Thursday, March 27, 2014

A little dormant pruning

   I've got a lot of young trees on my farm and not every one of them has grown according to the strong central-leader plan. Take this tree for example (photo at right). This Kanza tree looks vase-shaped with several side shoots competing with the central leader for sunlight. I guess I should have made a few more trips to the pecan orchard last summer to direct the tree's growth with summer pruning.
    At this time of year, I'll make just a few corrective pruning cuts help shape this tree. I don't like to cut off too much at this time of year because dormant pruning often forces the tree to regrow in unexpected ways.
   As I approached the tree, I got a good look at this young tree's branch structure (photo at left).  Notice that most limbs have formed nice wide-angled attachments. However, look at the lowest limb on the tree pointed out in the photo by the orange arrow. This limb is almost the same diameter as the central leader and is growing upward in such a way as to directly complete with the main trunk for supremacy. This limb is a great example of how forked trees can develop over time if a pecan tree is left to grow unattended.
    Its easiest to spot tree structural problems during the dormant season when limbs are not hidden among the leaves.  So once I spotted this low limb growing straight upwards, I got out my pruning saw.

     Before I cut off the limb, I took out my sharpie pen and drew a line indicating the proper position for removing this limb (photo at right). By making an angled cut as shown, I'll leave the smallest possible wound on the tree and a wound that will heal over quickly. Since the tree was still dormant, I was able to cut some nice Kanza scionwood from the pruned-off branch.

   Next, I turned my attention to some upright growing limbs a little higher up into the tree's canopy (photo at left). The arrows in the photo point to two strongly upright growing limbs that had developed on the side of the tree opposite from the limb I had already removed (see above). In this case, I am not going to remove these limbs entirely. I am, however, going to head these limbs back to outward growing side shoots.

    I simply cut off the upright growing portion of these two shoots and left all outward growing shoots in place. Look carefully at the photo at left and you can see two fresh pruning cuts.
    After these cuts were made the upper portion of the central leader became fully exposed to sunlight. The additional sunlight should stimulate the development of lateral branches further up the trunk and encourage the leader to continue growing straight up.
   I'll be back to this tree once spring's new growth has begun and I can make additional pruning cuts to direct the growth.

Wednesday, March 26, 2014

Early spring pruning on last year's bark graft

    I made a quick trip into my pecan orchard this morning to look at last summer's grafts. I stopped by the tree pictured at right to check the health of the scion and to trim the graft union. I grafted a Kanza scion onto this 1.5 inch diameter tree last May. After pruning the scion to one shoot in early July, this graft put on five feet of new growth during the summer of 2013. I removed the deer cage and quickly checked the scion's bark for signs of winter injury.  Even though this new graft had grown vigorously well into the Fall and this type of late growth can be prone to winter injury, my Kanza stem had green and healthy looking tissues inside the bark.
    I next turned my attention to the graft union. Last summer, I had cut off the green plastic tape that held the plastic bag around the scion allowing it to grow in diameter without being restricted. I left the remaining grafting wraps in place (photo at left). As is often the case, it looks like a bird had ripped open the plastic at the top of the stock, split the aluminum foil apart, and feasted on the ants that take up residence under the foil wrapper. I guess I should have taken my own advice and painted the graft union with white paint last summer.
    Once I removed all the graft wrappings, I could see how the tree was attempting to grow over the large wound I made by cutting the stock and inserting the scion (photo at right). The scion had grown to roughly 1/3 the diameter of the stock. Callus tissue had formed around the scion and had begun to cover the cut surface of the stock. Between the bark and the wood of the stock, I could see that a roll of callus tissue had developed part way around the circumference of the tree. This roll of callus is thickest near the scion then seems to dive down under the bark farther away from the scion.

    On the opposite side of the tree from the scion, the bark of the stock dies downward. To encourage rapid wound healing, I like to trim out the dead corner of the stock. I make the cut at about a 30 degree angle which seems to follow the natural way the tree is already forming callus tissue (photo at left).

