Wednesday, January 29, 2014

Cutting quality scionwood

    Even though it's freezing cold outside today, it won't be too long before we will need to go out into the orchard and collect some pecan scionwood. The other day I cut down a young pecan tree (a really poor cultivar!) and it gave me the opportunity to cut off some pecan branches so I can show you how to find and select quality scions.

   Let's start by looking closely at a pecan branch. The best scions come from last year's new growth. In the photo above, you can see 2-year-old wood on the left and one-year-old wood on the right. Two-year-old wood is generally more grey in color and all the primary buds are missing. The reason 2-year wood has missing primary buds is because last spring, these buds opened and produced  catkins.  Two-year wood ends in what is called the annual growth ring which is actually a ring of closely spaced bud scars. One-year wood has a more brown or reddish-brown color with primary buds still firmly attached to the stem. Note that the first few buds on the 1-year wood are small and you don't see a prominent primary bud until about two inches up the stem. When I cut scionwood from a tree, I take only 1-year wood and make the first cut just above the annual growth ring.

     The best scions are collected from one-year-old shoots that are at least 2 feet in over-all length. After I cut the shoot off the tree, I cut the wood up into individual scion sticks that are each 6 to 7 inches long and contain at least 3 buds (photo at left). I try to make sure that the upper most bud on each stick is at least one inch below the top of the scion. I always discard the terminal piece of wood (stick at far left) because it is too small in diameter for the grafting techniques I use.

   Once a graft is made, the vigor of emerging buds from a scion is largely dependent on the amount of energy stored in the wood of the scion stick. In the photo at right, I've cut into each stick pictured above to reveal the amount of wood inside. The scion cut from the base of the one-year wood has the thickest layer of wood and the greatest reservoir of stored energy. As you go up the stem, you'll note that pith seems to become more prominent and the actual woody tissue more narrow.  The base of last-year's growth is the oldest portion of the stem and has had an entire growing season to lay down wood. As a stem grows in diameter the wood also compresses the pith into a narrower band of corky tissue.
    When I'm grafting, I can always tell if a scion is going to make a successful graft based solely on the ratio of wood to pith. The scion with a lot of wood and tiny pith will always out-perform a scion that's mostly pith. In cutting scionwood I always discard the terminal piece for two reasons; the buds are too close together and the stick is too pithy. In looking at the scions above, I'd choose to graft with the two sticks on the right. The second stick from the left is marginal and I'd use it only if I've run out of other scion choices.
   Remember, when you are cutting scions, you don't need to slice into each piece to check the wood to pith ratio. Simply look at the cut surface at the top of each scion and note the diameter of the pith as compared to the overall diameter of the stem. The pith diameter should be no larger than 1/3 the diameter of the entire stick.

Thursday, January 23, 2014

Notes on Jayhawk pecan

    Jayhawk originated as a seedling of Giles planted by Lewis Harris on his farm near Wichita, Kansas.  This seedling cultivar first came to light when entered into the Annual Nut Evaluation of the Kansas Nut Growers Association back in 1989.
    Jayhawk has been under test at the Pecan Experiment Field for several years and we have a pretty good feel for how this cultivar performs. On the plus side, Jayhawk is precocious, productive, scab resistent and produces a medium-sized, thin-shelled nut. This cultivar has a protogynous flowering habit and ripens nuts 10 days after Pawnee and 6 days before its parent, Giles. Jayhawk trees have good tree structure and are easy to train.
    Back in 2011, I noted a single negative trait that seemed bad enough to keep Jayhawk off my top ten list. Jayhawk kernels appeared mottled with darker brown patches giving the nut meats an unappealing appearance. At that time, I blamed the blotchiness on the 2011 drought. So this year, I was curious to see what Jayhawk kernels would look like  following a cool summer with ample rainfall (photo at right). In comparison to 2011, the 2013 Jayhawk kernels had much better color but were still far from perfect. The upper side of the kernel halves had only a few minor brown patches but the underside displayed a mottling pattern that makes the kernel look "dirty". Although the patches of kernel discoloration seem to have zero effect on kernel flavor, it will be hard to convince consumers to place "dirty" looking pecans in their mouth.
   Jayhawk is a great example of a pecan cultivar that looks almost perfect but probably shouldn't be propagated.  A single serious defect (blotchy kernels) is enough for me to discard Jayhawk as a potential recommended cultivar. 

