Pecan shell geometry and kernel dorsal grooves

      Have you ever cracked open a pecan and gotten frustrated but the shell's inner packing material trapped in the grooves of the kernel (the dorsal grooves). It seems that some cultivars are more prone to this problem and the reason may be as simple as the shape of the nut's shell. I'm not talking about the length of the nut or how pointed the nut appears. When it comes to narrow dorsal grooves and trapped packing material, the important shape to observe is the shape of the shell in cross section. Not all nuts are perfectly round in diameter. In the photo below, I have arranged the nuts of three cultivars so you can see the how nut diameter can differ if measured 90 degrees from the shell suture (nut on left) or on the suture (nut on right). Below each pair of nuts I've listed the diameter ratio (diameter 90 degrees from suture/ diameter on the suture).  A nut that is practically round in cross-section, like Kanza, has a diameter ratio close to 1. Cultivars that produce "flattened" nuts, like Greenriver, have a diameter > 1.  Cultivars with a diameter ratio < 1, such as Chetopa, often appear narrow when viewed suture side up.
 

   So, what does all this have to do with packing material stuck in the dorsal grooves?  Its all about how kernels are oriented inside the shell. When you look at the shell's suture, underneath is a full kernel half. In other words, the inner wall partition between the kernel halves is oriented 90 degrees from the suture line. Lets look at the kernels of these same three cultivars (photo below).

   Cultivars, such as Chetopa, that have a diameter ratio < 1 typically produce long narrow kernels. The dorsal grooves on these narrow kernels are not only narrow themselves but they tend to flare outward into the kernel. The result of this kernel geometry is frequently trapped packing material.
    In contrast, round nuts or flattened nuts have broad kernels with wide dorsal grooves. These grooves also penetrate straight down into the kernel. The result of this geometry are kernels that fall free of all inner shell packing material.   

How long does it take until pecan trees bear a commercial crop?

    The trees in our double-row intercrop block are starting to produce a lot of nuts (photo above). Earlier this fall we even planted a permanent ground cover in the space formerly dedicated to field crops.  Now, with the leaves off the trees, you can see why we needed to plant a ground cover to facilitate harvest--the trees are loaded with nuts.
    A lot of folks interested in establishing a new pecan orchard wonder how long it will take until the pecan trees start to bear nuts. This double-row orchard provides a good example. The orchard was established with contianer-grown trees. One-year-old 'Colby' seedlings were transplanted into the field during the fall of 2002.  The cultivars Lakota, Faith, and Gardner were grafted onto these rootstock trees during the grafting seasons of 2005-2007. The young trees started to set a few nuts by 2009. By  2012 we needed to use a trunk shaker to harvest our first machine-harvestable crop (ie. a crop big enough to justify the expense of running the equipment). The 2013 crop is even bigger and this year we will start collecting meaningful yield data.
    Here's the bottom line. The trees pictured above were started from seed in the nursery during the Spring of 2002. By the Fall of 2013, eleven years later, the trees have grown large enough to bear their first commercial crop.  

Brown fuzz on pecan kernels

    Patches of a brown fuzzy material loosely adhering to the surface of pecan kernels are a common sight this fall (photo at right).  This is not a disease but simply some of the internal shell packing material that has become stuck to the kernel.
    During the 2011 and 2012 growing seasons, the brown fuzzy patches were caused by a summer droughts. This year the problem was just the opposite. The summer of 2013 was cooler and wetter than normal. In fact, nut development ran two weeks behind normal all season long. By the end of the 2013 season, many pecan cultivars ran out of time and heat to fully pack the inside of the shell with kernel.
    If the expanding kernel does not fully compress all the packing material tightly against the inside of the shell, some of that packing material can adhere to the kernel. Note that the brown fuzzy material is generally concentrated towards the upper end of the kernel half. This is the part of the kernel that fills last during nut development.  It seems that time simply ran out for kernel filling as shorter days and falling temperatures promoted nut ripening and shuck splitting. 

The problem with Witte

    The Witte pecan cultivar has been around for a long time (photo at right). It was discovered in the 1920's by J.H. Witte as a native pecan tree growing in the Mississippi River floodplain just outside of Burlington, Iowa.  This northern pecan cultivar ripens early, about 4 days before Colby. The tree produces a medium sized nut (6.6 g) with 51% kernel. Witte has a protandrous flowering habit and is moderately susceptible to pecan scab. From the outside, Witte looks like a fairly good choice for northern pecan growers. However, crack open the shell and you will discover Witte's fatal flaw--Dark ugly kernels.

