Wednesday, April 26, 2017

Tips for grafting pecans with the 3-flap graft

   The weather the past several days has been great for grafting pecan trees. There is nothing better that spending time outdoors carving scions and placing grafts. In a previous post, I've documented how I make a 3-flap graft but this year I took some photographs that I hope will shed additional insights into using this grafting technique.

    I use the 3-flap grafting technique exclusively on small pecan trees. The tree pictured above (on left) had a single stem and was about four feet in height. To encourage the tree to accept my graft, I cut the stock tree down to about 1/3 of its original height (above, right). Whenever I'm grafting, I always remove a significant portion of the stock tree's top growth to encourage the tree to accept the scion.
    In the photo above, I'm holding the top portion of the stock tree I removed before grafting. As you can see, new shoots were emerging from tree indicating the the bark will slip and the time was right for grafting. In addition, my finger is pointing to the annual growth ring on this tree that marks the spot where growth started the previous growing season. The tree put on two feet of new top growth last year which indicates, to me, that the stock tree is ready for grafting and will force the scion to grow vigorously this summer.
     In choosing a scion for a 3-flap graft, I try to match the diameters of scion and stock as closely as possible (photo at right). If I can't find a perfect match, I find it best to use a scion that is slightly larger than the stock (no more that 1/8 inch bigger).

  One step in the grafting process that is easy to forget is trimming the bottom of the scion back to fresh green wood. In the photo at right (top photo), you can see what the bottom end of the scion looks like when taken out of the cooler. I always make sure to clip off about a quarter inch of wood off the end of the scion to reveal fresh, green wood (lower photo at right) . Remember, only living cambium tissue on the scion will unite with cambium tissue on the stock.
    When it comes time to carve the scion, folks always ask me how long to make the peeling cuts. My answer has always been to let the dimensions on my hand determine the cut length. To start the cut, I always place my thumb on the bottom  of the scion. Then, holding the knife firmly in my fingers, I stretch my hand outwards and place the knife blade on the scion (photo at right). I start the peeling cut at this point and remembering to move my thumb off the scion as I cut downwards. In all my of years of grafting, my hand has always been the same size and, as a consequence, all the cuts I make on the scion will be exactly the same length.
    In carving the scion for a 3-flap graft, it is very important to cut deep enough to see white wood in the center of each cut surface. In making the three cuts,  it is also important to make those cuts equidistant around the scion (photo at left). A properly cut scion should have 3 sides cut down to the wood with a strip of bark between each cut surface. Carving the scion correctly is critical for grafting success.  Most 3-flap graft failures can be traced back to not cutting deep enough to expose cambium or cutting off all the bark thus removing all the scion's cambial tissue.
    Inserting the scion into the stock and securing the flaps over the scion often causes frustration among novice grafters. I've discovered an easy way to complete this step without the help of a third hand. Before inserting the scion, I start wrapping grafting tape around the stock tree starting just below the base of the flaps. As I wrap upwards, the flaps are pulled together forming a tube of bark. At this point, I can hold the tape in place and use my other hand to insert the scion. The bark tube will seem a little small for the scion but that's good. Once I push the scion all the way down to meet the wood of the stock, the bark tube will hold the scion in place (as long as I keep holding the grafting tape tightly). At this point, I can continue wrapping the graft union without having to hold onto the scion. The graft wrapping process is pictured above.

   After wrapping the graft with tape, I cover the graft union with aluminum foil and a plastic bag. The next step I take is to prevent wildlife damage to the graft. In the past, I always attached a bird perch to the graft to prevent scion breakage by birds. However, deer have become such a big problem in my area that I am now placing a cage over each young tree and new graft (photo at right). Left unprotected, browsing deer will eat shoots emerging from a new graft and usually break off the scion in the process. The deer cage has the addition benefit of protecting the tree from perching bird damage (birds prefer to perch on the cage instead).  As you can see in the photo, I'm still attaching a bamboo stake to the tree to serve as a training guide once the scion starts to grow.

