Friday, May 27, 2011

Anatomy of a narrow branch angle

   Whenever I talk about pruning pecan trees, I mention the importance of avoiding narrow angled branches. The photo at right is an example of  pecan branches that have formed a narrow angle. Note the bark crevice where the two branches come together and the ridge of bark that extends down from the narrow angled crotch. After cutting these branches out of a tree with a chain saw, I was able to break these branches apart just like breaking a turkey wishbone.
     In the photo below, you can see why narrow angled branch connections are so weak. First, look at the bark that surrounds the exposed wood. Note that at the top of the branch connection, the bark is grey, the same color as the outside of  the branches. This was the area of the bark crevice we saw in the photo above. Along the sides of the exposed wood, the bark is tan indicating the portion of the bark that was split open when I broke apart the limbs.

    Extending downward from the bark crevice and into the wood is a dark area known as a bark inclusion. Bark develops inside the narrow angled branch connection in response to the opening between the branches (the bark crevice). Once a bark inclusion becomes well established, the only wood fibers that hold these branches together are long grain fibers found on sides of the branch connection.  Long grain fibers split apart easily, just like splitting firewood.
    Some pecan cultivars tend to produce more narrow angled branches that others. Removing stalked buds during young tree training can minimize problems associated with bark inclusions.

Wednesday, May 25, 2011

Pecan Nut Casebearer Trap Catch Data

    The table below represents the capture of pecan nut casebearer moths we have set out around the state of Kansas. The casebearer moth flight begins in southern most counties and works northward over time. Growers should start scouting their orchards for damaged nut clusters 10 days after the moth flight has begun. You should starting seeing larval activity 12 to 16 days after first moth capture. Control measures should begin when you see first significant nut entry (2-3% of nut clusters have larvae feeding on nuts).
    Check this post regularly for data updates including additional locations.  General information on casebearer can be found here.

Tuesday, May 24, 2011

Trapping Pecan Nut Casebearer

    The pecan nut casebearer is a major nut feeding pest. Shortly after the pollination season casebearer moths lay eggs near the tip of young nutlets.  The larvae that hatch from these eggs crawl down to the base of a nut and start feeding. The insect chews its way into the center of the nut, hollowing out the inside. You can identify casebearer feeding by the light strands of webbing the caterpillar uses to fasten nuts to the stem (so the damaged nut doesn't fall off) and by the pile of frass at the base of the nut (photo above).
     Each spring, we monitor the activity of the insect by using pheromone and orchard surveys.This year, I've enlisted the help of several growers around the state of Kansas to follow this year's casebearer moth flight using pheromone traps.

    Pheromone traps are easy to use as long as you can identify the target insect.  In the photo at left, two male casebearer moths have become stuck in a trap. The moths are grey, about 3/8 inch long, and feature a prominent ridge of scales across their wings. You can see other insects caught in the trap and even a fallen catkin, but casebearer moths will be the only insect that have a ridge across their backs.
    The spring 2011 flight has begun in the southern most areas of Kansas as of May 20.

Friday, May 20, 2011

Holes in pecan leaves

    If you walk through a pecan grove at this time of year, you are bound to find some new leaves riddled with irregularly shaped holes (photo at left).  These holes were created by the feeding of sawfly larvae.

    The sawfly is not a fly at all but actually a member of the wasp family. The green larvae of this insect are smalll (follow red arrow) and always feed on the underside of the leaf. Sawfly larvae look like caterpillars but have legs on every body segment (moth larvae have some body segments without legs).
     We monitor sawfly populations every spring checking for outbreak population numbers. In years past, sawfly populations have grown so large as to require a pesticide application. This year, the population numbers have remained relatively low and will not require treatment.

Thursday, May 19, 2011

Pecan nut set

     We are half way through the pecan pollination season. Pecan pollen is still flying and there are still pistillate flowers that need to be pollinated. But at this point I'm seeing a pretty good nut set.
    In the photo at left, the stigmas of each female flower in the cluster has turned black indicating that the flower is no longer receptive to pollen. You can tell these flowers have been pollinated because the little nutlets have grown a little plumper. This enlargement of the ovary is in response to the germination of pollen and the growth of the pollen tube down the style towards the ovary. Fertilization, or the joining of male and female gametes inside the ovule will take place in a few weeks.