Wednesday, January 22, 2014

Pecan oddities from the cleaning table

   This week we've been looking at thousands upon thousands of pecans streaming across the inspection table as we clean the 2013 pecan crop. As we look to remove  rocks, stick-tights and damaged nuts, we will come across a few genetic mishaps.
   What might look like one big pecan split in two is actually two fully formed nuts joined at the base (photo above). These twin pecans had their genesis all the way back during pistillate flower formation when a genetic miscue led to the creation of a double flower. A double flower has two stigmas, two ovaries but a fused shuck. At harvest, a twin nut falls free from its shared husk revealing  a pair of nuts with shells fused only at the very base. Crack open the nuts in the twin and you will find two kernel halves in each pecan just like a normal pecan.

   Harder to spot on the cleaning table are nuts that don't have the normal two kernel halves inside. The other day we spotted a nut with three cotyledons inside (photo at left). Viewed on its side the nut looks quite normal. However, look at the nut's apex and you can see that the shell has three distinct faces signalling the fact the kernel inside is divided into 3 pieces instead of the normal two. Over the years, we have also come across pecans with a single cotyledon and even nuts with four kernel pieces. 

Misshaped pecans
     This year, we also found a couple examples of pecans that look like their growth was simply pinched off. We found a nut with an extremely narrow, pointed apex as well as a nut with a pinched of base (photo at right). Obviously something went wrong with these nuts during nut expansion but what that something was I haven't got a clue. Its just a good thing that we found only these two deformed nuts in the tens of thousands pounds of pecans we have cleaned.

Friday, January 17, 2014

Mid-winter pecan harvest

    It looks like mid-January will represent the longest stretch of harvesting weather we've going to get to pick up the 2013 pecan crop. This past week the Neosho River bottom was humming with the sound of pecan harvesters (photo above). At the Pecan Experiment Field we finally finished picking the entire grove and have now started on our second picking.
   You would think that we could get the majority of nuts picked up on the first pass across the orchard, but several trees have required a second shake to bring all the nuts down. And frankly, mechanical harvesters always leave nuts behind during the first harvest. How much do we harvest on the second pass? The chart below provides some numbers.

    At the Experiment Field, we have 6 native pecan plots that we record annual yield. These plots are labeled A through F and we record the weight of clean, harvested nuts from both the first and second harvests. In 2013, the plots averaged 1640 lbs/acre in total harvest. A little over 20% of that yield was collected from the second harvest.  

Wednesday, January 15, 2014

Seed source for northern pecan rootstocks

    Its the time of year for stratifying pecan seeds. Most northern pecan growers understand that cold hardy rootstock trees are produced from seeds of northern pecan cultivars. Graft a northern pecan cultivar on a southern pecan rootstock and you may find that the tree below the graft union will freeze during a test winter.
    Over the years, we have used several seed sources to grow trees among them Giles, Kanza, Posey, and Colby (photo above). For years, Giles has been recommended for northern growers but why?  Is it really better than other northern seed sources?  Is there a better northern seed source?
   Whenever you plant pecan seeds, the trees that germinate can be very variable in terms of  vigor and disease resistance. Planting a known cultivar only guarantees you know the female parent--the male parent just flew in on a spring breeze. So in choosing a northern pecan cultivar to plant, its best to collect seed from a northern orchard where all possible male parents have a high level of cold tolerance.
    Now lets talk cultivars. The photo above shows a cross section of four pecan cultivars we have used as seed for nursery trees. Note how the Giles seed is poorly filled as compared to the others. Poorly filled Giles kernels are all too common because this cultivar is susceptible to both over-production and pecan scab (both problems reduce kernel quality).  Even if a pecan is poorly filled, the seed can still germinate and grow into a tree. However, seedlings from poor quality nuts have low seedling energy and struggle to grow in height and girth especially during the first year. Slow seedling growth rate translates into a longer wait to graft and a longer wait until nut production.
   Giles seeds also have a hidden defect not easily recognized. Pollen shed and pistillate flower receptivity overlap in Giles. This overlap leads to partial self-pollination and the production of nuts that, when germinated, demonstrate in-breeding depression.  In the nursery, self-pollinated nuts show up as "runts" and Giles seems to produce more runts than other northern seed sources.  Slow growth rate and an excessive number of runts has made me abandon Giles as a seed source for my nursery trees.

Kanza seedlings
    What seed source do I recommend? Kanza and Posey seeds generate aggressively growing seedlings under commercial nursery conditions. Colby seeds grow well but seedlings seem to have a higher degree of susceptibility to disease, requiring greater reliance on a season long fungicide program.
   Last summer, I grew out a couple hundred Kanza seedlings (photo at left). For the most part I was pleased with the results but still had to cull out the occasional runt. Heartlessly culling out under-performing seedlings will leave you with uniformly-vigorous rootstock trees that preform well when planted in the field.  A genetically strong rootstock increases scion growth rate and decreases the wait until nut production.

