Don't let pecan trees get top heavy

   Earlier this year, I showed you how to use directive pruning to prevent a tree from developing a bushy, leaderless top. The photo at right is a great example of what can happen when a bushy, multi-stem top is allowed to grow unchecked.  After the foliage of this tree was soaked by a recent rainstorm, the added weight of water on the foliage was enough to bend the tree down to the ground. Fortunately, the main trunk did not break but this tree needed my immediate attention.
 

  Since the top of the tree was so close to the ground, I took a quick photo of the tree's apex (photo at left). I count five new shoots growing out of the top of last year's wood. With all that new growth at the very top of the tree, it is no wonder the tree became top-heavy during a rain storm.

    Fixing this tree was a two step process. First, I pruned the top of the tree. I selected one shoot to be the central leader then employed the 2-foot rule to prune the rest of the tree. I did all this pruning while the tree was still bent over on the ground (no need for a ladder!). The second step was to install a ten foot tall tree training stake to hold the tree upright. I attached the stake to the base of the trunk using some white electrical tape (white? its just what I had on hand). Next, I lifted the tree up and used additional wraps of tape to hold the tree in place against the wooden stake (photo at right). As this tree increases in diameter over the summer, it should gain enough wood strength to hold itself up without the wooden stake.

Monitoring pecan scab and making the decision to spray

  
     Last week I scouted the pecan grove for pecan scab. For the most part, our trees look pretty clean. I had a hard time finding scab lesions on any part of this year's new growth. However, when I walked over to trees of some extremely scab-susceptible cultivars, new scab lesions were present on some of the foliage (photo above). Dooley, Hirschi, and Maramec were covered with scab last year but this year, with a drier than normal month of June, scab lesions were confined to only certain leaves and on the upper leaflets of those leaves. This kind of uneven distribution of scab lesions on foliage can be explained by the simple fact that the scab fungus prefers to attack rapidly expanding new plant tissue. For a short period during the leaf expansion phase of spring growth, weather conditions became perfect for the release of pecan scab spores. When those spores landed on leaflets that were still expanding, they were able to infect the new tissue and create a fresh scab lesion. 

   When most growers think about pecan scab, a mental picture of blackened pecan shucks and small pecans comes to mind. However, scab can cause major problems with the foliage. Scab lesions can form on the rachis of the leaf and effectively cut off water and nutrient supplies to a leaflet. In the photo at right, The terminal leaflet of one leaf has fallen off due to scab while on the other leaf several leaflet have dried up and dropped off the rachis.
     Under growing conditions in SE Kansas, foliar scab is primarily a problem on severely susceptible pecan cultivars (Dooley, Hirschi, and Maramec).  Scab is so bad on these cultivars, I've begun the process of eliminating these cultivars from our grove.  

   The main reason for scouting for scab last week was to see if the fungicide we applied with our casebearer spray was effective for keeping scab lesions from forming on nuts. The photo at left shows a cluster of Dooley nuts. As of last week, small scab lesions had formed of leaves, leaf rachii, and the pedicle of the nut cluster. The nuts remained free of scab.
   On Monday, June 27th, we received an inch of rain from two separate rain showers (early morning and late afternoon). Our temperatures have remained warm in spite of the rain and the increased humidity has made ideal conditions for the spread of scab.

    Today, the day after the rain showers,  we started up the sprayer first thing in the morning to apply a fungicide to our trees (photo above). Since it looked like we had a short window of opportunity to spray this week (additional showers are forecast for Thursday, June 30th thru Sunday July 3rd), it was very important to get a systemic fungicide on our pecan trees to protect our crop. We applied Quilt Xcel at the rate of 19 oz/acre.

Galls on seedling pecan trees

  

   I was trimming up some young trees when I came across a seedling tree that had leaves sprinkled with light green galls (photo at right). These galls are formed by the plant in response to the feeding of an insect called the pecan leaf phylloxera. I find leaf phylloxera most commonly on juvenile pecan trees that have not yet been grafted.

    I photographed a couple of leaf phylloxera galls on the upper side of the leaf blade then flipped the leaflet over so you can see the same galls from the under side (photo at left). On the upper leaf surface the galls a raised, irregular-shaped and smooth. On the lower side of the leaf, the galls are raised with a nipple-like projection in the center of the gall.  

     I cut open one of the galls, then photographed both halves (photo at right). The gall was filled with aphid-like insects. I found both winged adults, and wingless nymphs inside the gall. These small insects feed on pecan plant tissues that make up wall of the gall.

  Eventually the gall splits open on the underside of the leaf allowing winged adults to leave the gall (photo at left). After winged adults mate,  female phylloxerans will find a secluded spot in the rough bark of the tree to over winter.
   I usually don't bother trying to control these insects on juvenile pecan trees. Once I graft the tree, the problem seems to disappear. 