   This is also the time of year when you will be able to see weak pistillate flowers or non-pollinated flowers fall from the tree. In the photo at right, the red arrow points to a pistillate flower that dropping from the tree. Note how small the aborted flower is compared to the pollinated flowers still firmly attached.    
     If you are seeing a majority of pistillate flowers dropping off your trees, it is a good indication that the trees in your grove did not store sufficient energy last year to produce robust female flowers. Flooding, lack of nitrogen fertilizer, and premature defoliation can all lead to weak pistillate bloom.

Wednesday, May 18, 2011

Mature pecan tree pruning mistakes

    Every time you mow a pecan grove it seems like there is a limb just low enough to knock your hat off and into the brush hog. After you lose enough hats, it becomes clear that some lower limbs need to be pruned. We rarely prune mature pecan trees but when it comes time to get out the chainsaw, making the proper cuts will prevent future problems.
    The other day I spotted a mature tree that features two of the most common pruning errors. The red arrow points to a branch stub. In this case, a limb was pruned off about 8 inches out from the branch collar. The branch collar appears where the limb connects to the trunk and is the natural location for a tree to grow over a pruning wound. In the photo you can see that the branch stub is rotting away, while the tree has developed an exaggerated branch collar in a attempt to seal over the wound. If this branch had been pruned correctly (at the branch collar), the tree would have sealed the wound by now. However, the rotting branch stub prevents proper wound healing and allows wood rotting fungi to penetrate into the heart of the trunk. Rule #1: don't leave branch stubs when pruning.
   The yellow arrow points to a lower limb that has been pruned back at several points but still extends 10-12 feet from the trunk. This limb is now dead and starting to decay (note missing bark on limb near trunk). Hacking back a lower limb places the entire remaining portion in the shade of upper limbs. Pecan is shade intolerant; so if a limb does not received enough sunlight, the tree aborts the limb. The best course of action is to remove lower limbs completely, pruning the limb all the way back to the trunk and just outside the branch collar. If not pruned off, the limb shown in the photo above will probably end up being shaken off during harvest (just hope it doesn't break something when it falls). Rule #2: prune lower limbs back to the point they are attached to another limb or the trunk.

Tuesday, May 17, 2011

Bark grafting

   When you live in an area were native pecan trees are plentiful, young trees seem to pop up everywhere. This is the case on my farm. I've been mowing around volunteer trees allowing them to grow to a point where I don't need to bend over to graft them (I can graft much faster standing up). I  let the seedling trees grow 5 to 10 feet tall (1.5 to 2 inches in diameter) before using a bark graft to establish my chosen cultivar. There are several variations in bark grafting but I've become comfortable making my version of the modified rind graft.
    All bark grafting methods are similar. The scion is inserted between between the bark and wood on one side of the stock. The key to successful bark grafting is to make certain that cambium on the scion is placed in direct contact with cambium of the stock.

    To start the modified rind graft, cut off at least 1/2 of the stock leaving a stump less that 4 inches in diameter (for faster healing I prefer trees in the 1.5 to 2.5 inch diameter range) (photo at left). 
     Next, inspect the stump and look for the "flat" side of the stem. On the flat side, make a downward incision with your knife cutting trough the bark around 3 inches long.(photo at left)
   Now it is time to carve the scion into a shape that will fit under the bark and maximize cambial contact. I start by making a deep cut, removing about 2/3rds the thickness of the scion, This cut is about 2.5 inches long and features a pronounced shoulder at the top of the cut.(photo above)

   I turn the scion over and make a shallow cut into the wood of the back side of the deep cut. This cut is not made parallel to the deep cut but angled to one side. When finished, I have a thin piece of bark adjacent to the deep cut on one side and a much thicker strip on the other. The cut on the back side of the scion should start just below the shoulder of the deep cut and should give the scion a wedge shape when completed. (photo above)

     Next I make a third cut perpendicular to the deep cut along the thick bark strip edge(photo left). I make this cut  just deep enough to expose the cambium and I make certain to leave a strip of bark between the backside cut and the perpendicular cut. At this point my scion has triangular shape in cross section.  I complete scion preparation by making a chisel point on the end of the bud stick (photo above). This final cut should be made on back side of the scion. 

