Pecan weevils emerge right on schedule

   We set up some weevil traps earlier in the week and right on schedule we caught our first adult weevil (photo at right).  The weevil in the photo is a male, and that's a penny at the bottom of the photo to give you an idea of the size of this insect.
   Over the last week we have received plentiful rainfall which translates into ideal soil conditions for an extended adult emergence period. Males weevils emerge first, followed by the females that should start emerging by next week.
    Although adult weevils will feed on nuts and cause nut drop while nuts are still sizing or in the water stage, the females will not be able to lay eggs inside the nut until the kernel starts to fill. With this year's late nut development schedule, I expect to see a lot of weevil induced nut drop during the first half of August.  Since they will be the first to develop kernel tissue, early ripening pecan cultivars will be especially attractive to female weevils looks for egg-laying locations

 

     If you have not installed pecan weevil traps in your orchard, build a few traps and attached them to trees that have had a history of heavy weevil infestations.  The traps will let you know when weevils are emerging and allow you to plan insecticide treatments. Check back on this blog to see when and why we decide to make our first weevil spray for 2013.

Nut development 29 July 2013: Focus on early maturing cultivars

   Between rain showers this morning, I collected some more nut samples to check on the progress of nut development. The first three cultivars I checked were the same three I looked at last week; Osage, Kanza, and Maramec. I had hoped that the 6 inches of rain we've received over the past week would stimulate faster nut development but it looks like things are progressing at their normal pace. We are still at least two weeks behind normal. By the end of July, Osage is usually in full water stage but today, the cotyledon is only half way grown.
  

     After cutting Osage, Kanza, and Maramec, I decided to see how some of our earliest ripening cultivars were progressing this year. Warren 346 is the earliest ripening cultivar we have growing at the research station. Henning, Lucas and Goosepond all originated as seedlings in short season climates. Even these super-early-ripening cultivars have yet to achieve full water stage. Warren 346 and Henning are at 3/4 water, while Lucas and Goosepond have developed to 1/2 water.
    After cutting nuts for a couple of weeks, I've come to the conclusion that when ever weather conditions create a late spring, the entire nut development calender gets pushed back. Let just hope most of our nuts split shuck before this Fall's first hard freeze.

The anatomy of natural limb pruning

   I was walking through the grove checking for scab lesions when I came across a butchered off limb on one of our Giles trees (photo at right). This now-dead limb was the product of the pruning job we were forced to perform in response to massive limb breakage caused by an ice storm in Dec. 2007.  You can see that the limb tried to resprout a few new shoots, but the entire branch stub soon became shaded and died from lack of sunshine.
    While I walked back to the barn to grab a chainsaw, I though-- "why don't I take a look inside this limb to see how pecan trees naturally shed large limbs broken by storms".

    First, lets take a closer look at this branch stub at the point it connects with the trunk (photo at left).  At a point around 2.5 inches out from the trunk, I spotted a line in the bark marked by a slight change in bark color and texture. The yellow arrows point to the top and bottom of this line which actually marks the boundary between living and dead bark tissue.

   Using my chain saw, I pruned off the limb just outside the branch collar revealing nice healthy wood tissue inside (photo at right). Now that this limb has been pruned off, the tree can start callusing over the wound.

    I picked up the pruned-off branch stub to take a closer look. Except for a small portion of the branch that had been closest to the trunk, most of the branch stub was in various stages of wood decay. A nice, white shelf fungus was growing out from cracks in the bark (photo above). The wood was also riddled with insect holes that seemed to be serving as a home for a colony of ants. With all these agents of wood decay and destruction so close to the main trunk, how does the tree prevent additional wood damage? 

   To find out,  I used the chainsaw to dice open the branch stub so I could look at the wood inside. The photo at right shows about 8 inches of the original 30 inch branch stub. However, this is where the action is--where live wood tissue meets decaying wood. The white wood on the left is living tissue that was removed from the tree when I made the pruning cut (described above).
    I mentioned earlier that I could see a difference in bark color and texture between areas of living and dead tissues. Well, that line also shows up in the cross section of the bark. The orange arrow at the top of the photo points to a dark black line in the bark that marks the boundary between living and dead tissues.  And remember those pretty white fungi?  Fungal growth inside the wood leaves a series of fine black lines in unique patterns that wood-workers would recognize as a condition known as "spalting" (see yellow arrow). All the holes in the wood are the result of insect activity; wood borers at first, then a colony of ants. 
    However, the most important thing to see in the wood of this mostly rotten branch stub is the very prominent boundary layer (blue arrow) between healthy white wood and decaying branch. By filling all the pores in the wood with water repelling organic compounds, the tree prevents wood rotting organisms from advancing into the trunk. This plugging of the pores has stained the wood a chestnut brown in a layer about 1/4 inch wide. The outside limit of the boundary zone is marked by a fine black line indicating the limit of fungal activity.  
    If I had let nature take its course, the rotten portion of the branch stub would eventually fall off the tree (years from now). Only then, could the tree start to callus over the wound. However, with proper pruning the callusing process can begin immediately. 

