 
   The good news is that Kanza seems to do an excellent job of regulating its crop load to ensure that fully ripe nuts are well filled. The bad news is that cleaning the Kanza crop following a mid summer drought will take a little more time to remove numerous stick-tights. 

Pickin' pecans

Harvesting Pawnee pecans

Shaking a Pawnee pecan tree

     What a great day for harvesting pecans. The weather was warm and sunny and all our harvest machines were operating perfectly (see photos). Unfortunately, the weatherman has forecast  a massive cold wave to push through the Midwest starting tonight. If we don't get much rain overnight, we'll be back to harvesting the rest of this week. But with high temperatures predicted to be only in the 30's (F), we'll need to break out the coveralls, warm hats and gloves and try to stay warm. It won't be as fun as it was today, but we need to beat the squirrels, crows, and deer to our nut crop.

Without a kernel inside, pecan shucks don't open.

    The Kanza cluster, pictured at right, contained four pecans. Three nuts had wide open shucks with pecans ready to fall from the tree. The fourth nut had a shuck that was still tightly closed and showed no sign of splitting open. In a previous post, I mentioned that a pecan weevil infestation can cause the shuck to remained firmly attached to the nut. However, in this case, there was no indication of weevil activity. Was this one nut just slow to open up or had something gone wrong inside the nut?   

   In the photo at left, you can clearly see that three nuts had normally split shucks while the fourth was still bound inside a closed shuck. The nuts emerging from split-open shucks had developed their normal shell color and were packed with kernel (note nuts cut in cross-section at the bottom of the photo).
    It took a little effort, but I could force the tightly held shuck off  the fourth nut. The shell inside had not yet developed normal shell color and I found a paper thin remnant of a pecan kernel inside.
   Back in August, the development of  kernel inside the stick-tight nut stopped during the water stage and a normal kernel never developed. Without a developing seed inside the shell, ripening hormones are not produced in the fall and the shuck does not open.

   

Hard freeze helps open pecan shucks

   On the first day of November, we had the first hard freeze of the season as temperatures dropped to 23 degrees. What always amazes me about the first hard freeze of the season is how quickly pecan shucks open up once all green shuck tissue is killed by cold temperatures. This year, I was able to photograph some pecan clusters two days before the freeze then again two days after the freeze.

   The first cultivar I looked at was Kanza. In the photo above, the Kanza nuts with green shucks had been split for over four weeks but the nuts were still tightly held inside. Freezing temperatures killed all green tissues and turned the shucks black. This rapid color change (from green to black) is caused by the formation of ice crystals that rupture cell walls and destroy cellular integrity. Once the cells are broken, the shuck loses moisture rapidly and dries quickly. What is fascinating to see is how quickly the  shucks pull away from the nuts following a hard freeze.  

    Ripening at the same time as Kanza, I also photograghed USDA clone 75-8-5 (photo above). Unlike Kanza, the green shuck of 75-8-5 pulls away from the nut exposing the nut inside. Once the freeze killed the shucks, 75-8-5 nuts looked ready to fall from the tree.
    The behavior of green shucks following shuck-split affects how fast a pecan dries on the tree. Before the freeze, I harvested a Kanza nut and a 75-8-5 nut and removed one half of their shucks. In the photo below you can see how loosely the 75-8-5 nut is held in the green shuck. In comparison, the Kanza nut is closely held by a much thicker-walled shuck. The Kanza shuck has actually trapped moisture on the outside of the shell preventing the nut from curing  (see photo below).
   If  I wanted to harvest pecans as early as possible, USDA 75-8-5 would be dry and ready to shake long before Kanza, even though both cultivars split shuck on the same date. Kanza really needed the Nov. 1st freeze to open up and allow the pecan to dry.