   Now I'm ready to insert the scion into the stock. I use my grafting knife to gently pull the stock’s bark away from the wood on the left side of the bark slit. Inserting the scion between the bark and the wood of the stock, I tap the scion down into the stock until the shoulder of the deep cut fits snugly against the upper side of the stock.  The deep cut should be facing the wood, while the shallow cut should be covered by the raised bark flap and perpendicular cut should fit snugly against the bark slit. (photo at left)
    I secure the graft union with staples (use a 5/16 staple from a light duty staple gun such as Arrow model JT21). It is important  staple down the bark firmly against the scion and to be sure that all air pockets are removed. (Photo at left)
    Like all the grafting methods I use,  I cover the graft union with aluminum foil and a plastic bag. And finally,  I attach a bird perch stick to the stock with black electrical tape  to prevent the birds from breaking out the scion. (photo at left)
    See related posts on maintaining a bark graft one year after grafting and the anatomy of a successful bark graft. 

Monday, May 16, 2011

Spray drift injury

   Last week a local farmer had several hundred acres of crop land sprayed for weed control in preparation for planting no-till soybeans. A farm services company applied a mixture of Round-up and 2,4-D for a quick knock down of all weeds. Unfortunately, the applicator made a huge error in judgement. The herbicides were applied on a day that had both high winds and high temperatures--perfect conditions to maximize spray drift and 2,4-D vaporization.

   The wind carried the 2,4-D more than a mile from the spray site causing massive damage to native pecan trees. Phenoxy herbicide damage to pecan is easily recognized by the curling of new growth and yellowing of foliage (photo at above). As the season progresses the trees will become either partially or totally defoliated. The nut crop will abort.
   From past experience with 2,4-D damage, the trees that survive will take at least 3 years to recover. We are currently working with the Kansas Department of Agriculture to document this terrible event.

Monday, May 9, 2011

Pollination season

   Pecan pollen is starting to shed and pistillate flowers are in full view. In the photo at right, you can see a cluster of female pecan flowers growing a the tip of a new shoot. Female flowers are not very showy.  You can see the reddish stigmatal surface sitting on top of four leafy bracks. Below the bracks is the ovary. There are four female flowers in this cluster.
    The reddish color and presence of stigmatal fluid indicates this cluster of pistillate flowers is ready to receive wind blown pollen. The stigmas of pecan pistillate flowers can range in color from green to orange to deep red.
   The male flowers or catkins of pecan are also ripening and starting to shed pollen. In the photo at right, you will note that the catkins are actually made up of a long series of sack-like structures held under a leafy bracts. As the catkins mature, the pollen sacks grow larger and start to take on a yellowish color. During periods of low humidity, fully mature pollen sacks burst open releasing millions of pollen grains into the air. The pollen is transferred by wind to the receptive stigmas of pistillate flowers.
    Once all the pollen is shed, catkins turn brown and fall from the tree.

Kill the grass

    The most important cultural practice you can use to increase pecan tree growth rate is to kill all competing vegetation in a 7 foot circle around young trees. Yes, kill the grass. You can use herbicides or a thick blanket of wood chip mulch. Either way, total vegetation control is the only way to ensure fast growth during the early years of a pecan tree's life.
   In the photo at left, a young tree has a herbicide circle around the tree. Not only does vegetation control increase tree growth it also stimulates early nut production.
    Once pecan trees grow to 8 or 9 inches in trunk diameter, they seem to start dominating the ground cover and herbicide circles become less important to tree growth and nut production.

Avoiding t-post rub.

    I often recommend using a steel t-post to both train young trees and to help reduce buck rub. However, using steel fence posts have a down side. Once the tree grows above the top of the post the sharp edges of the post can cut into the bark of your tree creating a huge wound (photo at right). The wound is cut into the tree by the action of the wind moving the tree's trunk back and forth against the post.
    There is an easy fix to prevent t-post rub. Cut the neck off a plastic drink bottle then place the bottle upside down over the post. The rounded, smooth bottomed bottle will guard the tree from the sharp, top edges of the t-post.

