Thursday, June 25, 2020

Directive pruning leads to increased lateral branching

    Earlier this spring, I showed you how I use Directive Pruning to reshape a top heavy tree and promote the growth of a single, central leader. The photo at right was taken one month after my initial pruning efforts. In the photo, you can see that the central leader has taken off and that new lateral branches are forming lower down on the main trunk.
    It is important to allow these lower branches to grow for two reasons. First, they increase the leaf area of the tree allowing it to capture more of the sun's energy via photosynthesis. And secondly, lower branches stimulate diameter growth of the trunk resulting in a stronger tree.
    In the photo at left, you will note that these new lateral branches have formed nice wide branch angles. This branching characteristic is the result of last year's tree training. During the previous growing season, I carefully removed all stalked primary buds from the central leader as it grew taller. A year later and stimulated by directive pruning the top of the tree, secondary buds have started growing along the lower portion of the trunk. As a general rule, branches that originate from secondary buds create strong branch angles.
   Over the years, I have found that I can direct the growth of pecan trees with a few simple pruning cuts on actively growing shoots. If I pay attention to tree growth during the growing season, I can largely eliminate the need  for making large, corrective-pruning cuts during the dormant season.

Sunday, June 14, 2020

Heavy Kanza Nut Set

    Last week while I was scouting nut clusters for pecan nut casebearer activity, I was surprised to find that my Kanza trees had set an unusually heavy crop. It was just not the fact that a high percentage of terminals were bearing nut clusters but each cluster contained an usually large number of nuts (photo at right shows a cluster of nine Kanza nuts).
    From past experience, I've found that Kanza usually produces 3 to 5 nuts per cluster. So why the the difference this year? The number of pistillate flowers produced by a pecan tree is the product of the previous season's crop load, the nutritional health of the tree, and rainfall during the kernel filling period the prior summer.
    Last year we had ample rainfall throughout the growing season and I always try to make sure my trees receive adequate fertilizer both spring and fall.  In addition, last year I used summer shaking to  reduce a heavy crop load.  The result of this combination of weather and crop management turned out to be ideal for promoting flowering this past Spring. 
    There is no way a pecan tree can grow and fill a canopy full of 9-nut clusters. This kind of crop load will lead to limb breakage and poor kernel filling. To reduce the crop load, I plan to shake all my Kanza trees once again this summer.

Saturday, June 13, 2020

Pecan Nut Casebearer arrives late

    I've been scouting my orchard every other day for the past 10 days watching for the first signs of pecan nut casebearer activity. After inspecting over 100 nut clusters, I found a single casebearer egg and even one nut damaged by a casebearer larva.
    Pecan nut casebearer eggs are difficult to spot in the field because of their small size. However, when I do find them, they are always placed near the tip of the nut just below one of the four sepals. In the photo at right, the red arrow points to a single white casebearer egg. When the egg hatches, the emerging larva will crawl to the base of the nut and start chewing its way into the nut's interior. 
   The damage caused by casebearer feeding is very distinctive. In the photo at left, the yellow arrow points to a pile of insect frass at the base of a nut. As the larva tunnels into the nut it pushes all its excrement out the entrance hole creating a pile of brown waste between the nut and the peduncle. In addition, the larva ties the nut onto the stem with numerous fine silken threads. This prevents the nut from falling off the tree before the larva can move to other nuts in the cluster. A single casebearer larva will destroy 3 to 4 nuts while completing its life cycle.

  I'll be making a pesticide application aimed at controlling casebearer on Monday June 15. That's 5 days later than my average spray date of June 10th.

Tuesday, June 2, 2020

Forcing pecan grafts

    In the world of horticulture, the phrase "forcing graft" means to prune a newly grafted tree in such a way as to direct all the tree's energy towards to growth of the scion. During early June, I try to visit each newly grafted tree to check of graft success and to "force the graft". The tree pictured above is typical.
    The scion has successfully grown and is making new shoots. However, sprouts originating from below the graft union are threatening to out compete my graft. Shoots growing from the seedling rootstock have the red pigmentation typical of juvenile pecan tissue. The scion, on the other hand, was cut from mature pecan tissue and buds out fully green in color. To direct all the growth towards the scion, I pruned off all the stock sprouts (photo above). This simple procedure is key for promoting rapid scion growth. In fact, pruning off stock sprouts is something that needs to be accomplished every 3-4 weeks during the summer or until the scion becomes totally dominate over the rootstock.