    As I was grafting trees, I noticed a small unprotected pecan seedling that had been chomped by a passing deer (photo at left). Deer simply love the taste of emerging pecan shoots. This tree will recover and grow more leaves this summer but I will also need protect the tree with a deer cage to make sure this seedling grows strong enough to accept a graft in future years.

Wednesday, April 19, 2017

Choosing where to graft a pecan tree.

    Most of my pecan trees have budded out about a week ahead of their average date of spring leaf burst. So this evening I gathered all my grafting supplies, a box full of scions, and headed for the field to apply my first grafts of the 2017 growing season.
    The first tree I came to was a little over six feet in height with a top divided into three main branches (photo at right). For some, this tree would provide the prefect opportunity to place a 3-flap on each of the branches in an effort to increase the likelihood of obtaining at least one good graft. However, grafting close to the top of a tree actually increases the probability the tree will reject the grafts and simply grow around the scions.
   When grafting trees of this size, I cut the tree off leaving the main trunk about two feet tall (photo at left). You might cringe at the thought of cutting the tree back so far, but I look at it as forcing the tree put all its root energy into the scion that I will place on the stock tree. In addition, I often choose to graft to trees at this height so I can sit on my cooler and graft comfortably. I can certainly graft more trees in a day if I'm comfortable when carving scions.
    I used a bark graft to attach the scion to stock (photo at right). As my usual custom, I then attached a bamboo stake to the tree to protect the scion from bird damage and provide a place to tie up the scion's new shoots to prevent wind damage.
   Because I removed so much of the top of the stock tree, this scion will grow with a lot of vigor. I'll trim the scion down to a single shoot about 4-6 weeks after grafting. The combination of vigorous growth and a single shoot will make training this new tree to a central leader shape very easy.
    The final step in grafting this tree was to place a deer cage around the tree (photo at left). The local deer herd loves the taste of emerging pecan leaves and I definitely don't want all my grafting efforts to be destroyed with a single bite.

Tuesday, April 11, 2017

Pecan trees breaking bud

From L to R: Hark, Major, Giles, Faith (11 Apr 2017)
    Over the past week, our pecan trees have started their spring flush of new growth. At this early stage of bud growth, differences among pecan cultivars are clearly evident. The photo above shows four protandrous cultivars with bud development that ranges from bud swell (Hark) to an early phase of leaf burst (Faith). This arrangement of twigs also reveals that the catkins of protandrous cultivars seem to burst out of their buds before leaves start to unfurl.
    In contrast, the photo below shows 5 protogynous cultivars with a range in bud stage. The buds on the Goosepond twig are just barely getting started while the Lakota twig has leaves unfurling. Once again the flowering habit of these cultivars is clearly displayed. At this point, catkins of protogynous cultivars are still hidden inside their buds and won't start to emerge for several weeks.   

From L to R:Goosepond, Colby, Kanza, Surecrop, Lakota (11 Apr 2017)

Protandrous Faith vs protogynous Lakota
    The photo at right, illustrates the clear difference between protandrous (early pollen shedding) and protogynous (late pollen shedding) cultivars. If you every want to discover the flowering habit of a seedling pecan tree, this early stage of bud break is the best time to make a positive determination.

Monday, April 10, 2017

Pecan bud break influenced by soil type

    The buds of my Kanza trees are beginning to show some life. However, I've noticed some differences in the timing of bud break among my trees. The photo at right shows two Kanza twigs collected on the same day (10 April 2017) and growing only 500 yards apart. The only difference between these two trees is the soil that supports their growth.
    The twig of the left comes from a tree growing in an Osage silty clay. In contrast, the twig on the right is from a Kanza tree growing in a Cherokee silt loam. Both soils originated as river deposited sediments. The Osage soil is a true river bottom "gumbo" soil while the Cherokee soil is a lighter textured second bottom soil.
    The greater the clay content of a soil, the slower that soil warms in the spring. Cold soil inhibits the growth of new roots and with slower root activity bud break is delayed.

