Tuesday, January 29, 2013

Dormant pruning pecan trees

    Many folks that have grown grafted pecan trees become frustrated by the seemingly unruly growth habits of their trees (photo at right). That's why I have developed some simple rules for training young trees that can help you get your trees off to a good start. Sometimes, however, pecan trees seem to just get ahead of your best pruning efforts. That's when I receive photos of trees in my Email accompanied with cries for pruning advice.
   With the spring like weather we had yesterday, I decided to prune a couple of trees and photograph the cuts I made. The first thing you will notice about pruning pecan trees is that every cultivar seems to have it own growth form. So I photo-graphed the pruning of a Jayhawk tree (spreading growth habit) and a Faith tree (upright growth habit).

     Lets start with the Jayhawk tree (photo at left). The first thing you will notice should be that my efforts at directive summer pruning has created a fairly well balanced Jayhawk tree that doesn't require a lot of corrective pruning during the dormant season. However, I have two objectives for pruning at this time of year: Remove a lower limb and remove any branches that are obviously heading in the wrong direction. To illustrate my pruning cuts, I've created side-by-side photos that represent "before" (left side photo) and "after" (right side) shots of the same pruning cuts. Hopefully, these photos will help demystify the art of pecan tree pruning.
     Here's the lower portion of the Jayhawk tree (photo at right). The red arrow points to the lower limb I plan on cutting out. I used a  pruning saw to remove the limb, cutting just outside of the branch collar. In pruning out lower limbs, don't get in a hurry. Remove only one or two lower limbs per year. Take too many lower limbs off at one time and you will end up with a sunburned trunk and massive cambial death on the southwest side of the tree.

  Next, I looked over the side limbs for possible corrective cuts. In the photo at left, the red arrow is pointing to a portion of a side branch that is pointing straight upward. This upward-growing shoot is directly competing with side limbs trying to grow outwards just above. To encourage the outward growth of the side limbs, I made a "bench cut" by removing the upward growing portion of the limb, cutting back to a outward growing side shoot.

    As a tree grows larger, it becomes more difficult to see where you need to make summer pruning cuts. Near the top of the Jayhawk tree, I discovered a side limb trying to outgrow the central leader. This happens frequently when a side limb points due south (towards the sun) just like the limb in the photo (above, right). I should have pruned this limb last summer to direct its growth outward but didn't notice the problem until this winter. I used a pole pruner to make another bench cut. The red arrow points to the limb that needs pruning while the red circle highlights the resulting bench cut.

    My final cut on the Jayhawk tree was to preserve the central leader. At the top of the tree I had two shoots growing straight up. Using the pole pruner I removed one of  the shoots (red arrow, photo at left). There will come a time when my Jayhawk tree grows too tall for pruning the central leader. Once the tree is out of my reach with a 16 foot pole pruner, I'm done trying to maintain a single central leader. Twenty feet of single trunk is good enough!

    Now let's look at the before and after photos of the Jayhawk tree (photo a right). This tree was fairly well balanced before I started and didn't need a lot of pruning. Look carefully and you should note that the central leader is better defined in the "after" photo. That is exactly what I was after when I picked up my pruning tools.

    The next tree I pruned was a Faith tree (photo at left). In the photo, note that the side limbs want to grow upwards instead of outwards. In approaching this tree, I had the same two pruning objectives as before: Start removing lower limbs and remove any branches that are obviously heading in the wrong direction. There is one more thing I like to keep in mind while pruning during the dormant season. I try to take off as little wood as possible because dormant pruning can force vigorous regrowth often in awkward and unexpected directions. This wild regrowth can become an even greater pruning headache.
    I started at looking over the lower limbs (photo at right). The first thing I noticed was that one of the lower limbs was growing strongly upwards (red arrow). Rather than taking the entire limb off all the way back the the trunk, I made a bench cut to outward growing side shoots.

   After making the bench cut, I still needed to remove a lower limb. On the left side of the tree I noticed that I had a limb directly above one of my lowest limbs. I removed the low limb (red arrow) knowing that the upper limb (green arrow) will fill out that side of the tree.

    The upward growing tendency of this Faith pecan tree meant that I spent a lot more time on this tree making bench cuts. In the photo at right, I removed a strongly upward growing shoot (red arrow) by cutting back to some outward growing side shoots. I made many more bench cuts within the canopy of this tree to encourage the growth of the central leader.

    As you can see from the before and after photos (at left), the Faith tree had much more wood removed than did the Jayhawk tree. The removal of just one lower limb and a bench cut on the other low limb opened up the tree considerably. Although not perfect, I hope you can see that the central leader is better defined after pruning that it was before.    
    Don't expect to correct all your trees problems during a single pruning session. The tree will continue to grow and you will need to keep removing lower limbs and pruning limbs growing in wrong directions. Pruning pecan trees is a process that requires patience and a good eye for tree structure. Developing the well-balanced, strong trunk of a mature pecan tree will take years.   


