Pawnee needs crop load management

    Pawnee is one of the most popular cultivars grown in our area (photo at right). The popularity of Pawnee is based on two factors; the nuts are big and they ripen early. However, Pawnee is a high maintenance cultivar. Pawnee is susceptible to pecan scab and the crop needs to be regulated to insure well filled nuts at harvest.
     Today, I collected a few Pawnee nuts from trees at the old Pecan Field Station. In previous years, I reduced the crop load of overloaded Pawnee trees by using a trunk shaker. Now that I've retired from the University, the field station has been abandoned and Pawnee was allowed to over-produce in 2018.

    I collected Pawnee nuts from two areas. The first was a mature orchard with nuts hanging from every terminal. Prior to 2018, these mature Pawnee trees received a good summer shake every year they loaded up with nuts. The second spot was in a young orchard, just starting to produce nuts. Like all young pecan trees, these Pawnee trees had not reached the age when over-cropping becomes a problem.  The young tree produced normal-sized Pawnee nuts while the over-loaded trees produced much smaller nuts (photo above). When I held those smaller nuts in my hands I could already tell the kernels inside were going to be shriveled.

    As I suspected, the kernels produced by the over-loaded Pawnee trees were smaller, poorly filled, and even darker in color. The two kernels on the far right in the photo above were so paper thin that they would be inedible.
   Pawnee is a cultivar that requires a high level of care but when treated right can produce beautiful pecans. Growing Pawnee profitably means adopting a good scab control program and shaking off nuts during the years when the trees set an over-abundant crop.     

Harvesting Pawnee pecans

    We've been working our way through harvest picking up nuts in a various research plots. Last week we harvested Pawnee (photo at right) and I was pleased to see that summer shaking really paid off in terms of nut quality this Fall. This year's Pawnee nuts are some of the best we've every raised.
    Pawnee has become a popular cultivar in northern pecan states because it ripens early and it produces large, thin-shelled nuts. With a good scab control program and crop load management, Pawnee can be a reliable income producer.  
     However, we have experienced one problem in growing Pawnee that is rarely if ever mentioned--Pawnee nuts do not fair so well when harvested mechanically.

    The shells of Pawnee nuts are so thin that they often get cracked during harvest operations. I collected a few nuts from the cleaning table to show you what I mean. The majority of Pawnee nuts come through harvest fully intact (first 3 nuts in top row, photo above). Many nuts get cracked but the shell still covers the nut meat (top right nut, above). However, about 5% of the Pawnee nuts that come across the inspection table are cracked open, exposing the nut meat inside (nuts in bottom row, above).  Sell-able pecans must have intact shells to protect nut meats from contamination. When we sort our Pawnee nuts, any nuts with exposed kernel are thrown off the table.
   Although consumers prefer nuts with paper-thin shells, they also demand a clean wholesome product. I have come to the realization that pecan cultivars that produce nuts with greater than 56% kernel will suffer significant nut losses due to mechanical harvest using current equipment.  This observation is something I'll keep in mind when evaluating the nuts produced in our breeding program.

In the eye of the beholder: Kanza and Pawnee

     Kanza and Pawnee are the two most popular pecan cultivars being propagated for northern pecan growers (photo at right).  The decision growers make to graft one or both of these cultivars is largely based on the expectation that the nuts they produce will command top dollar in the marketplace. However, the way growers look at pecan cultivars may be entirely different than the way consumers judge pecans.
   Consumers are visually oriented. Given the choice between several, in-shell cultivars most consumers will be attracted to the largest nut and immediately ask if the nut is a "paper shell". It doesn't seem to matter if a quality kernel actually resides inside the shell. Given the choice between Kanza and Pawnee, most in-shell buyers will choose Pawnee based solely on its larger size.

