Saturday, May 26, 2018

New grafts breaking bud

    This year, I started grafting pecan trees in early May. Today, three weeks later, most of my scions have broken bud (photo at right). For me, the grafting process now shifts towards efforts to train and prune the young grafted tree. Starting today, I took steps to ensure that the scion continues to grow rapidly and does not become overwhelmed by stump sprouts that form below the graft union.
   Whenever  I see that I have a successful graft, I prune off all stump sprouts. At this point, stump sprouts are still small and easily remove by just ripping them off the trunk with my hand (photo at left).
    More stump sprouts will probably appear later this summer, but for now, all the tree's energy will be focused on growing scion shoots (photo at right). I like to visit my new grafts every three weeks during the summer to prune off stump sprouts and to train the scion to form a new central leader. 

Thursday, May 24, 2018

Nut set after a late spring freeze.

     Between rain showers this week, I took a closer look at pistillate flower production on many of the cultivars in our collection. Back in early April, we experienced some some late Spring frosts that caused a lot of damage to terminal buds. The photo at right illustrates the typical response our trees have made following the April deep chill. The terminal buds on last-year's-wood were killed and never opened (red arrow points to dead buds). However, primary buds have grown from the mid-portions of the shoot and some of those have terminated in a cluster of female flowers (inside yellow circle).

     I looked at about 15 cultivars including short-season northern cultivars as well as full season southern cultivars. I found the same type of growth and flowering patterns among all cultivars. Trees are producing nut clusters on shoots that originate from mid-shoot primary buds. However, the number of nuts in a cluster seems fewer than normal; 2 or 3 nuts rather than the usual 4 to 5 (nut cluster in yellow circle at right). I also noticed that many new shoots did not produce pistillate flowers at all. Then end result of this year's late Spring freeze will be a below average nut crop come this Fall. 

Saturday, May 19, 2018

Pecan pollination season

Faith female flower cluster 2018
   I finished up all my grafting projects last week just in time to record the flowering habits of all the trees in my pecan breeding plot. On Saturday, all the protandrous cultivars had already shed their pollen while pistillate flowers on these trees were only now becoming receptive. In contrast, trees with the  protogynous flowering habit had pollinated female blooms with catkins that were still not releasing pollen.

    Lets look at two cultivars to see the differences between protandrous and protogynous cultivars.  I'll start will Kanza, a protogynous cultivar. The photo at left shows a cluster of Kanza female flowers. Note that the stigmatal surface of each flower is tinged black. This is the first indication that these flowers are already pollinated.
    Kanza catkins, the male flowers, are still green (photo at right). Catkins will turn yellow in color just before each pollen sac opens up to release pollen into the air. These catkins will be opening up sometime this week.
     Hark is a protandrous cultivar. In the photo at left, Hark catkins have turned fully brown indicating that pollen sacs have already opened and pollen has been released. Look closely at the catkins and you'll see that each pollen sac is split open and the catkin is almost ready to fall from the tree.
Hark pistillate flowers are not very showy, but as a wind pollinated crop, it doesn't need colorful flowers (photo at right). These Hark female flowers have not yet started to glisten with stigmatal fluid. When a female flowers becomes receptive to pollen the stigma produces a fluid to help capture pollen from the air.
   It takes trees with both flowering habits to ensure a successful pollination season. A protandrous cultivar like Hark was shedding pollen when a protogynous cultivar like Kanza had receptive pistillate blooms. In a few days, Kanza will start to release pollen just in time to land on receptive Hark female flowers.
   Pecan trees  have developed this flowering dichogamy to ensure cross pollination and preserve hybrid vigor within the species. 

Wednesday, May 16, 2018

Decisions in making a 3-flap graft

    Every morning I've been grafting the volunteer pecan seedlings that have sprouted on my farm. Since these "pasture" pecan trees have been mowed over at least one time in the past, most of these seedling trees have multiple stems. I prime example is pictured at right.

    In grafting this tree, I started by cutting off the small spindly shoot below ground level (photo at left).

   The two remaining shoots were perfect candidates for making a 3-flap graft. I selected the largest diameter scion I had in my cooler and held it up to each shoot to judge the locations were scion and stock were roughly the same diameter. The stem on the left was slightly larger (in diameter) that the stem on the right. I soon discovered that a 3-flap graft applied to the left-hand shoot would sit much higher up the stem than one placed on the right-hand shoot (photo above).  

   Given a choice, I have found that cutting off more of the stock tree increases scion growth rate once the scion calluses.  I decided to place my graft on the right-hand shoot and prune off the left-hand shoot (photo at right). Again, I cut off the stem as low as possible.
  You might be wondering why I didn't graft both stems. I find that wrapping the graft becomes a problem when you have another stem in the way. It hard to concentrate on pulling the grafting tape hard enough to compress the bark flaps against the scion when you keep bumping into another pecan shoot.
    Once I cut out the competing stem, I held up my scion to find just the right spot to place the graft (photo at left).

