Thursday, July 28, 2011

Symptoms of drought

   We haven't had a summer this hot and this dry in SE Kansas since 1980. Talk to some old-timers and they still recall the droughts of the mid-1950's. Before that, it was the dirty '30s and the droughts that created the depression era dust bowls.   
    Pecan trees tolerate heat and dry weather better than many tree species but we are now seeing signs of drought stress especially on young trees. In the photo at left, you will note several dry, brown leaves among healthy, green leaves. This is not the result of some foliar disease but is a perfect example of how pecan trees deal with drought. When the supply of water becomes very limited, pecan trees will conserve water by shedding leaves to reduce the amount of water lost to transpiration. The oldest leaves (at the base of this years new growth) are the first to be shed.
    Watering trees at this point will not "cure" the leaves that have already turned brown but will help trees retain all the green leaves still on the tree.

Wednesday, July 20, 2011

Transplanted trees need water

    It has been 8 weeks since we've had a good rain shower in the Chetopa, KS area. Today I spotted the first casualty of our hot dry weather (photo at right). The tree in the photo was transplanted with a tree spade last winter. You might remember that I photographed the transplanting back in a February post.
   When a tree spade is used to move trees the soil/root ball that moves along with the tree remains disconnected from the surrounding soil. Normal capillary channels that allow water to move upward from deep in the soil profile are severed by the shovels of the tree spade. Once the tree uses up the water held in the soil/root ball, no additional water can move towards the roots. Essentially, during the first few years after transplanting, a spaded tree acts just like a tree growing in a pot. And like container grown trees, you can never let the soil/root ball dry out.
    To ensure transplanted trees survive, I recommend that all vegetation around the spaded trees be killed. I'd use a tractor mounted rototiller to work the soil (shallow cultivation) around each tree making sure the seam between the soil/root ball and the surrounding soil does not split open. And finally, I'd invest in a 2000 gallon water tank and trailer so I could thoroughly water each tree.
   In my experience, it takes at least three years of vigilant care to get spaded trees off to a good start. After several years the soil/root ball becomes reconnected to the surrounding and the transplanted trees starts to grow at a more rapid pace.

Monday, July 18, 2011

Bark inclusion blowout

   Back in May I talked about the problems associated with narrow branch angles and bark inclusions. Sometime after I wrote that post, I was driving by a native pecan grove and came across this major limb broken out under the weight of a heavy crop of leaves.  We did not have a storm to cause this kind of tree damage, but you can plainly see the large bark inclusion at the point of breakage.

   Here is a closer picture of the bark inclusion. Note that the only wood holding the limb in place was along the edges of the branch connection (light tan wood). The bark inclusion (dark brown area) extends deeply down the trunk.
   In native pecan groves you can find trees that are prone to the development of narrow angled branches and bark inclusions. Given a choice during the tree thinning process, I would remove these future problem makers.

Thursday, July 14, 2011

Summer Caterpillars

     Sometimes they seem to appear overnight, stripping the leaves from you pecan trees to satisfy their voracious appetites. Walnut caterpillar and fall webworm are easy to spot at this time of year. The first summer generation of these insects is nearing completion with a second, and larger generation staring in mid to late Augusts.
    Pictured at right are the tell-tale stripped leaves left by the feeding of a colony of walnut caterpillars. Look closely at one of the lower branch terminals and you will see a clump of caste skins left behind by the colony of caterpillars that chewed off all the leaves.
    In an earlier post, you can see a walnut caterpillar egg mass. Once these eggs hatch the caterpillars that emerge stay together in a group, eating together, molting together, and eventually dropping out of the trees together to pupate in the turf. Walnut caterpillar larvae are green when first emerging from the egg (1st instar). After the caterpillars molt, the larvae become maroon in color with log dark hairs. They keep this maroon color during the 2nd, 3rd, and 4th instars. At the 5th and final instar the large become totally black with long white hairs (zoom in on photo at left). These 5th instar larvae do 80% of the defoliation that will occur from this pest. 
     Over the years, we have noticed that walnut caterpillar populations vary greatly. Some years you can hardly find a colony while other year this insect seems to defoliating every tree in the grove. Walnut caterpillar populations are kept in check my a small parasitic wasp. In our area, the colonies we've found are small indicating that the wasp is active and working to suppress an outbreak of caterpillars. However, nut growers in Miami Co., KS and Barton Co. MO have seen much larger colonies indicating that that natural biological controls have broken down in those areas. If you have seen a large number of walnut caterpillar colonies during the 1st generation, be prepared for an even bigger 2nd generation.

   With its dirty white web, the fall webworm, can be spotted a half mile away (photo at right).  These caterpillars appear to stay within the web they create but that web is expanded every night as the larvae devore an ever increasing number of leaves.
     Fall webworm populations flucuate from year to year depending on the survival of pupae over the winter months. Warm, wet winters seem to favor the fungi that attack fall webworm pupae reducing the size of the 1st summer generation. Dry weather provides prefect conditions for insect survival so the second summer generation should prove more troublesome.