     Witte kernels are dark even when harvested fresh off the tree (figure left). A few weeks after harvest the kernel color gets even darker. Witte kernels also have a wrinkled "old man" appearance that contributes to an illusion that the kernels poorly filled out.

    You can really see how dark the kernels of Witte are when you compared them to kernels of Oswego and Kanza (photo at right). When consumers are shopping for pecans they associate light kernel color with freshness. Dark kernels are avoided as being possibly rancid.
    Because Witte produces such unappealing kernels year in and year out, I wouldn't recommend this cultivar to any northern pecan grower.

Harvest 2013

     Its amazing how a hard freeze helps to kick the harvest season into high gear. Our pecans are opening up nicely and are drying out quickly. I've been taste testing nuts for a couple of weeks now and for the most part, the nuts have been rubbery and green tasting. Previously, the kernels had just too high of a moisture content. Today, I ate my first fully dry and great tasting pecan from this year's crop--a Faith pecan (photo at right).

    So far, our harvesting equipment seems to be working without any major problems (photo at left). Today, we moved the harvester into the Kanza block. Yields in this block of trees are once again impressive  judging from the number of full super-sacks that are being pulled out the field. However, I'm seeing indications that tree crowding has reduced nut production in sections of this block. Later this winter, I'll consult my thinning plan for this block of  Kanza trees and sharpen my chainsaw.

Deep freeze ends pecan growing season

    The temperature dropped to 18 F early this morning representing this Fall's first killing freeze. When I arrived at the pecan grove, leaves were dropping from the trees so fast they quickly covered the bed of my truck. Its impossible to capture the sights and sounds of such a quick leaf drop with a still photograph but I hope you can see the leaves raining down in the photo above (click on photo to enlarge).

    Last week I wrote about cultivars differences in preparing for dormancy.  By the time the freeze hit today, the cultivars I photographed with yellow leaves last week had already lost their leaves by this week (ie. Greenriver and Kanza). Stuart, on the other hand, was still holding on to green foliage as of yesterday. By one o'clock today, the ground under our Stuart trees was littered with green leaves knocked off the tree by cold temperatures (photo above, left).

    Looking up into the Stuart tree, I found the green shucks had frozen and taken on a water-soaked brown appearance (photo at right). Starting today, the green shucks of Stuart or any other pecan that still had split green shucks will begin to dry, turn dark brown, and pull away from the nut.  Late ripening cultivars that had not begun the split shuck process by today will remain firmly enclosed within a blackened shuck; a condition commonly called stick-tights.
     Let the harvest begin!

Container grown pecan trees: Fall planting and overwintering potted trees

   For the past three weekends, I've been planting the pecan seedlings I started in containers this past spring. Fall is the perfect time for planting container grown trees (photo at right).  For the most part, the soil has just enough moisture to make digging the planting hole easy but is dry enough to allow you to back fill the planting hole with loose, friable soil. Fall planting also allows the roots of the young tree to begin growing out into the surrounding soil almost immediately, helping to decrease transplant shock.

      The trees I planted this fall averaged about 10 to 12 inches in height with an air-pruned root system only about 4 1/2 inches deep (photo at left).  The depth of the root system makes it very easy to transplant--one shovel full of soil and I've got a hole deep enough for the tree. I like to to plant these trees about an inch deeper than they had grown in the container, allowing the root ball to be fully covered with soil. Planting deep ensures that the soil-less media that still surrounds the root system is not directly exposed to drying winds and the tree doesn't desiccate.

     The photo at right gives you a good look at the type of root system that develops inside the bottomless container. The tap root has been air-pruned forcing the development of  a network of fine lateral roots. Once this tree is planted in the field, the air-pruned taproot will re-sprout often creating two or three new "taproots". Next year, my transplanted seedlings will put on just a few inches of new top growth but more importantly, they will be developing massive root systems designed by nature to ensure tree survival.

     I planted about 150 trees this fall but still had some trees left over. With winter's first blast of arctic air forecast for this week, I took some steps to protect my remaining potted trees from the big chill. Although pecan trunks and branches can stand temperatures down to -26 F, the roots of pecan trees will freeze at about +19 F.  This means I needed to take some steps to protect the roots of my remaining potted trees.
    I moved the trees from the nursery bench into my vegetable garden. The garden has two things that makes in perfect for overwintering trees. First, we have raised beds in the garden and the garden paths are just the perfect width for a flat of trees. With a raised bed on either side of the flat, it looks like the trees are partially buried in the soil (photo above).  The garden is also surrounded by a fence that will keep the trees safe from mid-winter rabbit feeding.
    To prevent root freezing, I used a thick carpet of hay packed around the tree flats to insulate and trap the soil's heat around the trees (photo below). 