   Everything changes when the nuts are cracked (photo at right). Once a consumer can see the kernel, different visual cues come into play. Kernel color makes the greatest impression. In the minds of the consumer, a light, straw-colored kernel is associated with freshness. Dark or mottled kernels are associated with off-flavors even if the kernel is actually top quality.
    Kernel appearance is where Kanza really shines. A bag of cracked Kanza nuts is filled with plump, light-colored kernels. Cracked with a modern pneumatic pecan cracker, Kanza kernels not only look pretty but entire kernel halves are often freed from the shell.
    In comparison, Pawnee kernels vary widely in appearance, even when harvested from a single tree. Some kernels have a nice golden color while others appear mottled (photo above). This causes the consumer to pause and ask if the mottled kernels have something wrong with them. Offering a taste sample may be the only way to convince a consumer that a mottled Pawnee kernel tastes just fine.
   Its unfortunate that taste, that one human sense that should guide consumers,  is rarely used to select pecans within the marketplace. Both Kanza and Pawnee have excellent flavor, although their flavors differ. Kanza kernels taste sweet and oily while Pawnee kernels have a distinctive buttery flavor. Personally, I like the flavor of both nuts and I find it refreshing to switch up a recipe by simply using a different pecan cultivar.  

Shuck split acoss the midwest

   Last week, I visited 6 pecan orchards across 3 states to check on how pecan shuck split varies with location. Below is a map of the orchards I visited all in the space of 3 days.

      By looking at the map you can see that I traveled both east and north from my home base in Chetopa, KS. What the map doesn't show you is how the seasonal climate differs between these pecan orchards. In the Table below I have listed the annual average cooling degree days for each location as well the the average number of frost free days (above 32 F), and the average number of freeze free days above 28 degrees F.
    Cooling degree days are calculated by the National Weather Service (NWS) as a measure of summer heat used to estimate the energy demand needed for refrigeration and cooling. But cooling degree days also can be used to estimate the amount of heat a pecan tree receives during the summer. Pecan is a heat loving crop and even the earliest ripening pecan cultivars require significant summer heat to fill out kernel and ripen (see pecans and climate).
    The freeze free days above 32 degrees is the most common measure of length of growing season and a number most gardeners are familiar with. But, unlike common annual garden plants, the green tissues on a pecan tree do not freeze at 32 degrees. Pecan leaves and shucks freeze at about 26 degrees which makes the freeze free days above 28 degrees (data reported by the NWS) a closer approximation of average length of the pecan growing season.        

    As you might expect, locations farther north had a shorter growing season than more southerly locations. The two most southerly locations (Chetopa and New Madrid) have the most summer heat. However, there seems to be east-west heat gradient among the 4 other locations that all lie approximately on the same northern latitude. Paola, KS is the hottest during the summer while Carlyle, IL  is the coolest.
    At each location, I checked on the development of two of our most popular pecan cultivars -- Pawnee and Kanza. Lets look at the photos, starting with Kanza.

     On Average, Kanza ripens a few days after Pawnee so I was little surprised to find shuck-split Kanza nuts all across the Midwest.  As you look at the photos you'll note that Kanza nuts look pretty much the same anywhere they are grown. The one exception was at New Madrid where the nuts were covered with black sooty mold that developed following a huge aphid outbreak.
    The one orchard I did not find Kanza fully shuck-split was located in a bottom-land orchard near Paola, KS. From the table above, you can see that Paola has the shortest growing season of all the sites I visited but this location gets plenty of summer heat. What's interesting is that just a few miles away and on top of a limestone ridge, Kanza nuts were fully split open.
    Now here's a valuable lesson. Macro-climatic conditions (as measured by the NWS) may be useful for predicting cultivar adaptation on a general level but micro-environmental conditions will determine the exact timing of pecan bud-break and nut shuck-split at any specific location.
    In the Spring and Fall, cold air flows like water down hill and accumulates in the valleys and low areas. This natural downhill movement of cold air is the reason we have areas in the landscape called "frost pockets".
    The cumulative impact of cold air movement into the bottom-land site near Paola means that things warm up later in the spring and they cool off sooner in the Fall than the nearby upland site. As a consequence, a location where cold air settles has a slightly shorter the length of growing season and a reduced number of cooling degree days. This movement of cold air also explains why the upland Kanza nuts were ripe last week while the bottomland Kanza nut were still a few days away from splitting shuck.