Wednesday, July 6, 2011

Training young pecan trees: An Introduction

   I have talked about many aspects of pecan tree training in posts scattered throughout this blog. Now its time to put it all together.
   The primary objective for  pruning a  young pecan tree is to develop a strong trunk. To do that, I think its important to understand how trees grow and how they respond to pruning and the environment. In the past, pecan trees always seemed grow in ways that work against our best pruning efforts to develop a strong central leader. However, if you follow the guidelines set forth in this blog series, you'll learn to work with the tree and direct its growth into building strong tree trunk.
    The training young trees series consists of the following posts:
                1. Tree growth habits
                2. The 2 foot rule
                3. Corrective vs. directive pruning
                4. The problem of stalked buds
                5. When to start training
                6. Summing up
The posts are arranged in order as you scroll  down through the blog. However, you can jump to a specific topic by using the links in the chapter list above.

Training young pecan trees: Tree growth habits

   Most pecan growers have observed that training trees to a central leader would be much easier if the tree would only exhibit stronger apical dominance. The fact is,  pecan trees have strong apical dominance but that dominance is not expressed in a way we expect or desire. In the photo at right, you can see how a pecan tree breaks bud in the spring. Note that there is a strong flush of new growth emerging from the apex of last year's shoot while buds further down the stem are showing only the slightest bit of green. The cluster of new shoots is expressing apical dominance over the buds below. The lower buds are greening up only to allow catkins (male flowers) to emerge. Vegetative growth from these lower buds will be totally suppressed. 
      Four new shoots are growing from the top of the shoot pictured above and if left to grow all season these four shoots will develop into a "crow's foot" branch pattern (photo at left). The development of a "crow's foot" at the top of a young tree destroys the central leader, diverting growth to 2-3 leaders (none of them growing straight up). 
    The way pecan trees break bud in the spring defines the structure of open grown pecan trees. In the photo below, you can recognize how, over the years, the "crow's foot" growth pattern can define the structure of a tree.
    You may be wondering--"how in the world did those native pecan trees grow so straight and tall?"  The answer is sunlight. Under forest conditions, competition is high and light is limited. The tree puts all its energy into growing a single shoot that can out-grow the competition and reach for sunlight.  For open grown pecan trees, multiple shoots grow from the apex to take advantage of the full sun.

     The next post in the training young trees series is The 2 foot rule

Training young pecan trees: The 2 foot rule

   The two foot rule is a simple way to remember how to prune young pecan trees during the growing season. There are three tenets:

  • Keep the top 2 feet of the central leader free of lateral shoots.
  • Limit lateral shoot growth to 2 feet per year.
  • Prune out upward growing shoots on laterals.
 The goal of this pruning system is to develop and maintain a strong central leader tree. Lateral branches are kept in bounds but not removed. It is important to maintain a large leaf area on the tree, maximizing the its ability to capture sunlight. The dense tree canopy also catches more wind, causing greater growth in trunk diameter.
    The before and after photos below demonstrate the 2 foot rule in practice. Notice a well defined central leader and compact laterals after pruning.

      The next post in the training young trees series is Corrective vs. directive pruning.

Training young pecan trees: Corrective vs. Directive pruning

    The traditional time for pruning pecan trees has been during the dormant season. In the photos below, you can see a before and after view of dormant pruning. Dormant pruning is corrective pruning. Notice that almost all pruning cuts were made to correct the problem of "crows" feet.  When pruning during the dormant season, you just have to hope one of the branches in the crow's foot is heading in the right direction. There appears to be a central leader in this tree but its is far from being well defined or dominate.  When this tree breaks bud in the spring, a whole new crop of crows feet will develop.

   In contrast, summer pruning is directive pruning. We use our knowledge of  pecan tree growth patterns to prune the tree during the growing season to direct new growth into desirable directions. Starting shortly after bud break, when new shoots are about 6 inches long, we can define the growth of the central leader with  a single snip of the clippers. The photos below show  the terminal of a young tree before and after summer pruning. A single pruning cut (red line marked A) removes all competing terminal shoots, directing all of the tree's energy into growing a single strong shoot that will grow straight upward and become a dominate central leader.

      Don't forget the two foot rule when pruning the spring flush of new growth, . The photos below show the before and after view of the same terminal shoot pictured above. Notice that I pruned off all lateral shoots within the top 2 feet of the terminal.

