Tuesday, December 11, 2018

Twigs falling from pecan trees

    This afternoon I decided to trim up some seedling pecan trees growing along the south edge of my farm. These trees are growing in the worst soil on my farm, an eroded Dennis silt loam that is shallow and very prone to drought. However, I can't bear to cut down  these squirrel-planted pecan trees even if I'll never harvest a nut. I can still enjoy the shade.
    When I drove up to the trees I noticed the ground was littered with small branches that look like they had been cut from the tree with the leaves still attached. I picked up four of the fallen shoots and brought them back to the house to photograph (photo at right).
    If you look closely at the cut end of the branch you will note that the outer portion of the stem was cut smoothly but the center portion actually broke off in a gust of wind (photo at left). This type of limb pruning is caused by a long-horned beetle called a "twig girdler". You can see a photo of this beetle in a previous post.
     As I carefully inspected each of the four limbs I collected , I found one with a partially completed girdle (photo at right). I bet the insect got frustrated by constantly backing into that small branch just below and decided to try a different location. However, this partially completed girdle gives us a good idea how deep twig girdlers chew into pecan branches.

   Looking even closer at the twigs, I noticed a oviposition site at the base of old leaf scar (photo at left) . Twig girdlers carve a crescent shaped hole in the twig and deposit their eggs inside. Looking at the entire stem I found several oviposition sites, always placed just below a leaf scar.
    Twig girdlers adults are active in late summer (August-Sept.). They girdle pecan stems at this time of year so that all the carbohydrates created by the leaves can not be translocated down to the roots and end up accumulating in the stem above the girdle. Eggs laid in crescent-shaped scars hatch the following spring, with the resulting larvae feeding on the nutrient rich twigs.
    In commercial orchards, twig girdler is rarely a problem because sprays aimed at controlling pecan weevil during the month of August also control twig girdler. For non-sprayed pecan trees, twig girdler populations can reduced by picking up all fallen twigs during the winter months and burning them (thus killing the next generation of girdlers).  

Tuesday, November 27, 2018

Pawnee needs crop load management

    Pawnee is one of the most popular cultivars grown in our area (photo at right). The popularity of Pawnee is based on two factors; the nuts are big and they ripen early. However, Pawnee is a high maintenance cultivar. Pawnee is susceptible to pecan scab and the crop needs to be regulated to insure well filled nuts at harvest.
     Today, I collected a few Pawnee nuts from trees at the old Pecan Field Station. In previous years, I reduced the crop load of overloaded Pawnee trees by using a trunk shaker. Now that I've retired from the University, the field station has been abandoned and Pawnee was allowed to over-produce in 2018.

    I collected Pawnee nuts from two areas. The first was a mature orchard with nuts hanging from every terminal. Prior to 2018, these mature Pawnee trees received a good summer shake every year they loaded up with nuts. The second spot was in a young orchard, just starting to produce nuts. Like all young pecan trees, these Pawnee trees had not reached the age when over-cropping becomes a problem.  The young tree produced normal-sized Pawnee nuts while the over-loaded trees produced much smaller nuts (photo above). When I held those smaller nuts in my hands I could already tell the kernels inside were going to be shriveled.

    As I suspected, the kernels produced by the over-loaded Pawnee trees were smaller, poorly filled, and even darker in color. The two kernels on the far right in the photo above were so paper thin that they would be inedible.
   Pawnee is a cultivar that requires a high level of care but when treated right can produce beautiful pecans. Growing Pawnee profitably means adopting a good scab control program and shaking off nuts during the years when the trees set an over-abundant crop.     

Thursday, November 22, 2018

Thanksgiving harvest

Harvesting native pecans near Chetopa, KS

  Thanksgiving is an American Holiday with a long tradition of family gatherings and roast turkey dinners. But here in pecan country, today's bright sunshine and dry soil conditions makes it the perfect day to pick pecans. By mid-morning, I could hear the familiar drone of pecan harvesters working in the native groves near my farm. I took a quick drive around the area and found that every grower was celebrating the Thanksgiving holiday the same way,  by picking pecans. I can't think of a better way celebrate the fall harvest season. 

Sunday, November 18, 2018

Evaluating nut samples

    Last week we had a light snow fall that covered the pecan grove with about two inches of wet snow (photo at right). The snow turned out to be only .16 inches of precipitation but the cold weather that followed meant that the orchard floor stayed snow covered and wet for several days. Wet soil conditions means that I was unable to finish harvesting my pecans. So, I parked the tractors and moved inside to start cracking nut samples I had collected from the pecan breeding block.
   At shuck split, I collected at least 25 nuts from each tree. I let these nuts air dry for several weeks then began the process of measuring, weighing, and cracking nuts.
    The first step in my evaluation process is to record the diameter size class of each nut in the sample. I do this because every nut ever brought to a shelling plant is run through a nut sizer in preparation for cracking. Pecans are sized by a series of steel cages with various size slots for nut to fall through. The sizes are recorded in sixteenth of an inch increments. A size 12 pecan falls through an opening 12/16 or 3/4 of an inch wide. I use a series of end wrenches (measured in 1/16 increments) to simulate the nut sizing process (photo above). In the photo, note a nut stuck in the 15/16 wrench. This same nut passed easily between the jaws of the 16/16 wrench (1 inch) and would be classed as a number 16 diameter pecan. By measuring every nut in a sample I can develop a size profile for each clone. The sample I was processing when I snapped these pictures was 50% size 15 and 50% size 16 nuts.

    The next step in my nut evaluation process is to weigh 10 randomly selected pecans. This weight will give me an average nut weight but can also be used to calculate average nuts/pound. I use a gram scale to weight the nuts (photo at right).  This sample weighed 101.97 grams. This nut averages 10.197g per nut and if you divide the conversion factor of 453.6 by the average nut weight in grams you'll find that this particular pecan averages 44.48 nuts/lb.
    With the inshell nuts weighed, I next use a hand cracker and shelling tool to extract the kernels from the shell. In cracking the nuts, I use a light touch because I take great care in trying to extract full kernel halves from every nut.
    Once all the kernels are removed from the ten nut sample, I weight the kernels. This sample had kernels that weighed 54.91 grams. By dividing the kernel weight by the nut weight and multiplying by 100, I can calculate the percent kernel for this nut sample. In this case the math works out like this:  (54.91/101.97)*100=53.85% kernel.
    In addition to the hard numbers that I record on nut size, weight and percent kernel, I take notes on kernel color, ease of extracting full halves, adherence of shell packing material, and any glaring kernel defects.
    As I collect this information year after year, I should be able to recognize those trees that produce quality pecans every year. Hopefully, that will lead to some new cultivars.