Late January pecan harvest

    Every year we experience several days of unseasonably warm weather during the last week of January. This year was no different. On Wednesday (28 January), the sun was shinning and the temperatures topped out above 70 degrees F (21 C). It was a great day to wrap up the second harvest in many area pecan groves. In the photo above, a local pecan grower employed a swarm of harvesters to cover the ground as quickly as possible.

Pecan nut casebearer's winter home

     Mid-winter is not the usual time to be thinking about pecan nut casebearer, an early-summer, nut-feeding insect pest (photo at right). But if you have been a regular reader of this blog, you will know that we spend a lot of time monitoring this insect during the months of May and June. I have even placed a special tab at the top of this blog so you can follow the progress of moth flight and first significant nut entry each summer. But have you ever wondered where and how the pecan nut casebearer overwinters?

    Yesterday, I was looking at a pecan twig under a dissecting microscope and I found the casebearer's winter home. Nestled at the base of a pecan bud was a small partially grown caterpillar wrapped in a protective case called a hibernaculum. In the photo at left, note how small the hibernaculum is compared to the dormant pecan bud and leaf scar. No wonder it is nearly impossible to spot hibernacula in the field.
    The larva will emerge from its winter home shortly after budbreak and begin feeding on the expanding new pecan shoot. Once the larva grows to full size it will pupate in the stem of the damaged shoot. An adult moth emerges from the pupal case in May and is part of the generation of moths we catch in pheromone traps. This generation of moths eventually lay eggs on nut clusters in early June.

Similar but different: Pawnee, Faith, and Gardner

    We have three pecan cultivars growing at the Pecan Experiment Field that are so similar they are hard to tell apart. Look at the photo at right. Pawnee, Faith and Gardner nuts have the same basic shell appearance with all three nuts sharing a similar apex shape. However, a closer look reveals some differences. On average, Faith nuts are slightly smaller than Pawnee. Gardner is also smaller than Pawnee and the nut is rounder in cross section. Handle a Gardner nut and you'll find the nuts are not a flat as Pawnee or Faith nuts.

    Inside the shells of these three cultivars you will find kernels that also look very similar (photo at left). Pawnee, Faith, and Gardner all yield over 57% kernel and produce quality kernels. Look carefully at all three cultivars and you will see the same light brown mottling on the surface of the kernels. However, this slight kernel discoloration doesn't seem to deter brisk sales for these nuts.
    The rounder shell shape of the Gardner pecan is also reflected in the shape of the kernel. Gardner kernel halves are narrower but thicker than Pawnee and Faith.
     Pawnee is a USDA cultivar created by crossing Mohawk with Starking Hardy Giant. Faith originated from an open pollinated Mohawk seed planted in Arkansas City, KS. Gardner was found as a roadside tree of unknown origin and growing in Gardner, KS. 

Tree architecture varies between pecan cultivars

Osage, narrow and upright

    When growers talk pecan cultivars, the discussion usually revolves around nut size, shell thickness and kernel quality. Nut appearance and taste are important for all those trying to sell pecans but there are other cultivar attributes that are important for those trying to grow pecan trees.
    Often overlooked in discussions of pecan cultivars is a scion's natural tree architecture. Does a tree have an upright or spreading canopy? Do limbs grow out at nice wide angles or are branch angles narrow and prone to breakage? For anyone that has tried to train a young, grafted tree you soon learn that some cultivars are far easier to train into a central leader tree than others.



   

Greenriver, vase-shaped

    Each cultivar has a distinctive growth pattern. Today, I took advantage of a warm sunny day to photograph the architecture of a few cultivars. I chose these cultivars to give you a feel for the variation we see among pecan cultivars.  It is difficult to quantify pecan tree forms but look at enough trees of the same cultivar and some descriptive words come to mind. 
    Osage is a narrow, upright growing tree prone to forming narrow branch angles. Giles is just the opposite. Giles trees grow wide, sprawling canopies that produce drooping branches. Greenriver produces a vase-shaped tree while Chetopa forms a rounded canopy.