   I always look to avoid making a 3-flap graft on a stem with a pronounced "dog-leg". In the photo above, the yellow arrow points to the spot I plan on cutting the stock tree.  Above the arrow, the stem zigs and zags. However, below the arrow the stem is nice and straight. I always cut the stock tree off at a location that maximizes the length of straight stem.  It is so much easier to create three, even-sized flaps when working with straight wood.

    Once I choose the spot to make a graft, the rest of the grafting procedure was completed using the typical 3-flap grafting method. The photo at right shows the completed graft along with an attached bamboo stake that I'll use for training the scion this summer.

Wednesday, May 9, 2018

Bark grafting tips

    This year Spring arrived late but our trees are finally bursting with new leaves. This also means it is time to get grafting.
 I've been grafting for several days now so I decided to stop and take a few photos to relay a few grafting tips.
    For me, the grafting process begins by sizing up a young sapling pecan tree and deciding which grafting method is best suited for that particular tree. The photo at right shows a small tree that is the perfect size for a bark graft. For a detailed description of the bark grafting technique I use, click HERE for one of my previous posts on the subject.
     I like to be aggressive in preparing the stock tree for grafting. I start by removing any basal sprouts and very low limbs. I then remove much of the remaining top growth to leave a single stem to accept the scion. The height of this cut was chosen because it is a comfortable height for me to work on when sitting on my cooler full of scions (photo at left).  By removing over  2/3 of the top of this tree, I'll be forcing the tree to put all it root energy into sprouting the buds on my scion. 

    If the stock tree has a lot of rough bark, I use a wood rasp to smooth the bark in the area where I plan on placing the scion. Smoothing off the bark makes the remaining bark more pliable and allow for a tighter fit over the scion.  Use the rasp with light touch. Shave off to much and you can cause the bark to tear when the scion is inserted.

   I inserted the scion in my usual way. Note that the bark is already forming around the scion (photo at right).

    Once the scion is fully inserted I always check for gaps between the scion and the stock. In photo "A" above, the yellow arrow points to an air gap between the wood of the stock and the scion. Using my fingers to apply pressure, I can close that gap ("B" above). Air spaces between scion and stock always lead to graft failure. So I use a staple gun to hold everything tightly in place ("C" above).

    Once I cover the graft with aluminum foil and a plastic bag, I always count the number of exposed buds on the scion. If I find more than two buds, I prune the scion down so only two remain (photo above).  I like to limit the number of buds on the scion so that the remaining shoots will grow more vigorously.

    The deer herd in my area seem to have developed a fondness for the flavor of newly emerging pecan leaves. So to prevent any deer browse on my new grafts, I always cage the tree in 2 inch by 4 inch welded wire (photo at left).

Friday, May 4, 2018

Pecan pollination habit revealed at budbreak

     While I was checking pecan budbreak, I cut shoots from two popular pecan cultivars (photo at right). These two cultivars represent the two flowering types pecan cultivars can exhibit. Kanza is a protogynous cultivar, meaning that female flowers become receptive before pollen is released. Hark is protandrous which means that pollen is shed before pistillate flowers become receptive. These two cultivars will pollinate each other. The early pollen shed by Hark will pollinate the early female flowers set by Kanza. Later in the pollination season, Kanza pollen will be released just in time to pollinate the late female flowers on Hark.
    During bud break you can already see clues to the flowering habit of any cultivar. The catkins of protandrous cultivars will be large and fat right at bud break. In contrast, the catkins on a protogynous cultivar at this time of year will be small and thin. One close up look at the photo and you can easily see the difference. Remember, you can click on any photo in this blog to get a larger image of that photo.

Wednesday, May 2, 2018

Bud break after early April freezes

    During the last week of April, we finally received some warm night-time temperatures that have stimulated the buds on our pecan trees to finally push open (photo at right). In my last post, I mentioned that I discovered some freeze damage to buds from the April 16th freeze. Now that the trees are finally starting to grow I can see the extent of that damage.
   The first thing I noticed was a wide degree of variation in bud break over the entire tree's canopy. With some trees, freeze damage was pronounced on lower limbs while higher in the canopy the buds were breaking normally. The photos above are examples of bud break on the same tree. In the lower portion of the canopy, terminal buds were killed and you can see green buds pushing out from the base of last year's shoot. Twenty five feet up in the air, bud break appeared normal.  The difference in damage due to height within the tree canopy is due to the fact that on April 16th we experience a radiation freeze. During these types of freezes, temperatures are coldest closer to the ground.

        I discovered that most cultivars suffered only limited cold damage. On many trees, bud break on lower limbs appear almost normal, except if you look closely, the terminal buds are stunted and not growing normally (photo above). Buds just below the terminal are growing new shoots.This type of damage becomes obvious when you compare the lower shoot to one growing higher in the tree. Note that the terminal buds on the upper shoot are growing strait up from the terminal of last year's growth, just like they should.
    Since the vast majority of nuts are produced in the upper portion of the tree's canopy the impact the the April 16th freeze will be minimal. However, we won't know for certain until pollination season rolls around later this month.