A late scab spray

  

Scab lesions on Giles nuts (24 July 2013)

    We made a fungicide application to our scab-susceptible cultivars today. Two things prompted this fungicide application. First, the 5.5 inches of rain that fell on our grove over the past 5 days combined with seasonably warm temperatures have created the perfect conditions for the spread of pecan scab. Secondly, nut development is much delayed this year and our crop is only now entering the period of rapid fruit expansion; a time when pecans are very susceptible to scab infection (photo above).
    So we mixed some Stratego fungicide in our spray tank and went to work. We did not add an insecticide to the spray tank at this time because it is too early for weevils and we haven't seen any sign of fall webworm or walnut caterpillar this summer.  We'll spray for insects in August when stink bugs and pecan weevil start to invade the orchard.
    This morning I photographed a few of the more scab susceptible cultivars that we have in our collection.  Those photos appear below. Each nut cluster was photographed from the same distance which allows for a direct comparison of the stage of nut expansion (nut size) at this date.  Today, the early-ripening Mullahy cultivar is much larger (further advanced in development) than the late-ripening Dooley cultivar but by harvest, these nuts will be roughly the same size.

Hirschi, 24 July 2013

Dooley, 24 July 2013

Mullahy, 24 July 2013

Pecan crop behind schedule

  

   This morning I cut open some nuts to check on this summer's crop. After receiving more than 5 inches of rain over the past several days, I thought that were would be plenty of soil moisture available to stimulate rapid nut expansion. What I found this morning is that the nut expansion phase is only just getting started (photo above).
   Of the nuts I cut, Osage is the earliest ripening cultivar and is currently in the "large heart" stage of kernel development. Kanza is in the "small heart" stage, while Maramec has yet to enter the period of rapid nut expansion.
  

    For comparison, I dug out the photo I took of these same three cultivars last year (photo at left). On 17 July 2012 Osage was at full water stage, Kanza at 3/4 water, and Maramec at 1/4 water stage. With a record early spring in 2012, last year's pecan crop was roughly 2 1/2 weeks ahead of normal. This year, we had a cool, late spring which delayed tree growth and pushed the pollination season back by nearly two weeks over normal. So it no wonder we are seeing such a huge difference in the timing of nut development. Pecan development is a month later this year as compared to 2012.

The phenology of early ripening in pecan

    Every summer I cut open pecans to check on kernel development. Over the years I've learned a few things about how nuts fill and I have observed the differences among cultivars in nut development rate. In the northern pecan world, only early ripening cultivars are consistently successful nut producers.
  

    During the season, pecans pass through three important stages of nut development. The first stage is rapid fruit expansion.  This stage begins when the developing cotyledon enters the "small heart" stage (photo above) and continues until full water stage.
  

     The next stage of nut development is kernel filling. Starting at the water stage, kernel tissue is deposited inside the seed coat until it has completely filled the inside of the shell (photo at right).
  

The final stage of nut development is shuck dehiscence. During this process, the shuck separates from the shell then finally splits open allowing the nut to fall free from the shuck (photo at left).








    The chart below illustrates the timing of these three stages of nut development for 22 cultivars growing at the Pecan Experiment Field. The cultivars are arranged by ripening date from the early ripening 'Henning' cultivar to the late ripening 'Oconee'.

 

   To help make sense of this information let me focus on the phenology of just three pecan cultivars; Henning, Kanza, and Stuart (chart below). At my location in SE Kansas, these three cultivars represent early, mid-season, and late ripening cultivars. The green portion of the vertical bar represents the period of rapid fruit expansion. The number inside the green bar is the number of days it takes to grow from the small heart stage to the water stage (full nut sizing). In similar fashion, the turquoise portion of the bar represents the kernel filling period while the blue portion records the time required between full kernel fill and shuck split. 

      When comparing these three cultivars, I noticed three time-related differences; the date rapid fruit expansion begins, the length of the fruit sizing period, and the time it takes for shuck dehiscence.  Henning, the earliest ripening of the three cultivars, starts rapid nut growth sooner then moves quickly through each stage of nut development.  In contrast, Stuart nuts don't even start into rapid nut expansion period until 12 days after Henning and then the nut sizing process takes 11 days longer to complete. Once the kernel is filled, Stuart also takes much longer to split shuck--17 days longer than it takes for Henning. 

    As you might expect, nut development start times and rates for Kanza fall midway between Henning and Stuart. At my location, Henning is too early ripening. Despite our best trapping efforts, squirrels seem to harvest much of our Henning crop in August. This is because Henning alone has tasty filled kernels while most other cultivars are still in the water stage. Stuart is too late ripening for our location. Stuart barely splits its shucks before first fall freeze and the kernels are usually fuzzy indicating incomplete kernel fill. Kanza, of course, is just right, ripening right along with our native pecan crop. But, you all know how much I like Kanza.

Pecan seedlings: from simple to compond leaves

  

    As you might recall, I am growing a bunch of pecan seedlings in containers this summer. As my seedlings germinated, the first leaves produced by the new trees had a single blade; very different than the normal compound leaves we see growing on pecan. Now my seedling trees have grown taller they are starting to produce compound leaves (photo at right). The first compound leaf has a large terminal leaflet with only two small leaflets below. Above that, another compound leaf is starting to grow and expand. This leaf will have five leaflets.
    In just a few weeks time, my nursery of container-grown seedling will actually look like a forest of small pecan trees. Before long, every tree should be producing compound leaves.