Tuesday, April 4, 2017

Cleaning up a bark graft

   Whenever I graft a tree, I usually return to the new graft every 3-4 weeks throughout the summer to prune off trunk sprouts and root suckers. I also like to start training the new scion to grow a strong central leader. The photo at right is an example of a successful bark graft that I made last year but totally overlooked the all summer training. You'll even note that the graft union is still wrapped in aluminum foil and plastic. To get this tree back into shape, I needed a chainsaw, pruning saw, and hand shears.  
   The first step in cleaning up the this young grafted tree was to cut off all the root suckers with a chainsaw and use the hand pruning saw to remove the trunk sprouts. With just these few cuts I've already reclaiming my grafted tree (photo at left). 

    When I grafted this tree last year, I placed a single scion under the bark of the stock tree. At that time, the stock was about 3 inches in diameter  (photo at right, grafting knife set on trunk for scale). Once the graft took, the scion grew vigorously sprouting numerous new shoots. Unfortunately, none of the shoots from scion produced a strongly dominate central leader. This  scion needed pruning desperately to carve out a single tree trunk.

    In pruning the scion, my first step was to trim the stock at an angle to encourage rapid wound closure. To make the cut, I used a small chainsaw to cut the stock tree at a angle of between 30 and 45 degrees (photos above). Not only does this angled cut enhance  healing,  it also encourages water to run off the wound, promoting rapid wood drying and helping to inhibit wood rot.

  Next, I used my pruning saw and clippers to prune the scion into a single shoot (photo at left). Later this summer, I'll need to train this one remaining stem to grow into a strong central leader tree. By removing all of  root suckers, stump sprouts, and more than one half of the scion's shoot growth, this tree will have a lot of pent up energy to sprout new growth come this spring. I will definitely need to revisit this tree with my pruning shears on a regular basis (every 3 weeks) to direct all new growth in the right directions. I'm positive that new trunk sprouts and root suckers will try to grow this summer. But this time,  I'll be quick to prune them as soon as they develop.

   The photo above gives you an idea of what the tree looked like before pruning and then after I had carved out a central leader. At this point it looks like I've pruned the tree into a telephone pole. However, I assure you, that with proper directive pruning, lateral branches will form and the tree will begin to fill out.

Wednesday, March 29, 2017

Sapsuckers have arrived

  Every spring, yellow-bellied sapsuckers stop to visit our pecan trees on their flight northwards. Long before the buds of pecan trees start to break, these members of the woodpecker family will drill a series of holes in the trunks of pecan trees (photo at right).  The holes are dug deep enough to allow rising sap within the tree' trunk to leak out. The sap provides nourishment for the birds as well as attracting insects to the sugar rich sap. When the sapsucker returns to it's freshly dug holes, the bird will dine on both sap and insects.
   Looking at the photo at right, you can see a row of freshly drilled holes in the bark. But six inches above that row is a row of old sapsucker holes that have been closed over by growing bark tissue.
   Sapsuckers holes may look bad but they do not damage nut production.

Monday, March 27, 2017

Counting pecan wood rings

    Whenever we remove trees during an orchard thinning process, I like to stop for a minute and look at the rings in the wood. Each year pecan trees lay down a new and unique layer of wood tissue. Take a closer look at the rings of a tree and you'll discover a little bit more about how a tree grows. During the spring flush of growth, new wood tissue is created with numerous large vessel cells (large pores in the spring wood pictured above). These large vessels are needed to transport the massive amounts of water and nutrients required to build the spring flush of leaves and new shoots. As shoot growth ceases by early summer, demand for water and nutrients slows and the tree creates wood tissue with only small vessels (summer wood pictured above). Small wood vessel cells may not be able to conduct large volumes of water but their small diameter makes it easier to move water up the trunk during the dry summer months.  

  The annual growth rings within a tree's trunk also offer a historical record of past growing conditions. The wider the growth ring and better that year was for tree diameter growth. The photo above shows the growth rings I found inside a Kanza tree we recently removed during a tree thinning operation. During the years 2014-2016 we experienced excellent weather for pecan tree growth--adequate rainfall and plenty of sunshine. The Kanza tree responded to these good growing conditions by at a creating wide, healthy growth rings.
    But look at the rings laid down during the dry years of 2011-2013. Wood growth during these hot dry seasons was stunted by poor growing conditions. In addition, the number of large vessel cells within these growth rings are severely limited (a response to drought). These large vessel cells are also stained dark brown (especially the 2013 wood). When a pecan tree suffers from drought, the large vessels stop working and the tree plugs up the non-functioning cells to preserve water within the tree.
    Next time you remove a pecan tree, take a little time to read the story left behind in the growth rings. I always seem to learn something new.   

