Kernel Filling: Kanza vs. Hark

Kanza, 6 Sept. 2018

    This fall I'm taking the time to closely compare the performance of Hark to Kanza. As readers of this blog know, Kanza is my favorite pecan cultivar because it produces high quality kernels, is scab resistant, and produces good pecan crops annually. Hark is a relatively new cultivar that has shown great promise. In comparison to Kanza, Hark has similar nut size, kernel quality, ripening date, and scab resistance. The importance of Hark is that it is protandrous and would be a prefect pollen partner for Kanza, a protogynous cultivar.   However, being a new cultivar, Hark does not have a long track record of performance. How will a 40-year-old Hark tree perform? It will be decades before we find out.

Hark, 6 Sept. 2018

   Today, I stopped by my Kanza and Hark trees to check on their kernel development. Seeing a good crop of pecans on both cultivars gets me excited for the coming harvest season.

    I pulled a cluster of Kanza nuts off a tree then collected a similar cluster from a Hark tree. Holding both clusters in my hand (Kanza on left, Hark on right), I photographed the nuts  to give you a good idea about the size of these nuts. In the photo above, it looks like Hark is a little larger than Kanza.

   I cut a nut from each cultivar to check on nut development (photo above). The shells inside reveal that the nuts are very close in size. But note the thicker shuck on Hark. This is why Hark looks bigger than Kanza while still green and hanging on the tree. I also noted that Kanza is a little behind Hark terms of kernel filling. However, with all the moisture we've received the past few weeks, both cultivars should have no problem packing the inside of the shell with kernel.  

Pecan seedling or grafted tree: How to tell the difference

   Several weeks ago I received and email from a grower that had was having trouble determining if the shoots growing from a newly planted tree were coming from the scion cultivar or from the seedling rootstock. Once you learn what to look for, telling the difference can be easy.
    In the photo at right, the leaf on the left was produced by a trunk sprout originating from below the graft union. The leaf on the right came from the grafted portion of the tree.
    Early in the growing season, juvenile leaves have a reddish appearance compared to the bright green of leaves growing from mature wood (the scion). But by mid summer the color differences are more muted. 
    Look at the color of the rachis of each leaf (the rachis is the stem-like structure to which the leaflets are attached). By mid-summer, the red coloration of the rachis of the juvenile leaf (at left in photo) has faded and is now dull greyish-green. In contrast, the mature (grafted) leaf has a rachis that is bright green in color.

    Taking a closer look at these two leaves reveals stronger differences between juvenile and mature leaves. I flipped the leaves over and took a close-up photo of the rachii of these two leaf types (photo at left). Note that red pigmentation can still be seen on the juvenile leaf, especially at the point where the leaflet attaches to the rachis. The mature leaf has no red coloration.
   Now, look closely at the surface of the juvenile rachis. Note the small hairs that cover the rachis and the petioles of the leaflets. To the touch, these plant parts feel rough especially when compared the the smooth rachis of the mature leave.
     Many pecan growing novices end up caring for a pecan tree for 20 years and never see a pecan crop.  They most likely ended up with a seedling tree because the graft died sometime after planting and then sprouted from the rootstock. To avoid wasting 20 years waiting for a seedling tree to produce, learn to recognize juvenile leaves, then brush up on your grafting skills to topwork any seedlings while they are still small enough to graft. 
    

Pecan kernel filling

    I cut open a Kanza nut today and captured the kernel filling process in progress. The first thing I noticed when slicing the nut in half is that the shell was completely hard. In the photo above, the arrow marked "S" points to the shell. At this point in time, the outer shell of the nut is fully formed and light tan in color.
    The arrow marked "K" points to newly formed pecan kernel. The white creamy color is what we expect pecan kernel to look like. However, inside the white kernel layer is a translucent layer I've marked "J". This is rapidly forming kernel tissue that has yet to fully differentiate into its final solid white state.  The translucent appearance of this not-yet-fully-formed kernel tissue is the origin of the term "gel stage".
    When I first started working with pecans I was given the impression that kernel development progressed from water stage, to gel stage, to firm kernel. It was almost like the water turns to gel then solidifies into kernel. This is not how it works.
   New kernel tissue develops starting from just under the pecan seed coat. As new kernel tissue develops, the water inside the nut is absorbed back into the tree. The amount of "gel" that can be seen inside the nut is dependent on the speed of kernel formation.  The rate of kernel deposition is influenced by weather conditions and cultivar. This is the most "gel" I've ever found inside a Kanza nut. In past years, the gel layer was much thinner.  
   Kernel deposition is not the only pecan tissue I've seen with this translucent appearance. Back during grafting season, I noticed several stock trees with a layer adjacent to the cambium that had a water soaked or gel type look. This was obviously new wood tissue being formed that hadn't fully solidified. 
     Now when I think about pecan kernel development, I think of it in two stages. The first is "ovule expansion". Ovule expansion occurs during the first half of the growing season as pecan fruit grow rapidly in size. The culmination of this stage occurs when the nut achieves its full size and the inside of the nut is filled with water.  The second stage is "kernel deposition". Kernel begins to develop on the inside of the seed coat and works it way towards the center. Kernel deposition continues until the shuck starts separating from the shell (shuck split).

Making a pecan weevil spray

    After a week of showers it was time for me to make an insecticide application for pecan weevil. So, I attached my sprayer, put the tractor in 4-wheel-drive, and slogged my way over saturated ground to apply Warrior II insecticide to protect my nut crop (photo at right). It has been 12 days and nine inches of rain since I last sprayed (mainly for stinkbugs). This time my objective was to kill all weevils in the grove before they can lay eggs inside the nuts.
   I'll need to wait to see how things go during the last part of August and early September before deciding whether or not to make a second weevil spray in a few weeks.