Poor tree growth and the appearance of stump strouts

        The past couple of summers have been hard on young pecan trees growing in the Midwest. The heat and drought have been brutal. This spring I have seen several young trees produce only a smattering of new leaves on upper branches while sending up vigorous stump sprouts from below the soil surface (photo at right).  The stump sprouts on this tree first developed in 2012 and have continued to grow this year. 

   This year's new shoots are only one-inch in length on the upper portion of the tree (photo at left). The leaves are small and have several missing leaflets. The tree just looks sick!

      At the base of the tree, the bark on the main stem is sloughing off (photo at right). To me, this indicates that the conductive tissues (xylem and phloem) in the stem have been damaged, interrupting the normal flow of water and nutrients.  Its no wonder the top growth on this tree is so anemic.
   The growth of stump sprouts is the tree's way of replacing the damaged portion of the tree with healthy stems that support large, healthy leaves.

    One way to deal with this situation is to coppice the tree (photo at left). It was obvious to me that I was going to lose the original portion of this tree. The growth I found on the upper branches was just too sparse to keep the tree going. On the other hand, one of the stump sprouts had already grown 5 feet tall in two years time.  I simply used my chainsaw to cut down the original trunk and the smaller stump sprouts at ground level.  My tree might have a much smaller top after coppicing but the potential for new growth is much better.
    This tree is a seedling growing in our pecan breeding plots and will remain a seedling in the future. If you need to coppice a grafted tree, plan to re-graft the tree in a year or two.  

    The stump sprout I saved had three equally vigorous shoots growing near the top of the tree. To shape this tree into the central leader form, I tipped back the two side shoots to outward growing buds and left the central shoot free to grow into a strong leader (photos at right). I'll need to watch this tree carefully this summer. There is a lot of root energy pushing the new top growth and that will require plenty of return visits for additional summer pruning.   

Time for new graft training

  

    Now is a good time to start training your successful grafts. Today, I worked on a couple of bark grafts including the tree pictured at right. After removing the deer cage, I cut off all sprouts growing from the trunk below the graft union. I next turned my attention to the shoots growing from the scion. I had left 2 buds on the scion when I grafted this tree and both buds had sprouted and were growing vigorously.
    

    In the photo at left, you can see that both scion shoots are about the same size in diameter.  I could choose to keep either one of these shoots to be my new central leader, but the straighter growth of the shoot on the right gives it a slight edge.  I then cut out the shoot on the left.

    With just one cut, I have established a new central leader for this tree (photo at right). Now all of the tree's energy will be focused into growing the scion's single remaining shoot.

    Like all vigorously growing pecan shoots, the shoot that I kept to become my new central leader was already producing stalked buds (photo at left). To prevent these stalked buds from growing into branches that form serious bark inclusions, I broke off every one of them. Breaking off stalked buds will also help preserve the dominance of the new central leader.

    My next step was to cut off the grafting tape that holds the plastic bag tightly around the scion. The scion on this bark graft should grow rapidly in diameter this summer and I don't want the tape to girdle the scion. After cutting and removing this small piece of tape, I will leave the rest of the graft wrappings in place for now.

    Next, I replaced the bird perch on the graft with a much longer bamboo stalk. I used electrical tape to attach the bamboo to the trunk of the stock, then used flagging tape to tie the new growth to the stake (photo at left). Bark grafts are easily damaged in the wind, so tying the new growth to a stake is a critical part of the graft training process. My final step, was to place the deer cage back over the tree. (No browsing deer is going to ruin this graft!)

Flooding and new grafts: 2013 results

   Back on June 1, I posted a photo of a newly grafted tree surrounded by flood water (reprinted at right). Unfortunately, the water was still rising when I snapped this photo. Later that night, the graft union on this tree became completely submerged. In my previous post, I stated that a new graft will be lost if flood waters cover the union before the tree has a chance to callus in the scion. Today, I returned to this field to see what actually happened.

    At first glance , the photo at left might look like a successful graft, but all the new growth is coming from shoots that originate below the graft union. Hidden amongst the leaves is a very dead scion. This tree was completely submerged during the flood, giving my grafting effort a 0% chance of success.
   

      A hundred feet away, I grafted a tree a little higher on the stem (photo at right). This tree was also located on a little higher ground (we're talking 1-2 inches at most). Although this tree was also surrounded by flood water,  the graft union remained above the high water mark.  By escaping the flood, the graft placed on this tree remained viable and is now growing rapidly.
     I grafted about a dozen trees in this field in 2013. In every case, graft unions that became submerged in the flood failed. On the other hand, I've had great grafting success on trees with graft unions placed above the flood's peak. 
    I'll let the trees with failed grafts grow out for a couple of years, encouraging them to grow tall and straight. With a larger tree, I can graft higher on the stem and hopefully avoid future problems with floods.