Wednesday, May 4, 2011

Arrowhead grafting

     When I go out into the field to graft pecan trees, I bring my tools, supplies, fresh scion wood, and the knowledge of several grafting techniques. The method I use to graft a tree depends on both the size of the tree and the diameter of my scion wood. It an earlier post I talked about grafting pecan trees when the tree is ready . One of the trees on my farm had grown over 2 feet last year, so it was time for this tree to be grafted.

    The tree was about 1 inch in diameter so I  decide to use the arrowhead graft. The key to a successful arrowhead graft is in carving the scion into the correct shape. First whittle the scion down into a thin strap (photo left). This strap should be thinner and narrower towards the bottom of the scion. You should also have a pronounced shoulder at the top of the cut surface.
     Next turn the scion over and carefully shave some of the bark off of each side of the scion. Make sure to cut deep enough to expose a thin strip of white wood alone each edge (photo at left). By exposing the wood, you are ensuring that cambial tissue is revealed. A thin strip of bark should remain down the center of the scion. This graft gets it name from the two cuts you make on the back side of the scion. I looks like you are sharpening the edges of an arrowhead.
   It now time to insert the scion into the stock (photo at left). Cut at least 2/3 of the top off of the stock tree. Make a single vertical incision through the bark of the stock about 3 inches long. Insert the scion under the bark right down the center of the incision. You should see the strip of bark that you left on the back of the scion exposed through the crack in the stock's bark.  Note at this point the bark of the stock is cupped away from the cut surfaces (more importantly, the cambium) of the scion.
   To form the stock's bark closely over the scion, I use a light duty staple gun (Arrow JT21) and 5/16 inch staples. Starting at the bottom, I use the staple gun to press the bark up against the edge of the scion and shoot in a staple. I usually use 6 staples, 3 on a side, inserted vertically to hold the bark firmly against the scion (photo at left). It is a little difficult to see the staples because they are the same color as the bark, but you can plainly see that they have bent the bark inward.
    The success of this grafting method is dependent on how well you can force the stock's bark to conform to the scion.
   To secure the scion even further, I wrap the graft union with grafting tape (1/2 inch wide, 4 mill thick, plastic plant tie ribbon). The tape also helps to hold the stock's bark firmly against the scion (photo at left).
    I complete the grafting process by using the same wraps I use for all pecan grafting methods (photo at left). I prevent sun scald by covering the graft union with aluminum foil. To maintain high humidity around the graft union, I place a plastic sandwich bag over the scion and the stock (you'll need to rip a corner out of the bag). I use grafting tape to seal the plastic bag tightly around the scion then again around the stock just below the graft union.
    Last but not least, I attach a training stick/bird perch to the stock using plastic electrical tape (black tape). This training stick extends about 2 feet above the scion and creates a place for birds to land instead of on top of the scion. Many new grafts have been broken by perching birds when scions are not properly protected.
    Once growth starts on the scion, tie the new growth to the training stick with grafting tape to prevent the wind from breaking out your scion.

Monday, May 2, 2011

Spring pruning defines central leader

    A couple of weeks ago I wrote about pecan tree growth patterns and how it is important to prune during the spring to maintain a strong central leader. Yesterday, I was pruning some of my own trees and I was able to photograph an example of the pruning cuts I make at this time of year. Here is a young tree (pictured at left) that is displaying the typical pecan tree growth pattern I had discussed in my earlier post. Note the cluster of new growth at the top of the tree.
    A closer look at the upper portion of the tree reveals that the strongest shoot growing near the tree's apex sprouted from a bud  about 1.5 inches below the terminal bud (photo at right). This made my pruning decision easy. I pruned at the point marked "A" making an angled cut indicated by the red line. With one clip of the shears, I regained control of the tree's growth pattern and focused all that apical dominance energy onto one shoot.
    To further promote the new central leader, I also removed all lateral branches within 2 feet of the tree's top (photo at left). You can see the white wounds left by pruning off the lateral branches. Also note the prominent secondary buds still present below each cut. As the new central leader grows in height,  these secondary buds will break to form lateral branches with strong branch angles.
    It is truly amazing how a few minutes of spring pruning can make training young pecan trees so much easier. With spring pruning, you are directing the tree's future growth. Without spring pruning, you will be spending a lot more time and money correcting poor growth form with dormant pruning..