Wednesday, March 22, 2017

Pecan trees still waiting for Spring

    With temperatures hitting the 80's (>27 C) a few days ago, everyone is talking about Spring arriving early this year. So today, I went out to the pecan grove to see if I could find any signs of bud growth on our trees. The vast majority of pecan cultivars I inspected were still fully dormant. The Pawnee and Posey twigs pictured above are just two examples of cultivars with dormant buds. On the other hand, Mohawk buds have started to split open the outer bud scale (crack in the scale marked by red arrow). To get a closer look at the Mohawk bud click on the photo for a full screen photo.
   Outer scale split is the very first indication of pecan bud swell. It also marks the time when pecan roots start their spring flush of new growth. In just a couple of weeks we should see all pecan cultivars start bud expansion. In five weeks time, I'll be grafting trees.

Monday, March 13, 2017

Narrow crotch tear-out

     The other day, I spotted a young tree in my orchard with a wind-torn branch (photo at right). At first, all I was thinking was, "how did that happen?". But then, as I approached the tree, I immediately recognized the cause of the break--a narrow  crotch up in the center of the tree that I somehow missed during earlier pruning trips through the orchard. Just a month ago, I wrote about the importance of pruning out narrow "V" crotches to ensure that limbs don't tear out during wind storms. I guess its time to go back through the orchard again to make sure I didn't miss other narrow crotches.
    A closer look at the damage reveals that the tree basically split in two, right down the center of the tree (photo at left). At the top of the wound, you can see a bark inclusion that forms between the two halves of a narrow crotch. Under the pressure of strong winds, narrow crotch split apart and then one side ripped down the trunk for about 12 inches.
   I pruned off the bent and fractured limb and I left what was left of the central leader in place. Sometime before this tree breaks bud and grows a new crop of leaves, I'll need to place a brace up in the tree to prevent the weakened central leader from breaking over. I'll attach the brace to the tree using duct tape and keep the brace in place until the central leader grows enough wood to support itself (probably 2 years for this size tree).

Wednesday, March 8, 2017

Spreading fertilizer on the pecan grove

   With rain predicted at the end of the week, we decided to spread a little fertilizer on our pecan grove today. We spread 150 lbs. of urea (69 lbs nitrogen) and 100 lbs. potash (60 lbs. potassium) on each acre of our orchard. With this volume of fertilizer, its going to take us a little while to cover the entire Experiment Field.
   Today's fertilizer application is the first part of our regular fertilizer program. We apply fertilizer twice per year every year. During early March we spread nitrogen and potassium. Then, in October, we'll make an additional application of nitrogen. In total, we are adding 115 lbs of nitrogen and 60 lbs of potassium to our trees annually.

Thursday, March 2, 2017

Anatomy of the branch collar

   Every time I talk about pruning off low limbs from pecan trees, I end up describing how to make the proper pruning cut. Typically, I've talked about removing a limb by cutting just outside the branch collar (photo at right). Removing limb in this manner promotes quick healing, reducing the spread of wood rotting organisms. But is there an anatomical reason this pruning method works so well? Let's look under the bark to see.

    Last summer I cut a pecan sampling and carefully pealed the bark off the main stem and all the side branches (photo at left). After drying, the patterns of wood grain formation really became pronounced. You can see a raised branch collar formed by wood fibers that flow vertically around the side limb. By cutting limbs off outside this collar you don't disrupt the flow of water and nutrients from the roots to the upper portions of the tree. Cutting into the collar causes a disruption to sap flow and  creates a wound that takes much longer to heal.

