Stick-tights: When a pecan kernel doesn't develop inside

    We were shaking some Kanza trees today, when I noticed a few bright green shucks still up in the tree. Most often its just one nut in a cluster of 3 to 4 nuts (photo at right). If you look closely at the still-green nut, you'll note that the shuck hasn't even split open. The fact is, this nut will never split open and will become what we call a stick-tight.

     I pulled some nuts off of our pecan cleaner's inspection table to find out what going on inside the nuts that remain stick-tights. In the photo at left, two stick-tights are shown next to two normal Kanza nuts. I cut each of the nuts in half to reveal what is inside the shell. The normal pecans had nicely filled kernels while the stick-tights had kernels that never fully formed.
     It is the maturing seed inside the shell that triggers normal shuck opening. Without a fulled developed kernel inside, the shuck will never open.
    What causes kernels not to fill out? In this case it is not clear. Stinkbug feeding can cause a similar lack of kernel development but the interior portion on the nut would be jet black in color. Disease is not the cause because the nut appears perfectly healthy. This lack of kernel fill is most likely due to a miscue in tree physiology. For some reason the kernel filling process was switched off  during the water stage of kernel development.

    The appearance of these kind of stick-tights at harvest is not exclusive to the Kanza cultivar. When we cleaned our Pawnee pecans, I found stick-tights  with a similar lack of kernel development (photo at right). Thankfully, the number of stick-tights we harvest is only a small fraction of the total number of nuts we collect each Fall. It just drives me crazy to pull stick-tights off the cleaning table and think--what did I do wrong? The answer is probably, nothing. I guess our pecan trees are just not perfect when it comes to filling out every kernel on the tree.   

Kanza, stick-tights and crop load regulation

  Kanza has become a very popular pecan cultivar because no matter the weather, Kanza always seems to produce a quality kernel (photo at right). Over the past four years, I've been watching our Kanza trees closely and I think I've  discovered one of the ways these trees preserve kernel quality even when faced with stressful weather conditions.  It looks like Kanza trees self thin a portion of their nuts to ensure full kernel filling for the rest of the crop.

    We recently harvested a block of Kanza trees and had dumped a load of nuts into the pecan cleaner. When I looked at the nuts swept up by the harvester, I noticed a large number of stick-tights. The photo at left shows an example of field run Kanza nuts before cleaning. There were plenty of good Kanza nuts mixed in with a few sticks, leaves, and dirt clods. But what stands out are the nuts trapped in blackened shucks.
   It turns out that about 12% of Kanza nuts collected by the harvester this year were stick-tights. Just looking at the photo it seems like the percentage should be higher but a nut stuck in the shuck takes up a lot more space than a nut out of the shuck. 

   I separated out several of the stick-tight pecans, peeled the shuck off, and cracked open the nuts. In every case, I found a brown, paper-thin kernel inside. It looks like each of these stick-tight pecans stopped kernel development at the water stage leaving only the seed coat inside the shell.
   The question becomes--"Why did these nuts stop developing during the water stage?".  During the summer of 2014, we experienced an extended period of dry weather that started during the final stages of nut sizing and continued until late August. In addition, our Kanza trees had set an above-average crop. Most pecan cultivars react to these circumstances by aborting a portion of their crop in what is commonly known as a water stage drop. Nuts dropped in mid-summer often disappear by harvest as they decompose in the ground cover.
   Kanza is different. A Kanza tree stressed by drought and crop load turns off the nut development process during water stage for a portion of the crop but those nuts remain on the tree until harvest. 
   The good news is that Kanza seems to do an excellent job of regulating its crop load to ensure that fully ripe nuts are well filled. The bad news is that cleaning the Kanza crop following a mid summer drought will take a little more time to remove numerous stick-tights. 

Drought induced stick-tights

    After harvesting for a couple of weeks we have finally started to clean some of the 2012 pecan crop. Today, I walked over to the piles of rejected nuts that came out of the cleaning plant and grabbed two handfuls of stick-tights. The first handful came from the pile that was blown out of the cleaner by the air leg (photo at right). As you can see, the cleaner blew out stick-tights that had wafer-like kernels and nuts that fell out of the shuck normally but had shriveled or no kernel. These are the type of pecans we definitely want to keep out of our final product.

    I took a second sample from the the rejects that had been pulled off the inspection table by hand. These were all stick-tights but unfortunately, these nuts contained edible kernel (photo at left). The summer-long drought we experienced in 2012 has caused the shucks of some nuts not to open properly. This type of incomplete ripening seems more prevalent on trees with heavy crop loads. It's a terrible shame to waste these perfectly good kernels but if the shucks stay firmly attached the nut, the nut is  unmarketable.  Fortunately, stick-tights with good kernel inside are far fewer in number than the numerous stick-tights we are seeing being blown out of the cleaner (nuts with little or no kernel).