First generation fall webworm hatching

   Today, I spotted a newly hatched colony of fall webworm larvae on a young tree (photo at right). The larvae are so small at this time that are unable to chew up the entire leaflet. Instead, these newly-hatched larvae simply scoured the surface of the leaf turning it light brown in color.
    The larvae have already constructed their dirty-white web to protect the colony from predators and parasites. In the photo, you can see that the web currently covers just two leaves. I controlled this colony by simply cutting off the two leaves, removing the entire colony from the tree, and squashing the insects under foot.
    At this point in the growing season I have not noticed many fall webworm colonies. The colonies I have seen are generally located on trees that did not receive an insecticide treatment for pecan nut casebearer 10 days ago. 

Training new pecan grafts

     I set on a lot of bark grafts this year and the scions are growing like mad (photo at right). So far this year, I've already made one pass through the orchard to prune off trunk sprouts in and effort to force new growth on the scions. Now with plenty of new shoot growth, its time to select my new central leader and prune the scion down to one shoot.

   Two buds have grown from the scion, both creating strong shoots (photo at left). To develop a tree with a single central leader, I'll need to prune off one of these two shoots. Some growers like to leave multiple scion shoots on the tree all summer long. Then, late next winter, they will prune the scion down to one shoot and harvest the extra shoots for scionwood. I like to make the choice for a new central leader as soon as possible. Pruning down to one shoot in mid-June gives me the entire summer to grow a strong and dominate central leader.

    With a single cut, I made my selection for a central leader (photo at right).  When choosing which shoot to save, I choose to keep the strongest growing shoot.  About 80% of the time, the strongest shoot will arise from the lowest bud on the scion.

    Its amazing to see how much a scion can grow in diameter in just a few short weeks. After trimming the scion down to one shoot, I noticed how much strain the green grafting tape tied around the scion was under. To relieve the girdling pressure of the tape, I used my knife to cut off the tape, while leaving the rest of the graft wraps in place (photo at left).
   

    When making a bark graft, I often leave a nurse limb on the tree under the graft to help provide photosynthetic energy to the root system. But when leaving a nurse limb on the tree, I also make sure that upright sprouts don't develop along that limb that could compete with the graft. In the photo at right, I've used red arrows to point out several upright sprouts that have developed on my nurse limb. Once these shoots are removed, the graft will continue to grow without any direct competition.

   The new scion shoot on this graft is growing so rapidly that it already developed stalked buds (photo at left). I used my fingers to grab these elongated buds and pulled them off the tree.  Not surprisingly, I found stalked buds at every node on the new shoot, from the very base of the shoot to the apex. I removed them all.

     On another graft, I found the new scion shoot had terminated with a flower cluster (photo at right). In this case, I pinched off the flower cluster and left the adjacent stalked bud in place (red arrow). This elongated apical bud will become the primary growing point for the scion's central leader. The stalked bud I left in place will quickly resume extension growth originally stalled by the formation of pistillate flowers.

Spraying for pecan nut casebearer

    We began spraying for pecan nut casebearer this morning (photo at right). After discovering 1% cluster damage yesterday and checking the weather forecast for the next week, I decided we better get started.
    Temperatures for today (June 9) thru Sunday ( June 12) are predicted to reach the low 90's each afternoon. Insect development is stimulated by warm temperatures so this year's casebearer infestation should build quickly. In addition, rain is forecast for early next week so I added a fungicide to this spray to provide protection against infection by pecan scab.
    For casebearer control, I decided to use up some of the insecticides we had on hand. Part of the orchard will be sprayed with Eraser (Chloropyrifos) and part with Warrior II (lambda-Cyhalothrin). For a fungicide, we applied Quilt which has two active ingredients: propiconazole and azoxystrobin. We also added a non-ionic surfactant to the spray tank.
   We like to get started spraying as early in the morning as possible. At this time of day, the winds are calm and the humidity is high. Both of these factors contribute getting better coverage of the leaves throughout the entire tree canopy. You can see in the photo above that early morning spraying creates a mist that swirls through the canopy covering both upper and lower portions of the leaves. 

Summer pruning: Techniques up close

   I was working with my young pecan trees and was making some directive pruning cuts when I stopped to photograph a couple of the techniques I use in training trees.

   I always start at the top  of the tree to make sure the tree is still growing a single central leader. By the first of June, this young tree (2nd summer after grafting) had already added over three feet of new growth to the leader but I spotted trouble already. Look carefully at the photo at right and you'll see a stalked bud at each node. Allowing these stalked buds to grow would be a guaranteed way of losing the central leader in a thicket of narrow angled branches. 

   The easiest time to remove stalked buds is right after they form on soft and green shoots. To remove the stalked bud, I just grab the bud with my fingers, pull the bud to one side of the stem, and snap off the bud (photos above). Wait a couple of more weeks to perform summer pruning and you will need a pair of clippers to remove fully formed and hardened stalked buds.