      After trimming the stock,  I'm ready to replace the deer cage and move to the next tree (photo at right). Note that I still have the graft tied to a bamboo stake to prevent wind damage. The bamboo is attached to the stock with electrical tape and I used flagging tape to attach the scion to the stake. I'll keep the stake in place until the graft union is completely healed over. Once growth starts in the spring, I'll come back to this tree to make some "directive" pruning cuts to ensure I maintain a strong central leader.

Thursday, March 20, 2014

Evaluating nut samples from the breeding project

    Growers that attended the Kansas Nut Growers Association meeting last weekend had the opportunity to look at all the nut samples we collected from our pecan breeding plot (photo at right). We asked each each grower to pick out their top 5 and jot the tree number down on a file card.
   Out of 216 total samples, 46 different nuts were rated as "top five".  Some of the more popular selections are shown in the photographs below. It is interesting to note that some growers seem to be most interested in large nut size while others look for the brightest, plumpest nut meats. You can count me as a member of the bright, plumb kernel team--I like the looks of KT149 and KT329. However, we will need to look at all of our trees for several more years before we can make an educated guess as to which seedlings might make outstanding new cultivars worthy of advanced testing.

Monday, March 17, 2014

Cold injury on Pawnee: Temperature and fruiting stress

   Pawnee is a large, early-ripening pecan cultivar grown by many northern pecan producers (photo at right). In previous years we have noted cold injury on Pawnee when winter temperatures drop below -10 F. So I thought it would be interesting to see how Pawnee fared following a colder than normal winter in the Mid-West. Recently, I asked some friends to provide me with some Pawnee shoots cut from their orchards growing near Columbia, MO. The lowest temperature they recorded at their location was -12 F. For comparison, I cut some shoots from our trees growing near Chetopa, KS where we recorded a winter low of -3 F.  
    In looking for cold injury, I selected both shoots that produced pecans last fall (i.e. fruiting shoots) and shoots that produced only leaves in 2013 (i.e. vegetative shoots). Using my knife, I peeled back an area of bark on each shoot to check for internal browning in the bark and cambium (indications of cold injury).

   The photo at left shows a vegetative shoot I cut from a Pawnee tree growing at the Pecan Field (KS). Inside the oval is a close-up of the tissues inside this twig. Note that everything inside the bark looks green and healthy. No cold damage here. A temperature of -3 F was not cold enough to cause injury to this Pawnee stem.

    Now let's look at a fruiting shoot cut from the same tree (photo at right). Again, a close-up of internal bark tissues is shown inside the oval. Note the internal browning of both the bark and the cambium. In this case, the stress of producing pecans caused this shoot to suffer cold injury at -3 F.

    In Columbia MO the winter low was -12 F. In the photo at right, I've placed two Pawnee shoots collected from an orchard just outside of Columbia. A vegetative shoot is on the left and a fruiting shoot on the right. A close-up of the internal bark for these two shoots is shown within the oval (in same left to right order).
    At -12 F both Pawnee shoots showed signs of internal browning. The vegetative shoot had only very slight discoloration while the browning observed within the fruiting shoot was intense.
    From this year's observations and observations we've made following previous winters, it also looks like Pawnee usually develops cold injury problems when temperatures drop below -10 F. In addition, it is clear that the stress of nut production can reduce the cold hardiness of Pawnee shoots helping to intensify alternate bearing .

Tuesday, March 11, 2014

Early spring tree thinning

     With warm sunshine overhead, today was a good day to cut some pecan trees down (photo at right). We removed six more trees from our Kanza block according to our pre-determined tree thinning plan.
  The trees in this block are growing at an incredible rate. Just look at the cross section of one of the trees we cut down today. Over the past 4 growing seasons, the annual growth rings of this tree averaged more than 1/2 inch per year (photo at left).  However, not all trees in this block are growing at the same rate. Generally speaking, the trees on north end of this planting are growing faster than the trees farther south.  This variation in tree growth rate is largely due to a gradual change in soil conditions.
   Every winter I walk through the planting to measure trunk diameter and look up at tree canopies to see if they are starting to get too close. Looking up is the best way I know of determining when to thin out trees.
    Here's a series of maps that tells the story of our the thinning efforts over the past three years. In looking at these maps, each green circle represents a tree and the relative diameter of each tree is depicted by the size of the circle. The red lines cut through all the trees that will be removed once the entire field is thinned. I placed a black circle over the trees that are to be removed during each particular thinning year. As you look at the maps, you'll note that the trees slated for removal one year disappear off the map of the next year's tree removal plan.
     Thinning an orchard over several years has many advantages over thinning the entire block at one time.
     1. Trees are removed in time to prevent sections of the block from becoming overcrowded.
     2. The number of trees removed per year is minimized allowing yield for the entire block to remain at a high level.
     3. The work of thinning a block of trees is spread out over several years.
        When established in 1995,  there were 144 seedling trees planted in this block. These trees were then grafted to Kanza during 1998-2000. Starting at tree age 17, we began our planned tree thinning operation. We removed 7 trees in 2012, 5 in 2013, and 6 in 2014. At this point, we have removed only one-quarter of the trees that will eventually be cut to complete the thinning plan. I'm sure more trees will need thinning a year from now.   