Wednesday, January 23, 2013

Even more deer damage to young pecans

    The local deer herd is driving me crazy. Just when I think I’ve figured out how I prevent deer damage to my young trees, these pesky creatures find a new way to destroy new plantings. This past fall, we planted some small, container-grown seedlings in openings within our native pecan stands (photo at right, tree between yellow flags).  We tilled up a small area of soil and set the tree in the center of the cleared ground. Since the trees were barely 2 feet tall, I didn’t think buck rub would be a problem, so we left the trees unprotected. Within a month of planting the tree, the tilled soil around every tree was covered in deer tracks—an ominous sign (photo above). 

   Later we discovered some of the newly planted saplings ripped out of the ground and laying on top of the soil (photo at left). When I picked up the uprooted tree, I discovered that the very top seedling had been chomped and broken. It seems that our well-tended nursery trees proved to be an irresistible snack for browsing deer. When a deer chomped down on the shoot tip and pulled up to take a bite, the entire tree was lifted out of the loose dirt.  Next time I plant seedlings in the fall, every tree will be protected by a welded wire tree cage (photo below).
Welded wire tree cage

     In a previous post, I showed you the plastic trunk guards we have been using to prevent buck rub. This past August, we installed these guards on some young trees that were about 5 feet tall. The stems of these trees are roughly 1 to 1 ¼ inches in diameter—the perfect size for bucks to rub.  We’ve had good success with these tree guards in the past so once installed around our trees, I thought our deer problems were over. 
    Today, I was out inspecting the grove and discovered the deer had removed several guards and then proceeded to rub the bark off the young trees (photo at left). How did that happen? If you look at the tree in the photo, you’ll note that the tree is just a single stem without and side branches. Most likely,  a buck removed the cage right over the top of the tree while trying to rub the trunk. So here’s another lesson learned from the school of hard knocks. I need to use a welded wire tree cage around trees that are not yet large enough to produce the strong side shoots needed to keep deer from removing the plastic tree guard.

    In our orchard, deer are an increasing problem. Based on this year’s deer damage, I have decided on taking the following steps. 

> Install a welded wire tree cage as soon as a seedling tree is planted. 
 > Switch to a 3 foot plastic trunk guard once the seedling has enough clear trunk to hold the guard and enough stout side branches keep the guard in place.

Plastic trunk guard
    You might ask, why bother with the plastic trunk guard at all, just stick with the tree cage.  Once a tree starts to develop side shoots, branches often grow out through the cage making it nearly impossible to train the tree properly. I recommend a strict regime of summer pruning young trees to shape the young tree (the 2 foot rule) and develop a strong central leader.  So, the sooner you can move the deer protection to just the trunk, the easier tree training will be. I leave the plastic trunk guards in place until trees grow to 4 inches in diameter (photo at right).

Saturday, January 19, 2013

Pecan size determined by soil and available water

     Last summer's drought and high temperatures effected agriculture across the Midwest, including pecan groves. In previous posts, I discussed how drought can effect nut size, influence nut shape, retard kernel filling, and prevent proper shuck opening. Today we were evaluating nut samples collected from several locations and soil types. The differences we found  among four Pawnee samples were astounding and I just had to share our observations (photo below).

    Its almost hard to believe that all four samples were produced by trees of the same cultivar. The largest Pawnee nut was produced in Illinois, growing in a deep silt loam soil and irrigated during the mid-summer drought. The combination of great soil and ample water provides ideal conditions for nut growth and kernel fill.
    The second largest nut was produced in Kansas at the Pecan Field. Last summer we were fortunate to have a flood in May that saturated our heavy clay soils. Our Pawnee trees ended up mining that water later in the summer to produce a smaller but well filled nut. However, last summer's heat and drought did cause some kernel defects on our Pawnee nuts. 
    The two samples from Missouri were collected from trees growing at the Horticulture and Agroforestry Research Center in New Franklin. Central Missouri was hard hit by the 2012 drought, decreasing nut size significantly. These samples provide a great example of how site and soil type can effect nut production. The tree growing in the silt loam soil is actually located in a very fertile and moist creek bottom. Trees in this planting have grown exceptionally well with many reaching 12 inches in trunk diameter in just 15 years. Planted at the same time and just 1/4 mile away, the trees growing in the silty clay soil have grown much slower reaching only 8 inches in diameter. Although the silty clay soil is located within the greater Missouri River flood plain, this land is cut off from minor flooding events by a levy.  In the end, the nut size difference between the two Missouri samples can be attributed to a difference in both available water (the silty clay had less) and tree size. If you remember, tree size has a enormous effect on a pecan tree's ability to capture soil water, impacting both leaf and nut size.

Monday, January 14, 2013

Cold weather and pecans

    We woke up this morning to a world covered with frost and ice. The temperature had plunged down to 10 degrees F (-12 C) and the trees still had a sheen of ice covering their branches from a storm that passed through the area Saturday (photo above). If you look carefully at the photo of native pecan trees above,  you can see where these trees were broken off in the December 2007 ice storm and have now developed a profusion new nut bearing branches.