Chetopa, rounded canopy

Giles, sprawling canopy

   The trees pictured above are all twenty years old. Does tree architecture change as a tree ages? If the wind, ice, and lightning don't cause major structural damage, the growth form of a cultivar remains fairly consistent. The photos below show a 20-year-old Kanza tree in comparison to a 50-year-old Kanza tree. The older tree is more than twice the size of the younger tree but you can easily see how both trees share the same pattern of tree growth.

Deep freeze propels harvest

   When I woke up yesterday, the thermometer registered 6 degrees F (-14 C) and I knew we would get a full day in of harvest. With the ground frozen hard, we continued our second pass over the pecan grove (photo at right).
    All day yesterday, you could hear the hum of pecan harvesters working in area commercial groves. Because we have had such a wet harvest season this year, many pecan groves were being harvested for the very first time.

   One of the problems with harvesting pecans from frozen ground is that you also end up harvesting chunks of frozen soil along with the nuts. The photo at left shows a close-up of our second harvest nuts as they appear straight out of the harvester. You can see how many chunks of frozen soil were harvested along with nuts and small sticks. If you look closely you can even see ice crystals within the dirt clods.

    The harvested nuts need to be cleaned while still frozen so the clumps of soil can be cleaned out before they thaw and turn into mud. The photo at left was taken two hours after I brought a sample of our harvest inside. The soil clods have thawed and turned into piles of slimy goo that would quickly coat the nuts if run through our cleaning system.

Time to think about tree thinning

   Over the past several years, I have outlined our plan for thinning a block of Kanza trees.  Early on, we recognized that the trees in this block were not all growing at the same rate. Portions of the orchard started to crowd faster than other areas as the trees responded to soil variation within this 3 acre tract of land. We devised a total orchard thinning plan but we have been removing trees only when adjacent trees start to crowd.
    Yesterday, as the sun was shinning and the temperatures reached a balmy 32 degrees F, I walked through the Kanza block to get a feel for which areas would require thinning this winter (photo at right).  Just walking through the orchard its sometimes hard to visualize which sections will require thinning next.

    One method I've used to help plan my next thinning cuts is to plot out the trunk diameters of every tree in the orchard (figure at left). In the figure, each tree in the orchard is portrayed by a green circle that graphically represents trunk diameter as measured after leaf drop in 2014.  All the blank spots on the map are the locations where trees were removed previously.
    Using the map as a guide, I go out to the orchard to visually determine which trees actually need to be removed. I'll stand between two adjacent trees and look up. If the branches are close to touching its time to thin. Let me show you what I mean. 
    On the map at left, I have placed a red box around adjacent trees at two locations in the orchard. At each location, I laid down on the ground between the two trees and took a wide-angle photo straight up. Tree 6-10 is 10.3 inches in diameter while tree 7-10 is 11.0 inches. Just a couple of trees to the south, tree 6-12 has a DBH of  9.2 inches and tree 7-12 is 8.3 inches in diameter. From the map it looks like trees 6-10 and 7-10 are almost touching while trees 6-12 and 7-12  still have some room to grow. Now lets look at the photos.

    The photo at right shows how close the canopies of trees 6-10 and 7-10 are to each other.  The dormant stems of each tree are not touching each other yet but add another summer of stem growth and a full load of leaves and you would see a closed canopy during the summer of 2015. I'll be thinning some trees out of this area of the orchard.

    Moving down the row to trees 6-12 and 7-12, the photo reveals that there is still plenty of space between these two trees (photo at right). In this case, I won't need to thin trees in this portion of the orchard for a year or two.
    We have been thinning this orchard a little bit at a time since 2012. In that time, I've come to realize that our Kanza trees start to crowd when trunk diameters of adjacent trees both exceed 10 inches. However, you must remember thinning decisions should be based soley on your particular soil type, initial tree spacing, and cultivar. We started this Kanza block at a close tree spacing of 30 feet x 30 feet. The closer the initial tree spacing, the smaller the  diameter the trees will be when thinning becomes necessary.