Monday, March 10, 2014

Judging kernels

   Over the past couple of weeks, I've been looking at a lot of pecan samples. We collected nuts from 216 trees in our pecan breeding plot and cracked 10 nuts from each tree. We evaluated those nuts for size, percent kernel, and kernel appearance. Nut weight and percent kernel are easy measurements to determine with the aid of a gram scale and calculator. However, when it comes down to kernel appearance things get a little more difficult to quantify.
   A smooth, golden kernel color is most desirable for pecan. Light-colored kernels are described by the official USDA pecan grading system as "Fancy". However, in evaluating hundreds of nut samples, my eye detects subtle color differences even among kernels that would be graded as Fancy. The photo at right demonstrates these subtle color differences. At the top are the lightest colored kernels I found among our breeding plot nuts. In the middle are kernels with a beautiful golden pecan color. The kernels at the bottom are ever so slightly darker than the ones above but still have a pleasing sandy coloration. Which looks best to you?

    Not all the nut samples we cracked had beautiful even-colored kernels. It is so disappointing to crack open a large, thin-shelled nut only to find an ugly pecan kernel inside. I found two types of kernel defects (photo at left). The first was the appearance of dark veins that cross the surface of the nut. The second was a mottling of the kernel surface with dark patches. I even found a tree that produced nuts with both veins and mottling. These kernel discolorations do not effect kernel taste but the lack of "eye-appeal" would make selling these types of kernels very difficult. 
    All nut samples from our breeding project will be on display during the KNGA annual meeting. Click on the event tab above for details.

Thursday, March 6, 2014

Wheel bug egg mass

    The sun shine felt good today after last weekend's winter cold snap. In fact, all the snow has melted and we could get back to collecting pecan scionwood. While we were cutting scions we discovered a large egg mass (photo at right) on a pecan branch. The eggs are lined up in neat rows, are black in color, and topped with a white cap. Later this spring, these eggs will hatch and dozens of wheel bugs will emerge to start searching of other insects to feed on.

     The wheel bug is one of the most common insect predators found in pecan tree canopies. These insects will grow quite large and are easily recognized by the red antennae and  prominent cogged "wheel" on their backs (photo at left).  So if you are out pruning pecan trees make sure to leave the egg masses of these beneficial insects in place.  

Monday, March 3, 2014

Let your trees tell you when to fertilize

    Winter returned over the weekend covering area pecan groves with a blanket of new snow (photo above). The temperature dropped down to 2 F this morning in the Neosho River flood plain outside of Chetopa, KS. At this time of year, pecan growers are supposed to be thinking about making their Spring fertilizer application, not shoveling snow and hauling firewood.
     In timing the spring fertilizer application, it is important to remember that soil nutrients are most readily adsorbed by actively growing pecan roots. With all the cold weather we've had this winter, pecan roots are still laying dormant it the cold ground. New root growth will not start until soil temperature begin to rise with the coming of spring.  

    Because roots are buried in the soil, it is not easy to see when their growth begins in the Spring. However, watching for the earliest sign of bud swell is a good indicator that a pecan tree is coming out of dormancy and spring root growth has begun. I carefully watch lateral buds on one-year-old shoots. The first sign of bud swell will be the splitting of the outer bud scale (photo at left). When this happens, I know that root growth has started and it is a good time to spread fertilizer under my trees.