Wednesday, March 14, 2018

Big native pecan tree weakened by wood rot

    Last harvest season, I came across a tree (photo at right) that I was scared to shake. From a distance it just looks like is a big old native tree that bears the scars of the 2007 ice storm (numerous sprouts from chopped-off limbs). It was only when I went to clamp onto the tree that I noticed a large crack in the trunk. I carefully shook the tree in December  but made a mental note to remove the tree come late winter.

    The trunk of this native tree had a large crack running over eight feet in length (photo at left). I looked inside the crack and discovered a rotten cavity inside the core of the tree. This tree was a potential disaster waiting to happen so I decided to cut it down.

    Cutting down a hollow tree can be tricky. The structure of the tree is so weak that you can't predict when or how the tree will fall once you start cutting. I had cut only one quarter around the trunk, when I heard the sound of wood splintering and cracking. I pulled out my chainsaw and moved away from the tree to watch it come crashing down. It was not the prettiest way to fell a tree but at least this potentially hazardous tree was on the ground (photo at right).

    The way the tree split apart upon falling allowed me to photograph the internal structure of the wood. I've labeled the key portions of the tree trunk in the photo above. Starting at the far left is a very normal looking layer of bark. Inside the bark are multiple layers of white sapwood. The heartwood of this pecan tree is reddish brown. As I looked to the center of the tree I came across a portion of the heartwood that was riddled with the white hyphae of a wood-rotting fungus. Fungal decay of the heartwood caused it to become soft and lighter in color. The hollow core of the tree represents the portion of the wood that has been completely broken down by fungal activity.    

    Inside the hollow core of the tree, I found the fruiting body of the wood-rotting fungus (photo at right). This fungus is a member of a mushroom family commonly referred to as shelf fungi. The fruiting body of this mushroom is hard and feels woody. Rather than gills, the underside of the shelf fungus has numerous pores that release spores. The appearance of shelf fungi on a tree is sure sign of significant internal wood rot.

Wednesday, February 28, 2018

Thinning a Kanza Block:

    Over the course of the last 6 years, I've documented how we have progressively thinned a 3-acre block of Kanza trees (photo at right). In 2012, I drew up a tree thinning plan and have removed trees only within areas of the orchard with tree crowding. Year after year the trees continued to grow. As adjacent branches started to touch, we cut more trees. You can review the history of our thinning plan and the progress we made removing trees over the past 6 year by checking out the links listed below. 
1. 2012, 2013, and 2014 tree thinning 
2. 2015 tree thinning
3. 2016 tree thinning
4. 2017 tree thinning

     Following the 2017 pecan harvest, we measured the diameter of each tree's trunk and plotted that data on the map pictured at left. Each tree in the orchard is designated by a green circle with the size of that circle directly proportional to the diameter of the trunk. As you can see from the map, the bulk of the trees that still need removing are located at the south end of the field. You will also note that the largest trees in this orchard are located in the northeast corner. If you review the history of our progressive thinning plan, you'll find that we started the thinning process in the NE corner of the orchard back in 2012.
   This year we completed the thinning plan by removing 23 tree from the orchard. The black dots on the map at left shows the location of the trees removed this winter.
  When this orchard was established from stratified seed in 1996, we set trees 30 feet apart in a square pattern. In 2000, we grafted all 144 trees to Kanza. Now that we have completed our thinning plan, we have 72 trees remaining spaced 42.4 feet apart. The trees are still arranged in a square pattern but the squares are now tilted 45 degrees from the original north-south orientation.
   It won't be too many more years until this orchard will need another thinning plan as the remaining trees continue to grow at the rate of 1/2 inch in trunk diameter per year. The next thinning plan will remove every other north-south row to carve out an orchard with trees 60 feet apart.

Monday, February 26, 2018

Dormant pruning last year's bark grafts

    Finally, the sun came out and it was a great day to get outside.  I hopped into my UTV and drove down to the pecan grove to check on some of last year's bark grafts. The photo a right shows a Kanza graft that grew exceptionally well. The scion produced three strong shoots with the central leader growing over five feet in length in a single growing season.

   However, taking a closer look at the scion, just above the graft union, reveals that I've already got a tree with a narrow fork and a side limb that's growing way too close to the ground. So I grabbed my pruning shears and made a couple of much needed cuts.
    First, I removed the left side of the narrow fork. Then I pruned off the side limb growing out to the right (photo at right). This left me with a single central leader and a good shoot to develop into my main tree trunk.  After pruning, I moved down to the graft union and removed the plastic bag and aluminum foil from the tree.
    With the graft wraps removed, you can see that the graft union has callused over nicely. On the left side of the graft union you can still see the staples I used to attach the graft.   But notice the color of the bark that was once covered by the aluminum foil and plastic bag.  The chestnut brown color of the bark indicates that this bark is not used to being out in full sun and may be prone to sun-scald.
     At this point, I used some cheap latex paint to apply a sun block over the entire graft union (photo at right). I used white paint to mark the tree as being grafted to Kanza. By painting the graft unions, I can quickly see which trees are grafted and which cultivar is grafted on the tree. On my farm, white=Kanza, yellow=Lakota, green=Hark, etc.  It takes a little extra time and money to color code trees but its definitely worth it to help me keep tract of my grafting efforts. It easy to get lost in my pecan orchard because it is based on grafting volunteer seedlings that have popped up at random across the field. No nice straight rows to keep things in order.
   Once I replaced the deer cage over the tree, I noticed that the top of central leader had several small branches that had developed from stalked buds (photo at left).  All of these shoots would develop into narrow-angled branched with deep bark inclusions. So to prevent future problems with limb breakage, I pruned off each small shoot and any remaining stalked buds.
       After pruning the central leader, I was left with a single strong shoot (photo at right). When this tree starts to bud out this Spring, I'll need to return with my clippers to perform some directive pruning to help maintain good structure. Side shoots will  emerge this coming season and my new Kanza graft will start looking like a pecan tree.

Wednesday, February 21, 2018

Reviewing pecan cultivar data

    On cold winter days, its always fun to pour over cultivar trial data. Below, I created a table of nut performance data for 43 pecan cultivars growing at the Pecan Experiment Field. For each cultivar, the table shows the number of years nuts were evaluated (N), the weight of a nut (average, maximum, and minimum), and the percent kernel (average, maximum, and minimum).
     The time period of this data set (2004-2017) represents some of the most extreme weather conditions our trees have survived. We've seen record floods (2007) and record drought (2012). We suffered a limb-breaking ice storm (2007) and late spring frosts (2007, 2014). It no wonder that over the course of 14 years we've recorded some wide swings in cultivar performance.