     Now let's look at the Pawnee photos (at left and below). Unlike Kanza, I found a wide range of ripening stages among Pawnee nuts across the Midwest.  At the warmest and most southerly locations, Pawnee was split wide open and had been split for quite some time. When I drove northwards into Illinois I found Pawnee was just starting to split shuck. This was exactly the kind of observation I was expecting to make on the trip.
   Locations with a shorter and cooler climate should ripen pecans later in the year.

     But then I moved into central Missouri and onto eastern Kansas. At these locations, I found that micro-environmental conditions impacted Pawnee nut ripening. The Columbia orchard is in an upland position while the New Franklin site is located in the Missouri river flood plain. The Pawnee nuts I saw in Columbia were similar in ripening stage to the Pawnee I saw in Illinois. But just down the road from Columbia at the Horticulture and Agroforestry  Research Center (HARC) near New Franklin, Pawnee was still tight in the shuck.
    In this case, Pawnee nut development at New Franklin was delayed in comparison to Columbia by two factors--position in the landscape and soil type. The HARC orchard lays at the foot of the river hills in the Missouri river flood plain--a perfect spot for cold air to settle. Pawnee trees at this location are also growing in a heavy clay soil. This type of "gumbo" soil warms so slowly in the Spring that bud-break can be delayed pushing back the entire nut development process.  
    When I arrived back in Kansas, I found that stage of Pawnee ripening mimicked the observations I made for Kanza at the same two orchards. Pawnee growing at the upland site in Kansas was split much like Columbia, MO and Carlyle, IL. At the bottom-land site in Paola the shucks were still tight just like the nuts I saw at HARC.
    In comparing Pawnee and Kanza across all locations this year, the ripening dates for these two cultivars were nearly similar at the four most northerly locations. In Chetopa and New Madrid, Pawnee ripened significantly earlier than Kanza. But every season is a little bit different. If I were to repeat this trip next Fall, I would probably find slightly different patterns of pecan ripening.

Cold injury on Pawnee: Temperature and fruiting stress

Pawnee

   Pawnee is a large, early-ripening pecan cultivar grown by many northern pecan producers (photo at right). In previous years we have noted cold injury on Pawnee when winter temperatures drop below -10 F. So I thought it would be interesting to see how Pawnee fared following a colder than normal winter in the Mid-West. Recently, I asked some friends to provide me with some Pawnee shoots cut from their orchards growing near Columbia, MO. The lowest temperature they recorded at their location was -12 F. For comparison, I cut some shoots from our trees growing near Chetopa, KS where we recorded a winter low of -3 F.  
    In looking for cold injury, I selected both shoots that produced pecans last fall (i.e. fruiting shoots) and shoots that produced only leaves in 2013 (i.e. vegetative shoots). Using my knife, I peeled back an area of bark on each shoot to check for internal browning in the bark and cambium (indications of cold injury).

   The photo at left shows a vegetative shoot I cut from a Pawnee tree growing at the Pecan Field (KS). Inside the oval is a close-up of the tissues inside this twig. Note that everything inside the bark looks green and healthy. No cold damage here. A temperature of -3 F was not cold enough to cause injury to this Pawnee stem.

    Now let's look at a fruiting shoot cut from the same tree (photo at right). Again, a close-up of internal bark tissues is shown inside the oval. Note the internal browning of both the bark and the cambium. In this case, the stress of producing pecans caused this shoot to suffer cold injury at -3 F.