     After addressing the central leader, I move down to the lateral branches. Following the 2 foot rule, I headed back all the lateral branches that had already exceeded 2 feet of new growth. When making the heading back cuts, I always prune to an outward growing bud (photos above). In this case, I was also careful to remove the stalked bud when I made the cut. Heading back existing lateral branches will help keep the tree more compact and will promote the growth of new lateral branches along blind portions of the central leader (areas well below the top of the tree that lack lateral branches).

Trimming up the "pasture" pecan graft

   A few weeks, back I showed how I converted a multi-stemmed "pasture" pecan tree into a single-stemmed grafted tree. Yesterday, I came back to this tree and found that the scion had budded out (green buds) but the graft-union was surrounded by vigorously growing shoots growing from the rootstock (reddish colored leaves) (photo at right). Like most bark grafts, the trunk below the scion developed numerous trunk sprouts. In addition, all the stems I previously pruned off at the ground level had begun to resprout, creating a forest of new shoots adjacent to the stem I had selected for grafting. All of these red-colored shoots will need to be pruned off in order to force the growth of the scion.

   Once the rootstock sucker growth was removed I was left with a single trunk and a budding scion (photo at left). However, I'm sure that I'll need to visit this tree often because the large root system under this "pasture" pecan tree will continue to push up new shoots from just below the soil surface.
   I call this tree a "pasture" pecan tree because this tree had been mowed down year after year during hay harvest. Even though the top of the tree was removed annually, the root system continued to grow in size. Once all haying stopped, the tree burst forth with multiple stems and rapid growth.
  Because this tree has the potential to send up numerous root sprouts, I'll need to be extra careful in using herbicides to control weeds around this tree. Systemic herbicides like Roundup, Liberty, and Remedy could easily enter the tree via hardly-visible new root sprouts and cause tree damage or even tree death.
    However, the benefits of weed control around young pecan trees is well known. Grasses can be controlled safely with a grass specific post-emergent herbicide like Select. To suppress broad leaf weeds and any new rootsuckers,  I plan to use the non-systemic, burned-down herbicide, Gramoxone.  Since Gramoxone works by desiccating live tissue, I will need to be careful not to get this herbicide on the trunk of my tree.
    Eventually, the scion will grow to dominate and will start to inhibit the growth of additional root sprouts. Once that happens, tree maintenance and weed control will be much easier.
 

Pecan crop load and pistillate flower strength

   Yesterday, I spent some time scouting the orchard to get a feel for the 2016 pecan crop. All of the pistillate flowers have been pollinated and I was encouraged when I found a cluster of five nuts on a Kanza tree (photo at right)

    However, most pecan nut clusters have 3 to 4 nuts at this time of year.  Look closely at the nut cluster pictured at left. Above the 4 nuts in this cluster you can see an empty flower stalk (red arrow). This portion of the pistillate flower inflorescence had also produced additional female flowers that have since dropped off the stem. Look closely enough and you will see a nut attachment scar on the stem that indicates the position of the now aborted flower. Now look at the very top of the stem. You should see four small sepals and a rudimentary pistillate flower stigma. This  is an example of a small, poorly-formed flower that would never have the strength to become fertilized or grow into a pecan.
   This single photo can help explain how pecan trees create flower clusters and why some flower clusters are larger than others. Pistillate flower stalks are formed at the end of the current seasons new grow. The number of flowers produced and the ability of those flowers to remain viable is determined by the energy stored in last year's wood. Given enough plant energy, a current season's terminal will start creating pistillate flowers and continue producing new flowers up the stem until the shoot basically "runs out of gas".  Flowers near the base of the flowering stalk are the strongest and are the most likely to become fertilized and produce a viable pecan. As the tree produces additional flowers, the tree gets to a point where it only has enough energy left to produce small or poorly formed pistillate flowers. These poorly formed flowers drop from the tree during the final stages of the pollination season.
   

    The amount of energy a shoot has available to create female flowers is largely determined by the general health of the tree and by the previous season's crop load. A heavy crop load can drain the tree's energy reserves to a point where a tree finds it difficult to produce viable female flowers or even initiate a pistillate inflorescence during the spring following a heavy crop the previous fall. The photo at right shows a flowering stalk that has dried up and all pistillate flowers have aborted (red arrow). Although this shoot had enough energy to initiate flowing, the size of this flower stalk indicates that the flowers were all small and weak.
    Many might think the lack of nut set on this shoot was due to a lack of pollination. However, pollination has nothing to do with the abortion of the flowers on this terminal. Weak and poorly formed flowers will never produce nuts regardless of the amount of pollen flying through the air.

   This year, I've also seen some trees that never bothered to try to create a pistillate flower clusters. Totally vegetative shoots are easy to spot at this time of year because they are still elongating and setting on new leaves (photo at left).  Trees covered with vegetative shoots this year are setting themselves up for a massive nut crop next year.