Tuesday, January 14, 2014

Stinkbugs create a nasty suprise

Leaf-footed Bug
    This past fall the Kanza trees I planted near my home produced their first big crop of pecans. So many nuts in fact that the wife and I decided to harvest the nuts for our own use. Yesterday, I finally got around to cracking our Kanza crop and was disappointed by the number of nuts that had been attached by stink bugs. However, the amount of damage I found was very typical for back-yard, unsprayed pecan trees. There are numerous species of stink bugs and leaf-footed bugs (photo at right) that feed on pecans but all species leave behind bitter-tasting, black spots on the kernel. 
    The photo at left illustrates the type of damage I found caused by stink bugs. The nut on the far left was attacked during the water stage of nut development causing nut fill to cease and the entire kernel to become black and papery. The three other nuts were attacked after the nut had entered the dough stage. Each black spot on the kernel represents a stink bug feeding site.
    Stink bugs are a serious problem for back yard pecan growers. At the Pecan Experiment Field we use pesticides and an air-blast sprayer to keep these kernel feeding pests at bay. But these restricted-use pesticides and the equipment needed to apply them are generally not available to to the small scale pecan producer.  Carbaryl insecticide is widely available to home-owners and is recommended for use to control pecan weevil.  Carbaryl sprays, aimed at pecan weevil, will help reduce stink bug injury but will not eliminate the problem.
    You will notice that the amount of stink bug damage will vary widely from year to year. This is largely due to weather patterns that influence insect populations and the availability of alternative host plants for stink bugs to feed and reproduce.
    One thing is for sure, I'll be picking out a lot of stink bug damaged nuts while I'm shelling out the Kanza nut I picked up at home. 

Thursday, January 9, 2014

Stories behind a few pecan cultivars

    I think every pecan grower dreams about finding a new pecan cultivar,  preferably a tree that grows from a seed he planted. Many of the northern pecan cultivars propagated today are either selections from native pecan groves or chance seedlings planted by a pecan enthusiast.  Today, I'd like to share with you a couple of stories behind three pecan cultivars.
    I met Ed Yates back in 1988 at his farm in Southern Indiana outside the small town of Chrisney. After driving through miles and miles of Indiana corn and bean fields, I came to Ed's farm and found neat rows of mature pecan trees growing on the rolling landscape. The first thing I noticed was a dead crow hung from a low lying tree branch. Ed quickly informed me that he was at war with the pesky varmints. He claimed that tying dead crows up in the trees helped to deter other crows from stealing his pecans. Ed had a nice orchard populated with the more popular northern cultivars of the 1970's; Major, Posey, Giles, and Greenriver. During our visit, he did not share with me the fact that he had planted dozens of seeds from his grafted trees in the hopes of discovering the next great pecan cultivar. It wasn't until after Ed had passed away that I found out members of the Kentucky Nut Growers Association had started to propagate several of Ed's seedlings. Today, we are evaluating Yates 68 and Yates 137 at the Pecan Experiment Field.

   When I look at these two cultivars from Ed Yates, both nuts have a distinctive "Posey" look to the size and shape. Both nuts high percent kernel with Yates 68 producing over 55% kernel and Yates 137  over 60% kernel. The kernel color and quality of Yates 68 looks to be excellent, reminding me of Major or Greenriver kernels. In sharp contrast, Yates 137 has the dark kernel color we usually associate with Posey. Dark kernel color is a major problem for a pecan cultivar because  marketing a nut that appears to be rancid is extremely difficult. 
   I first met Bill Totten at a Northern Nut Growers Meeting back in 1983. Bill was an active member of a team of Illinois pecan enthusiasts searching the Upper Mississippi River bottoms for great, early-ripening northern pecans. About ten years ago he sent me a sample of a nut from a seedling tree he had growing near his home in Alexis, IL. He called the nut "Hark", and I was very impressed by the kernel quality and high percent kernel (>56%). He sent me some scions later that spring and we grafted "Hark" at the Experiment Field for advanced testing.
   I asked Bill about the history of Hark and all he could remember is that he had collected the seed nut from an orchard of pecan trees growing near Moberly, MO.  Is it a seedling of an established northern pecan cultivar? Yes, most likely, but which northern cultivar is hard to guess by looking at the nut. 
   It takes 13 to 20 years for a seedling pecan tree to bear nuts. Planting seeds in the hopes of finding a superior pecan cultivar is a fun but not very profitable venture. The vast majority of seedling trees will produce nuts inferior to the seed parent. However, we are fortunate to have a few dreamers like Ed and Bill that attempt to beat the odds.