    In Columbia MO the winter low was -12 F. In the photo at right, I've placed two Pawnee shoots collected from an orchard just outside of Columbia. A vegetative shoot is on the left and a fruiting shoot on the right. A close-up of the internal bark for these two shoots is shown within the oval (in same left to right order).
    At -12 F both Pawnee shoots showed signs of internal browning. The vegetative shoot had only very slight discoloration while the browning observed within the fruiting shoot was intense.
    From this year's observations and observations we've made following previous winters, it also looks like Pawnee usually develops cold injury problems when temperatures drop below -10 F. In addition, it is clear that the stress of nut production can reduce the cold hardiness of Pawnee shoots helping to intensify alternate bearing .

Gardner, Faith, and Pawnee

   The cultivar trial we established near New Madrid, MO yielded nuts to allow a direct comparison between three very similar-looking pecan cultivars; Gardner, Faith, and Pawnee. Besides similarities in nut shape, all three cultivars ripen early and are susceptible to pecan scab.
    Pawnee was developed by the USDA and resulted from a cross of Mohawk and Starking Hardy Giant. Gardner originated as a roadside seedling tree discovered in the small village of Gardner, KS. Faith is an open-pollinated Mohawk seedling originally planted by Verna Davis in Arkansas City, KS.
    The evaluation of nuts samples collected in 2012 from the New Madrid point to some differences between these very similar cultivars.

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Cultivar      Nut Wt.  % kernel
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Pawnee        8.14g       55.81
Gardner        6.87g       57.74
Faith             7.64g       55.01  
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   Of these three cultivars, Pawnee and Faith are most alike. However, Faith has constantly produced a smaller nut than Pawnee and Faith nuts may ripen a day or two later than Pawnee. Gardner produces the smallest nut of the three cultivars but Gardner produces significantly more percent kernel. Gardner kernels also seem brighter than Pawnee or Faith, making for a more attractive nut meat.
   We will be looking deeper into differences between these three cultivars in the future. Hopefully, we'll find key cultivar characteristics that can be used to more easily distinguish between these three very-similar-looking pecans. 

Pawnee kernels defects following 2012 drought

    Last fall, many of our Pawnee kernels developed dark blotchy spots in response to last summer's heat and drought. In looking over Pawnee samples provided by growers for this year's nut evaluation, I found a wide range in kernel appearance. The photo above illustrates these kernel defects. There are two kernel halves from each of four Pawnee samples.
    The two kernels in the lower left portion of the photo came from a well irrigated tree that I would consider "normal" in appearance. The kernels in the upper left position suffered the greatest drought induced color changes. These kernels are dark, covered in black blotches and have adhering kernel fuzz. These tree were not irrigated last summer.
    The kernels in the lower right position are less-intensely blotchy and slightly darkened. These kernels were produced by trees had a limited supply of water last summer provided by trickle irrigation. This nut sample points out one of the deficiencies of trickle irrigation in pecan orchards. Under severe drought conditions, many trickle systems can't provide enough water to totally eliminate water stress.
    The kernels in the upper right position illustrate a different type of kernel discoloration.  Rather than numerous small black blotches, these kernels have a large, uniformly-dark area centered on the eye of the kernel (the kernel eye is that area where one kernel half is attached to the other).  With this type of discoloration, the dark spot on underside of the kernel often larger that what appears on the upper side.
    Any type of kernel discoloration will reduce the marketability of pecan crop. A return to more normal rainfall patterns will greatly improve the kernel quality of Pawnee in future years.
   

Pawnee kernel defects caused by drought

    I was cracking some Pawnee pecans and noticed that this past summer's drought didn't effect nut fill as much as it created  kernel color defects. In the photo at right the upper two kernel halves are plump and exhibit normal kernel color for Pawnee. The lower two kernel halves have dark blotches and prominent veins. Look carefully at the lower two kernels and you will see that they are also not as plump as the upper kernels. The area between the dorsal groves looks shrunken and the meats are not fully expanded all the way to the tip of the kernel.
     You can find both types of kernels produced by the same tree. Without enough available water this past summer,  the tree was unable to completely fill out the kernels of all nuts produced. 
    I've tasted both normal and darkened kernels and found little difference in flavor. However, the dark blotches can be a big "turn-off" to consumers. If  Pawnee had just produced some kernels with less than perfect kernel fill and no color changes, no one would probably notice. Blotchy kernel darkening associated with incomplete nut fill seems to be unique to this year's Pawnee crop.