    I also make directive pruning cuts the the tree's lateral shoots. During the early spring flush of growth, the terminals of lateral branches will sprout several new shoots. Remove any new shoots that point upward. 
    When new growth on lateral branches has reached 2 feet in length tip prune the shoot to a bud that is pointing downward (photo above,  right). Tip pruning lateral branches helps to change the tree limb's focus from shoot extension to radial wood growth (the limbs get thicker). Tipping also promotes dormant buds on older wood to break (photo above, right), ultimately leading to a foliage dense canopy. 
    The next post in the training young trees series is The problem of stalked buds

Training young pecan trees: The problem of stalked buds

    Early summer pruning and the forcing of rapid central leader growth can promote the development of stalked buds. Stalked buds are primary buds that form on short stems (photo at right). If stalked buds are allowed to grow into lateral shoots they will form a weak branch attachment characterized by a bark inclusion. The best way to explain how stalked buds grow into problem branches is with a series of photos.
    Here is a stalked bud that has started to grow and is now 8 inches in length (photo at right). Notice how a bark inclusion is already starting to form on the upper side of the shoot. Also in the photo is a leaf petiole (below the stalked bud shoot) and a secondary bud (between the stalked bud and petiole).
     Allowed to grow much larger, a stalked bud develops into a branch with a weak branch attachment and deep bark inclusion (photo at right).
    Weakly attached lateral limbs should be avoided when training young pecan trees. Limbs with deep bark inclusions tear easily from the tree, creating a huge scar on the trunk. In addition, when limbs with a deep bark inclusion are pruned off during normal "limbing up" operations, the pruning wound left behind does not callous over well. Without a well defined branch collar, the tree has a hard time growing over the bark inclusion.
     If you prune a pecan tree during the spring to force the growth of a central leader, by June you should see strong growth and the development of stalked buds (photo at left). This central leader has grown over 2 feet in height since I pruned to a single leader 5 weeks earlier and all this new growth is covered with stalked buds.
    Here is a close up of the same central leader. Notice that some of the stalked buds have even started to grow into lateral branches. The good news is that if you continue to practice the 2 foot rule you should end up pruning all of the stalked buds off the central leader. Often times the stalked buds are so green and tender that you can just pull them off by hand without using a pruning shear.
     As the tree continues to grow., you should note that the lateral branches that develop below your 2 foot central leader are actually developing from secondary buds left behind when the stalked buds are removed. Note in the photo at left you can see the pruning wound left behind after removing the stalked primary buds. Below that, secondary buds have broken and developed into well angled lateral shoots.

    The next post in the training young trees series is When to start training

Training young pecan trees: When to start training

    Many pecan growers start to prune young pecan trees too soon after transplanting. I my experience, a recently transplanted pecan tree seems to just sit there, growing only 4-5 inches of new shoot growth in the first year (photo at left). What you don't see is the rapid growth that is taking place under the soil surface. Newly transplanted trees grow roots, regenerating a strong tap root (or tap roots) and developing a network of lateral roots. To support active root growth,  trees need plenty of leaves to capture the sun's energy and create the carbohydrates needed to build root tissue.
     During the root regeneration phase that follows transplanting a young tree, do not prune the top of the tree. Pruning at this point only serves to remove leave area and slow down root growth.  A pecan trees will tell you when they are ready to be trained.  Two to three years after transplanting,  the top of the tree will suddenly explode with new shoot growth (especially with proper weed control and adequate soil nutrition). This is the tree's signal that the root system has become well established and the tree is ready to be trained.
     That brings us to the next 2 foot rule. When a tree grows at least 2 feet of new shoot the previous season it is time to either graft a seedling tree or train a grafted tree. The tree pictured at right is ready for grafting, Several of the shoots grew over 3 feet the previous year and even sprouted some lateral shoots from stalked buds. Note that this tree looks like a training disaster--limbs growing every-which-way and no strong central leader. This is a seedling tree that will be grafting soon after bud break. So we will cut the tree off, right under the 1st whorl of branches and set a bark graft at that point.
    Training young trees starts by applying the 2 foot rule right on the growing graft. In the photo at left, you can see that a vigorously growing seedling tree will push both the scion and stump sprouts to grow rapidly. Find the strongest growth shoot growing from the scion and prune all other out. This shoot will be the new central leader. Prune off all the stump sprouts unless your central leader has already grown 2 feet in height. Following the 2 foot rule, you can leave a lateral shoot on below the graft  to help provide leaf area to support the root system (photo below).
    Use a stake to train you central leader (I use bamboo). The stake also provides a place for birds to perch so they don't land on the tender new growth of the central leader and damage the growing point.
    Training a young tree that grows rapidly is relatively easy using the 2 foot rule. It just requires paying attention to details and a monthly inspection (and pruning when necessary) of your trees from May thru July.

   The last post in the training young trees series is Summing up

Training young pecan trees: Summing up

    The goal of training a young tree is to develop a strong straight trunk. I have developed the 2 foot rule to help you achieve that goal. The results of following the 2 foot rule should be a well balanced tree with a strong central leader (photo at right). To acheive these results you will need to:
  • Maintain rapid tree growth with weed control and soil nutrition
  • Make pruning cuts from May until early August using the 2 foot rule
  • Don't be in a hurry to limb-up the tree. Leaves help create a stronger trunk.
  • Remove lower lateral limbs when they get about 1 inch in diameter