Tree age and drought stress.

    Looking over our pecan grove,  I've noticed that large, older trees handle drought much better that young trees.  To show you what I'm talking about, I photographed leaves and nuts from two trees. The first was 28-years-old and about 12 inches in diameter, while the second was 9-years-old and about 3 1/2 inches in diameter. Both trees had been grafted to Pawnee and both were bearing nuts.
    In the photo above, the leaf on the left is from the older, larger tree while the leaf on the right was pulled from the young tree. Both leaves were taken from the mid portion of this year's growth. The smaller leaves on the younger tree were also lighter green.

    I  then pulled a cluster of nuts off of each tree. The cluster on the left is from the older tree, while the smaller nuts on the right were pulled from the smaller tree. In a previous post, I mentioned that young trees often produce smaller pecans than mature trees. But this year, the effect will be exaggerated by the drought.
    The smaller leaves and nuts found on young trees is an above ground reflection of the fact that the tree has not yet developed a large enough root system to dominate its surroundings.  A tree with a limited root system has a harder time competing for water and nutrients. Less water and nitrogen means smaller, lighter green leaves and much smaller pecans at harvest.
     Have you ever wondered why young trees respond so well to weed control while older trees seem to tolerate ground cover plants growing right up to the trunk?. It all about becoming the dominate plant in the landscape. From my experience, pecan trees become dominate when the reach 10-12 inches in diameter.

Double-row intercrop system: Pecans and soybeans.

     Back in June, I posted a photo of planting soybeans in our pecan intercrop study area.Today, the beans look good with plants averaging 30 inches tall (photo at right). However, just like area farmers, our soybean crop has struggled with drought all summer long. Fortunately, we had 4 inches of rain during the second week of August, giving the bean crop a needed boost. Plants grew nearly 2 feet taller in the week following the rain.
     Now, another dome of high pressure has settled over SE Kansas and we are back to hot dry conditions. Our bean crop looks good from the road, but on closer inspection you'll find very few pods setting on the plants. Poor pod set is directly related to the hot, dry weather. Needless to say, farming has been a challenge in 2011!

      Despite this year's drought, I still believe that our double-row, intercrop system has great potential for making a new pecan planting financially sustainable during the years of orchard establishment. The grass alleyway between each double row of trees is the unique feature of  this system. The alleyway allows for easy access to the trees for maintenance operations such as grafting, summer pruning and pest control; all without trampling the adjacent agronomic crop..  For those planning a new orchard, here's the planting plan for the double row system (below).

Pecan kernel filling

     Pecans are starting to fill their kernels. Not many people think about the process of kernel filling, but I find it fascinating. The photo at right shows a Pawnee nut that I cut in half this morning. You can plainly see the two kernel halves in cross section, but this photo shows us so much more.
    The blue arrow in the upper right corner of the photo points to a well developed shell. Now that the shell is fully formed, the nut can no longer increase in size.
    The red arrow points to the outer skin or seed coat of the developing kernel. Just inside seed coat (yellow arrow) you can see a light-green gelatinous zone. This is the very start of kernel deposition. Kernel tissue grows from the seed coat inward, eventually filling the seed cavity. Once the cavity is filled, kernel deposition continues, compressing the packing material (green arrow) between the kernel halves and against the inside of the shell.
     If a pecan tree runs out of water during the kernel filling period, kernel deposition will be inhibited. At harvest, drought stricken trees will produce nuts with small kernels that have a hollow crease in the center of each kernel half, both symptoms of inadequate nut filling.  

Pecan nut casebearer--The second summer generation

      For the most part, the 1st summer generation of the pecan nut casebearer is the only generation of this insect that pecan growers worry about controlling. The first summer generation attacks pecans right after pollination, with a single larvae capable of destroying an entire cluster of nuts.
    However, pecan nut casebearer produces 3 generations per year. In the photo at above, you can see a hole or pile of pecan nut casebearer frass at the base of each of these nuts. These nuts were attacked in mid-July by the second summer generation. Since the nuts are much larger in mid-July, it only takes one nut to satisfy the hunger of a casebearer larva. The second and third generations rarely cause economic levels of damage.
    This year we are seeing more nut drop from second generation pecan nut casebearer than in the previous 2 summers. Could this be a foreshadowing of higher casebearer populations next May? We will need to keep a sharp look out and maybe round up some more volunteers for running pherome traps.