Pawnee vs. Lakota

    I have been a fan of the Lakota pecan cultivar for a long time now and have often described it as a scab free version of the Pawnee cultivar.  These two pecan cultivars share a lot of traits. Both Pawnee and Lakota are precocious, productive, and fall into alternate bearing if not carefully managed. The nuts of both cultivars are large, thin shelled, and have good oil content.
    There are some major differences between Lakota and Pawnee. Lakota is resistant to pecan scab and ice storm breakage, while Pawnee is susceptible to both.  Pawnee ripens more than 2 weeks earlier than Lakota.
   Looking at Pawnee and Lakota nuts side by side you can see obvious differences in nut shape (photo above). Pawnee nuts are a little bit flattened while Lakota nuts are nearly round in cross section. Both nuts have a distinctive yet different apex shape while Lakota tends to have a tapered base.

    I cracked out some nuts to show how each cultivar and their nut shape influences kernels appearance and quality (photo above).  Note that kernel shape mimics the shape of the shell. Pawnee kernels are broad and blocky,  while Lakota are more narrow and tapered.  When it comes to kernel appearance, note that Pawnee has some problems. Pawnee kernels always seem to be covered fine black speckles that can give the kernel a grayish cast.  And in some years (like this year), the kernels can even have large brown blotches. In contrast, Lakota always seems to produce smooth, golden kernels. I guess that's one more reason to like Lakota.

Pawnee suffers winter injury

 

   We cut into some Pawnee twigs yesterday and discovered that the cold snap we experienced back in February (-16 F) has caused some internal browning (photo above). The damage looks like it should not prevent normal bud break and shoot growth but it will be interesting to see if pistillate flower formation is affected by the freeze damage.

   Over the coming weeks we will be evaluating all of our pecan cultivars for cold injury. Then, later in the season, we'll see how the cold injury affect bud break and flowering.    

Pawnee back in action!

The December 2007 ice storm left our Pawnee trees in shambles. Of all the cultivars we have under test at the Pecan Field, Pawnee was one of the most brittle under the weight of the ice (photo at right). Our trees required a massive amount of pruning following the storm and many trees were broken down to the point we had only the trunk and a few stumps of lateral branches left.

This fall is the first year the damaged trees have produced a crop. We knew when we pruned our Pawnee trees that the precocity of this cultivar would help us get back into production fairly quickly. Looks like the crop of Pawnee nuts (photo at right) we harvested today will help us pay some bills at the Pecan Field!

Harvest!

    The pecan harvest season has arrived and we are looking forward to harvesting an above average crop this year. I love this time of year. Cool days and crisp mornings only seem to heighten the excitement of the harvest season.

     I was out talking photos of different pecan cultivars when I spotted a Pawnee nut suspended from the shuck (photo at left). I like this kind of photo because it portraits the action of nuts falling out of the husk when the nuts are fully ripe. But this photo also tells the story of the importance the shuck to nut development. Look carefully at the fibers than are holding this Pawnee nut suspended from the shuck. These fibers are part of the vascular system that lines the inside of the shuck and are attached to the base of the nut. A healthy vascular system is critical for nutrients (minerals and carbohydrates) to be transported from the tree to the developing seed (pecan). The fibers you see in this photo represent only 1/2 of the shuck's vascular system. A networks of vascular bundles also covers the outside of the husk. When visualizing the vascular system of the shuck as a whole, start at the base of the nut where it is attached to the tree. The flow of nutrients from the tree into the nut starts through the outer vascular bundles towards the tip of the nut. Once the nutrients arrive at the tip of the nut they travel through the inner vascular bundles to the base of the shell. All the water, minerals, and carbohydrates needed to build pecan kernel enter the nut through vascular connections at the base on the shell.  So it is easy to see that any pest that damages the husk of the nut will reduce kernel fill.