Monday, February 20, 2017

Thinning more Kanza trees

      For the past six years, we have been progressively thinning a three acre block of Kanza trees. This week, we removed trees within the Kanza block in areas where adjacent trees were competing for sunlight and according to our thinning plan (photo above).  During this sixth year of thinning, we cut down 15 trees; the most we've removed in a single year. The original tree planting had 144 Kanza trees. After removing 15 trees this year, we'll be down to 96 trees in the orchard.  The first thinning will be complete when half the trees have been removed and we are down to 72 trees in the 3 acre orchard.  

    The figure at right is a map of the Kanza block as it appeared before we cut any trees this winter. Each tree is depicted by a green circle with a diameter proportional to the tree's trunk diameter. As you can see, tree growth has not been even across this orchard. Tree growth has been fastest in the northern 1/3 of the orchard.  As a result, we've thinned more trees in this area of the orchard. However, trees in the southern half of the orchard continue to grow and will require thinning eventually.

    We removed 15 trees from the Kanza Block this year.  Trees cut down are marked by black circles on the map at right. We thinned trees over the entire planting but most removed trees were located in the middle third of the orchard.
   Up to this point, I've been pleased with this progressive approach to orchard thinning. By taking out trees on an as-needed basis, we have been able to maintain good light penetration into the orchard while preserving high yields

Thursday, February 16, 2017

Pecan tree limb pruning and collecting scions

    On a mild sunny days in February, its hard for me to stay indoors when there are pecan trees to prune and scionwood to collect. When approaching a young tree, like the one pictured at right, I confine my pruning efforts to removing low limbs and removing serious structural problems. And, because I'm pruning young trees, the limbs I cut off usually produce some excellent scionwood. Let me take you through the process. 

    I started by removing the lowest limb on the left side of the tree pictured above. When removing low limbs, always cut back to the trunk but make that cut outside the branch bark collar.
    The photo above shows the tree before and after pruning. The side limb I removed looks like it was growing out of a socket in the main trunk. The raised bark area on the trunk that forms that socket is what we call the branch bark collar. I plunged the blade of my chainsaw into the side of the limb just outside the collar and dropped the limb off the tree. Leaving the branch collar intact will help the tree quickly heal over the wound.

    I moved over to the other side of the tree to prune off the next lowest limb on the tree. With this limb, the branch bark collar is not so obvious. In the photo at right you can see a slight swelling of the bark around the limb where it attaches to the trunk. The place to prune off the limb is marked by the red dashed line. The final cut is shown on the far right.

    My goal in pruning off lower limbs is to make working around the tree easier. In the photo at right, you can see that removing just two limbs makes a big difference in terms of improving access for orchard operations like mowing, herbicide application and harvest.

    Besides cutting off lower limbs, my dormant season pruning routine also includes looking for potential structural problems. One common problem is the development of a V crotch (circled in yellow in photo at right). Left to grow, a V crotch will form a bark inclusion between the two branches increasing the likelihood of branch tear out. So while the tree is still relatively small, I reached up and cut off one of the two branches that had formed the V.  After taking out the V crotch the tree might look unbalanced but it will quickly fill the open space in the canopy with new shoot growth.

    I also look to remove branches with narrow crotch angles and deep bark inclusions. The method I use to cut out these narrow angled branches depends on the size of the limb. Previously, I showed you how I cut out a larger limb using the three cut method. With the 2.5 inch side limb pictured above I made just 2 cuts. The first cut I made was and undercut about 1/3 the way through the branch. I made this cut at an angle that would promote rapid wound healing. Next I used the chainsaw to plunge cut into the side of the limb to remove the limb.

    The young trees I pruned were growing rapidly so the branched I removed held many one-year-old shoots that were over 2 feet long.  Before hauling the pruned limbs off to the brush pile, I cut off any shoot that wase 3/8 inch or larger in diameter. Some of the wood I collected is shown at right.