    The cold temperatures we experienced this morning made me stop and remember the times when we have seen cold injury even on "northern" pecan trees. Cold injury on the cultivars we have under test does not appear until temperatures drop below -15 degrees F (-26 C). A couple of years ago, temperatures fell to -17 F (-27 C) in mid-winter. Shortly after that freeze, I cut twigs from both the Pawnee and Lakota cultivars (photo at right). I used my knife to cut into the stem and reveal the health of the inner bark and the cambium. Lakota was not injured (light green inner bark) while Pawnee suffered cold injury (brown inner bark).  Fortunately, the amount of injury that occurred in Pawnee did not prevent our Pawnee trees from bearing a crop the following summer.
    Back in 1989, temperatures in late December dropped to -27 F (-33 C). At those low temperatures, most trees suffered cold damage. During the fall of 1990, we harvested only 120 Lbs/acre (10% of normal) from our native pecan plots. Of all the cultivars we had under test at that time, Major, Peruque, and Colby were the only trees to produce a decent crop. Most cultivars and many native trees showed some terminal dieback while the more southern cultivars, such as Maramec and Mohawk, had major limb loss or were frozen all the way back to the ground. 

Friday, January 11, 2013

Still harvesting the 2012 native pecan crop

    To many city folks, one of the most surprising parts of pecan farming is the fact that the harvest season often extends well into the winter months. This week, pecan harvesters could be seen buzzing around local native pecan groves still gathering the crop. This is the time of year for "second harvest".  During second harvest, native trees that did not release all their pecans when shook the first time (in Nov.) are shook again. Then the entire grove is harvested again to capture newly fallen nuts and pecans missed during the first pass of the harvesters. At the Pecan Experiment Field, our native plots yielded 1530 lbs/ac during the first harvest with an additional 406 lbs/acre collected during the second harvest. Harvesting the pecan grove twice definitely pays for itself.

Tuesday, January 8, 2013

Pruning a neglected pecan tree

    A lot of pecan growers have read this blog and learned pruning basics. Along the way, I've introduced you to some important concepts for tree training including the 2 foot rule and directive pruning. These methods are designed to be used on young trees and if followed diligently will result in a well balanced, central-leader pecan tree.
    However, all too often, young pecan trees don't receive the necessary intensive training and end up with multiple leaders and numerous narrow angled branch connections. Grafted trees are especially prone to developing poor tree structure because of the tree's natural tendency to produce multiple growing points on terminals. Recently,  a grower in Georgia set me this photo (at right) of a 'Sumner' tree that he inherited when buying a pecan orchard.  His question was simple--"How should I prune this tree to a central leader?".  The simple answer is--"Not all at once". Since trees are three dimensional objects, it is a little difficult to illustrate how this tree should be pruned using two dimensional photographs. However, I'll try my best and hopefully, I'll convey some general pruning guidelines.

    The first step in pruning this tree is to decide which limb should become the central leader. This tree has 4 major limbs all trying to compete for the role of central leader. In the photo at left, the yellow arrow points to the limb I would leave unpruned and the limb I will encourage to become more dominate by pruning the other 3 major limbs. There is one thing to notice about the limb I have chosen to become the central leader. Above the arrow, all the side shoots that radiate off this limb have fairly good branch angles. That bodes well for the future strength of this tree.
    This tree is just starting into its nut production years so I don't want to cut more than one third of the canopy out of the tree in a single year. I'll start by making a heading back cut on each of the other major limbs. This allows the central leader full access to sunshine and will stimulate it to become more dominate. On the other hand, heading back cuts will slow the growth of the other major limbs and force them into more secondary positions. The first heading back cut is shown at right. I'd cut the upward growing portion of the limb back to the point of an outward growing branch. The cut line is marked by a red slash in the photo at right.
    Moving to the other side of the tree, my second cut is shown at left.  Note that I've chosen to prune this limb at the point were it starts to turn upward and strongly compete with the central leader. Again the cut is made to an outward growing shoot and is marked by a red slash.
   My third and final cut is a little difficult to see because its on the back side of the tree.  However, this heading back cut is made just like the other two. The limb is pruned to an outward growing side shoot, removing the portion of the limb that was in direct competition with the central leader (photo at right).  All three heading back cuts are shown by red slashes in this photo. That's plenty of wood to remove in a single year. Ultimately, pruning this tree so it will develop a single strong trunk will be a multi-year project.
     You will find that the limbs that you head back will develop epicormic sprouts near the pruning cut. These sprouts will grow straight upwards trying to take advantage of suddenly available sunlight. You'll need to prune off these sprouts until such time as the central leader grows large enough to start shading them out (1-3 years depending on tree growth rate). Once the central leader starts to dominate, I'd remove the lowest  major limb entirely all the way back to the trunk (photo at left). Over the next, 3-8 years, I'd work my way up the trunk removing the other two narrow-angled branches at 2-3 year intervals.
   Here are three basic principles to remember in pruning young, nut-bearing pecan trees.
  1. never prune more than 1/3 of the canopy out of a tree.
  2. use heading back cuts to slow the growth of side limbs and direct their growth outwards.
  3. remove lower limbs over time. Cut only one major limb every 2-3 years. Your goal should be to develop a tree with 8 to 10 feet of clear trunk.