Friday, May 19, 2017

Checking on pecan pollination

    Yesterday, I wandered through our pecan cultivar trials to check on the progress of pecan pollination.  At this point, we are half way through pollination. All of the protogynous cultivars are releasing pollen and the protandrous cultivars have receptive pistillate flowers. Pawnee is a protandrous cultivar that is now displaying large, red stigmas on the ends of pistillate flowers (photo above).  The catkins on Pawnee shed their pollen a while back and have now dropped to the ground.

     The pistillate flowers of Kanza are fully pollinated (photo at left). Stigmas of female flowers dry up and turn black once they become pollinated.
    Kanza, being a protogynous cultivar, has late pollen release. Yesterday, Kanza catkins were releasing millions of pollen grains into the warm springtime winds.

    One thing I noticed about pecan flowers is that pistillate flowers of protogynous cultivars are smaller than pistillate flowers of protandrous cultivars.  In the photo above, you can see this size difference. Posey is protogynous while Pawnee is protandrous. By the end of the growing season the nuts of these two cultivars will be roughly the same size.

    While inspecting pecan flowers, I was also reminded that the color of receptive stigmas can vary from green, to orange, to bright red. The photo above illustrates some of this color variation. Both Major and Waccamaw had fully receptive pistillate flowers yesterday. Major displayed green stigmas while the Waccamaw stigmas are bright red. Since pecan trees are wind pollinated, stigma color has zero impact on pollination success. However, stigma color can sometimes be used to help identify certain cultivars. 

Wednesday, May 17, 2017

Finishing up the grafting season

   Last weekend, I finally finished grafting pecan trees in my orchard. After the flood receded, it seemed like I spent a week in rubber boots wading in the mud to finish up making bark, arrowhead, and 3-flap grafts. I've been grafting pecan tree since late April this year and those first grafts I made are starting to break bud (photo at right). Now it was time to finish up.
   Not every tree is cooperative with the grafting process and the last tree that I needed to graft this year turned out to be a graft failure from 2016 (photo at left).  Its a good thing that I had strong trunk sprouts grow up last summer to provide a perfect spot for grafting this Spring. My first step was to remove the failed graft and trim the tree down to a single trunk.
    I choose to keep the larger of the two sprouts for my new central leader. I trimmed off the old failed graft and the smaller trunk sprout with one cut using a chainsaw. I made the cut at about a 45 degree angle to aid in rapid wound healing.
    I cut the remaining portion of the tree at about 2 feet above ground level. At this point, the tree was about one inch in diameter--somewhat small for a bark graft. I selected a small diameter scion from my cooler and held it up to the stock. This is how I search for a flat spot on the stock wide enough to suit my scion (photo above right).

   In choosing a flat spot to insert the scion, I also took into account the locations of buds on the stock. Each bud has a bud trace or small branch of wood that grows up into the bud. If you try to insert a scion right under a bud on the stock, the scion might get hung up on the bud trace. I found two buds on the stock tree that I needed to avoid. In the photo above, the red arrow points to a bud at the very top of the stock. This location looks like a nice flat spot, but the bud trace could create a problem for inserting the scion.  I found a second bud in the grafting zone (yellow arrow) and I chose to avoid this bud also. Ultimately, I decided to place the graft in location of clear bark that seemed just wide enough for the scion (the scion in the photo hovers above that location).
    The way I carve my scion for a bark graft means that I always place the scion on the left side of the split in the stock's bark. Keeping that in mind, I made the downward slice in the stock's bark on the very right side of the area I had identified for scion placement. I proceeded to carve the scion and staple it in place (photo at left).

    This year's grafting season for me ended up the same way as always--covering a graft with aluminum foil and plastic bag, then attaching a bird perch. For me the end of the grafting season means the beginning of the directive pruning season, especially on trees grafted in 2016.

Monday, May 15, 2017

Cages protect young pecan trees from deer browse

    A picture may be worth a thousand words but the two photos above teach a valuable lesson. The photo on the left shows an unprotected seedling pecan trees that has been heavily browsed by deer. The tree on the right is enclosed by a cage constructed of welded wire fencing. This tree has a full canopy of leaves and has already made over ten inches of new shoot growth.

    Although browsing doesn't kill the tree, the removal of new growth ultimately stunts the growth of the tree.  The photo at right shows the terminal of the tree that was browsed. The yellow arrow points to the stub of this year's new growth left behind after a deer bit off the top of the tree. You can tell it this stump  is from the spring flush of new growth because of its green color.  Once the deer removed the first flush of new growth, its taken the secondary buds a couple of weeks to start breaking.
    The lesson I've learned is that tree cages are now necessary for every young tree on my farm.  I use 2 x 4 inch welded wire to build the cage. I've used both 4 foot and 5 foot tall wire but find that 4 tall works just as well in curtailing deer browse. I've used both light gauge and heavy gauge wire but find that the greater expense of the heavy gauge wire is offset by the cage's greater durability. As the trees grow above browse height, I'll remove the welded wire cage then re-use the cage to protect newly planted trees.

Thursday, May 11, 2017

Training last year's bark graft

    When grafting a vigorously growing tree with a bark graft I often produce a tree with 5 to 7 feet of new growth on the scion during the first summer. I achieve that kind of growth by meticulously  pruning to preserve a strong central leader. But by the end of the growing season, I usually find that I've created nothing but a tall, branchless tree. When the one-year-old graft breaks bud the next spring it seems like all the new growth is confined to the very top of the tree (photo above, right). How am I going to promote lateral branch formation with a tree like this?  All it takes is some careful directive pruning.

   In pruning this tree I start at the very top then work my way down.The photo at left shows the cluster of new shoots that have developed at the very top of the tree. If I were to leave all these shoots in place, I would quicky lose my central leader and the tree would be topped by a sprawling assembly of branches pointing in every direction but straight up. In addition, allowing the tree to grow freely at the very top of the tree will create a top-heavy tree that causes the tree to bend over under the weight of the foliage.

     My first pruning cuts were made to encourage the growth of a single new leader. Here's where I use the 2-foot rule in tree training. In the photo at right, you can see that I removed all the the new shoots in the area of the trunk two feet down from the apex of the shoot that I have choosen to become the new central leader.

   When pruning off all the lateral shoots that are directly competing with the new central leader, I was careful to leave all secondary buds in place (photo at left). A few of the secondary buds had started to push and that's OK. The just-emerging shoots from secondary buds won't be able to catch up with the strongly growing central leader. In addition, shoots that develop from secondary buds form lateral branches with wide crotch angles (a good thing). 

    After pruning the top of the tree using the two-foot rule, the top of my tree has a single central leader and has lost its bushing appearance (photo at right). My next pruning task was to work my way down the stem and thin out the dense array of lateral branches that I found growing there (photo at right). There is no way the tree could support that many lateral branches all within about 18 inches of trunk.

    I removed more than one-half of the lateral branches that had formed on this portion of the trunk. In pruning lateral branches, I was careful space out the remaining branches both up and down  and around the trunk (photo at left).  After pruning, the entire tree no longer appeared so top heavy with foliage
    Thinning out lateral branches near the top of the tree has an additional advantage. Buds lower down on the trunk will be stimulated to grow and form branches along the entire length of the last year's scion growth.

    Stepping back from the tree that I just pruned, I could see that the new shoots and foliage were now better distributed along the main trunk (photo at right). The ladder in the photo is 4 feet tall to give you a better idea of the size of the tree I was pruning. With lots of lateral shoots developing already this year, my single shoot graft should turn in a well bushed out tree by the end of its second growing season. Maybe by year three, I'll be producing a few nuts on this tree.