Scab at season's end

Giles, 4 Nov. 2013

    This past summer we ran some fungicide trials which included a "no spray" treatment. Not surprisingly, fifteen inches of rain in mid-summer helped pecan scab spread rapidly on susceptible cultivars. The photo at right demonstrates what scab can do to the Giles pecan cultivar. The nut the points downward and the nut that point towards the camera will end up in the reject pile as stick-tights. The nuts with open shucks on the right and left sides of the cluster will be harvestable but are smaller in size and not as well filled. All four nuts in this nut cluster were covered in black scab lesions.

Giles, 4 Nov. 2013

      Compare that to Giles nuts treated with three applications of fungicide over the course of the season (photo at left). We didn't get perfect scab control because you can see some scab lesions on nuts at left, but we controlled the disease enough to prevent a reduction in nut size and quality. All of the nuts pictured still had green shucks that had split shucks. Giles nuts tend to stay fairly "closed" after shuck split. After a hard freeze kills the green shuck, the shucks will open up fully. Unlike the scabby nuts pictured above, all of these nuts (at left) will be marketable.
    Scab control this past year was a little tricky. We ended up applying fungicides much later into the season than we even have in previous growing seasons. I was pretty happy with the scab control we achieved. This past season proved how important it is to stay in touch with nut development stage and to make pesticide applications according to the tree's time line rather than the calender date. 

Northern pecan cultivars and fall foliage color

    Establishing early-ripening cultivars is critical for successful pecan growing along the northern edge of the pecan tree's native range. Over the past couple of months, I've photographed many cultivars adapted to northern pecan culture as they ripened this fall (25 Sept. 2013, 30 Sept. 2013, 9 Oct. 2013, and  21 Oct. 2013).  However, ripening date is not the only characteristic that is important for assessing the adaptability of a cultivar for northern pecan production.  

 

   
    Today, I photographed a Stuart tree growing next to a Greenriver tree. As you can see in the photo above,  the Greenriver tree has developed a nice yellow fall color while the Stuart tree is mostly still green with a touch of fall browning.   Greenriver, like most northern pecan cultivars, starts to shut down earlier in the fall than southern cultivars, such as Stuart.  This earlier entrance into winter dormancy means that Greenriver would be far more prepared to withstand a sudden blast of winter cold than the ill prepared Stuart tree.
   

Kanza, 4 Nov. 2013

Many of today's early-ripening cultivars represent hybrids of cultivars of northern and southern origins. That is why we see cultivars like Pawnee and Osage still holding on to their summer green foliage all the way into early November. Although early ripening, Pawnee and Osage act like their southern ancestors when it comes entrance into fall dormancy. This might explain why we have seen cold injury on Pawnee and Osage in some years. Kanza is also a hybrid of northern and southern ancestry, but look at our Kanza trees today (photo at right). Its no wonder that we have not seen winter injury on Kanza across KS, MO and IL. 

Downy spot on pecan foliage

   Back in early October, I was collecting nuts samples from our breeding plots when I took a few minutes to photograph downy spot, a minor pecan disease not often seen in well tended groves. This disease popped up in the breeding plot for two reasons. First, we don't apply fungicides to the breeding block to enable us to check for scab resistance. And second, 15 inches of rain over 4 weeks in mid-summer provided great conditions for disease spread.
   By the time I photographed downy spot, the disease was in in advanced stages of development. Looking at the underside of a leaflet with the sun streaming from above, it is easy to see the irregular shaped lesions of downy spot. Each lesion appears yellow with dark patches at the margins and within the lesion (photo at right).  

   Viewed from the upper side of the leaf, downy spot appears as faint brown patches on the foliage (photo at left). An extensive downy spot infection causes early defoliation in the fall. Prior to early defoliation, this disease can reduce photosynthesis by up to 40%. 
   Downy spot is caused by the fungus, Mycosphaerella caryigena, which overwinters on fallen leaves from the previous season.

    Downy spot gets its name because the disease first appears on the underside of leaves as a faint light green spot that turns white and "downy" as the fungus begins to sporulate. As the season progresses, downy spot lesions grow upward through the leaf blade until they reach the upper leaf surface. At this point, spore production has ceased and the downy spot lesions appear brown in color, especially on the underside of leaves (photo at right).
    Downy spot is usually controlled when fungicides are applied for the control of pecan scab.