    In collecting scions, make sure to collect only last year's shoot growth. Sometimes on young trees its a little difficult to tell where 2-year wood stops and 1-year wood begins. In the photo at left, the yellow arrow points to the annual growth ring which is the point on a shoot that marks the beginning of a new shoot growth year. Above the growth ring is 1-year wood. Note the large primary buds on the 1-year shoots. Below the growth ring is 2-year wood. Note that the primary buds on 2-year wood are gone. They either dropped off the tree or sprouted last year to produce catkins. Either way scionwood without strong buds is useless.

   In cutting scions, I usually cut the wood into 7 to 8 inch long pieces, making sure I have at least 2 good buds on the upper half of the scion. In cutting up the wood, I also like to make sure the lower half of the scion is straight. Looking at the shoot pictured at above I noticed a strong curve at the base of the shoot. I cut off the curved portion of the shoot and discarded it. Right above the curve I cut out a perfect piece of Kanza scion. 

    In cutting scions, I also look for scars or imperfections in the wood. Since I'm collecting scions from low limbs, I find that some branches get banged up by the tractor when I mow the orchard. I always cut out imperfections like one pictured at left. There is usually plenty of good scions to be found above and below such a branch wound. 

Tuesday, February 14, 2017

Kanza yield 2016

   As most readers of this blog will know, I am a big fan of the Kanza pecan (photo at right). At the Pecan Experiment Field we have a 3 acre block of Kanza trees that was established when we planted nuts in the field to produce rootstock trees back in 1996.  These seedling trees were then grafted to Kanza during the years 2000-2003. The original planting contained 144 trees but since 2012 we have been removing trees as adjacent trees start to crowd. My goal was to maintain a high level of nut production while preventing tree over-crowding. I outlined this gradual thinning plan in a blog post back in 2012.
     By 2016, we have removed 33 trees, yet total yield per acre has increased (table below). Yield was negatively affected in 2011 and 2012 by intense summer droughts and small nut size.
     We saw the first indication of Kanza over-producing in 2016, so I expect a drop off in yield in 2017.  In addition, I've marked 15 trees in the Kanza block for removal this winter. Can the remaining trees make up for the lost production from thinned trees?  I guess we'll find out come next fall.

Tuesday, February 7, 2017

Pruning top-worked pecan trees

    Back in 2014, I decided to top-work some young trees to new cultivars. In previous posts, I wrote about the grafting process and training those new grafts.  Because these trees were fairly large when I placed a bark graft on the central leader, I left several lower limbs on the tree to provide critical leaf area to keep the tree actively growing. For the past 3 growing seasons, I've pruned back the growth on limbs below the graft to encourage growth of the new scion (graft union painted white--photo at right). At this point, the tree's new top has begun to fill out and I can safely start removing limbs below the graft union.
   The tree pictured above was easy to prune. I simply removed the two largest low limbs (photo at left). This left me with a couple of small diameter limbs under the graft union but I'll leave those on for now. One of the disadvantages of top-working a tree this size is how quickly it grows in height. It becomes increasingly difficult to train a central leader 15 feet up in the air. As the new growth begins to burst forth this spring, I'll  get out my 8 foot orchard ladder and practice some directive pruning on the top of this tree.

    The next top-worked tree I needed to prune presented more of a challenge (photo at right). This tree had four strongly growing limbs growing under the graft union (graft union painted white). In fact, it looks like the lower side limbs are actively competing with the scion and slowing the growth of the new top.

   The problem with this tree is that 3 of the 4 limbs growing below the graft union are attached to the trunk adjacent to each other (photo above left). Pruning all these limbs off at one time would leave almost two thirds of the trunk's diameter without bark--limiting the ability of the tree to transport nutrients to the scion. I decided to remove just two of the limbs this year (cuts marked by yellow dashed lines). I'll let the tree callus over these two wounds before I remove the remaining limbs under the graft.

   To help further promote the growth of the scion, I pruned back some of the growth on the remaining low limbs (photo at left). Then, over the course of the summer, I'll continue pruning back the side limbs that are growing out from below the graft.
    The one large side limb I left on the tree will definately try to outgrowth the scion. It will take monthly summer-pruning sessions to keep this limb in check. By mid-summer, I'll probably have this limb cut back to half its current length. In one or two years, the entire limb will be removed back to the trunk.