Incomplete shucksplit on native pecans

    Today we switched from harvesting pecan cultivars to picking some of our natives.  While shaking the trees I noticed about %5 of the trees had nuts with green shucks. I climbed out of the tractor and collected some of the green hulled pecans (photo at right). I noted that some of the nuts had split their shucks normally while others were not split at all.

     Taking my knife, I cut into the shuck of a pecan that had not opened properly and popped off the shuck (photo at left). The pecan inside was fully colored and loose in the shuck but the shuck had not split along the four suture lines. This called for futher investigation.

    I collected 3 pecans that had normal shucksplit and compared them to 3 pecans that I had to cut out of the shuck. I then cracked open each of the nuts to reveal the kernel inside (photo above, right). The 3 pecans on the right had shucks that opened normally. The pecans with shriveled kernels on the left were cut out from closed shucks.
    During a drought, some heavily bearing trees "choose" to fill only a portion of their crop. Those pecans that do not fill their kernels do not shuck-split properly. We saw the same phenomenon when we harvested our "Posey" crop.

Giles ripening effected by crop load

    Thirty years ago, Giles was one of the most popular cultivars to propagate in Kansas. Selected from a native grove outside of Chetopa, Giles seemed like the perfect pecan for our growing under our conditions. But grow any cultivar long enough and you'll discover you still haven't found the perfect pecan cultivar.
    Giles has a tendency to over-produce. This leads to all the typical problems associated with alternate bearing including poor kernel quality during "on" years and next to zero crop during "off" years.  However, this year we've seen a new problem with our Giles trees--incomplete ripening.  A quick survey of Giles nuts still hanging from the tree reveals that some nuts have split shuck normally while others have not opened at all (photo above, right). At this point in the season, the nuts have have failed to split, will never open.
     I peeled out some of the "stick-tight" nuts  and cracked open the shells to see if poor kernel development was the reason for lack of proper ripening (like we saw with Posey). In every case, the kernel in the sticktight nuts were just as well filled out as nuts that ripened properly.  Something else was causing sticktights.

   
    Earlier this summer we recorded the amount of fruiting shoots produced by 20 of our Giles trees. These counts revealed a wide variation in crop load. We had Giles trees with as low as 16% fruiting shoots to as high as 70% fruiting shoots.  To see if crop load influenced the amount of incomplete ripening found on a Giles tree, I decided to climb into the hydraulic lift and make some nut counts.  My results can be seen in the graph above. The heavier the crop load (greater % fruiting shoots) the more incomplete ripening or stick-tights we found in the trees.
    Incomplete ripening due to fruiting stress may occur in other cultivars but it is most pronounced with Giles. The drought we experienced this past summer may have also contributed to making the problem worse in 2012.
 

Early harvest

Shaking 'Posey'

Harvesting 'Posey'

     One of the advantages of having pecan cultivars ripen 18 days earlier than normal is that we were able to start harvest earlier than normal (photo above and at right).  Today, we started on some 'Posey' pecan trees. The nuts shook out well but we noticed some green hulled nuts dropping along with nuts that fell fully free from the husks.
    Because of the high moisture content of the green shucks, we decided to run our harvested nuts immediately through the cleaner to blow out any loose green shucks and to remove nuts with the hull still firmly attached. Green shucks in a sack of pecans can cause terrible mold problems.

"Stick-tights" collected during harvest

    Posey had shuck split way back on September 18th; so why where some nuts not opening more than a month later? I collected some of those green hulled nuts and cut them open to check on nut development.  In every case, I found a paper thin kernel (photo at left). One way pecan cultivars deal with drought is to abort a portion of their crop when the nuts are in the water stage and before the tree makes any carbohydrate investments in kernel deposition. These nuts, with little or no kernel development, end up becoming "stick-tights" and are discarded during the cleaning process. 

Why won't some pecan shucks split open?

    We've been harvesting pecans this week and I've noticed quite a few green nuts still up in the trees. With this mornings low temperature registering 24 degrees F, all those green shucks were frozen and are quickly turning black. But long before last night's freeze, there was a reason those nuts where green and still stuck in the shuck (Photo above shows sticktights vs normal nut).
    In a previous post,  I described how pecan weevils can cause pecan shucks to remain green long after normal nuts have split shuck and started to dry. But the nuts pictured above remained green until last night's freeze and failed to open correctly because the kernel inside failed to develop.

    Here is a photo of a well developed Kanza nut vs. a Kanza sticktight (photo at left). You can plainly see that the sticktight nut developed a seed coat but never filled it with kernel (read about kernel filling here). Since the seed coat is a normal tan color, we can assume that the lack of kernel filling was related to this past summer's drought.  Under drought conditions, pecan trees often abort part of their nut crop to be able to fill the nuts that remain.
     If the seed coat had been dark black inside, stinkbug feeding in early August would have been the cause for the lack of kernel development. In any case, it looks like we will have a lot of sticktights to pick off the cleaning table this fall.