Friday, September 28, 2012

Wood grain pattern at the graft union

    Back in 2007 we had an ice storm that caused a lot of damage to our pecan grove. In one of our cultivar trials, I found a tree that had suffered massive trunk injury caused by an adjacent tree falling completely over during that storm. Six years later that tree is still trying to heal over the wound (photo at right).
   Interestingly, this tree wound has revealed the wood growth patterns of the tree's graft union. In a previous post, I have shown you what a graft union looks like from the inside (a cross section through the wood). With the bark removed from one side of this tree, we can now see the wood of a graft union from the outside. Note the raised ridge of wood that runs horizontally across the trunk. The color of the exposed and weathered wood is lighter above the graft than below.

  The photo at left is a close up of the graft union. The grain of the wood has a distinctive swirl at the point where the scion meets the stock. I've see this swirl pattern in other grafted trees including apple and peach trees.  Why the swirl? I guess I could make up some fancy explanation, but this time I think it best just to sit back and enjoy looking at one the of nature's miracles. 

Tuesday, September 25, 2012

Mid-season pecan cultivars ripen in late September

   Today's weather was prefect for checking on the development of this year's pecan crop. I found that five more cultivars had split their shucks since last week. Here we are, the last week of September, and I'm seeing cultivars that usually ripen in mid-October fully shuck split today.
    Lakota was shuck split today, one week after Pawnee and Kanza. USDA 63-16-182, a sister of Pawnee, was also shuck split today. Greenriver, Chetopa, and Jayhawk had split their shucks over the past week but Giles, which usually ripens at the same time as Chetopa,  was still not mature. Jayhawk, a Giles seedling, also matured before its parent cultivar.
USDA 63-16-182

Thursday, September 20, 2012

Snap! A young pecan tree breaks in the wind.

     Last week we had a few summer thunderstorms that packed some pretty good winds. Following the storm, I found a young trees snapped in half (photo above). How frustrating!

     My first thought was to see if I could discover why this tree, out of all the trees on the farm, broke in two.  I took a close look at the fractured stump (photo at right). I noted that much of the break was splintered except for two areas of smooth breaks on the southwest side of the tree (yellow arrows). From the appearance of the wood, these smooth breaks were probably present inside the tree even before the tree broke over in the wind. This observation was cause for further investigation.
     I used a chain saw to cut through the trunk of the tree just below the break (photo at left). I found discolored wood on the south by southwest side of the tree. The tree became prone to wind breakage because nearly 1/3 of the tree's supporting wood was dead and starting to rot. What caused this wood decay? The sun.
     This tree was a victim of  overzealous tree pruning. To get lower limbs out of the way of mowing or other tractor operations, too many low limbs were removed from this tree all at one time. This exposed a previously shaded trunk to intense heating by the midday and afternoon summer sun. This heat build up on the south and southwestern portions of the trunk killed the cambium halting all wood and bark growth. The resulting dead tissues attracted wood rotting fungi and the tree was unable to heal over the sun-scalded trunk.
   Now that we've lost the entire top of this young tree and the remaining stump is severely damaged by wood rot, I've decided to cut this tree off at ground level and allow a stump sprout to form a new trunk. In a couple of years, we'll need to re-graft the tree. With all the root energy this tree will have to push new growth, we should be back to nut production in no time.

Wednesday, September 19, 2012

New early ripening cultivars to watch

    Tuesday, I looked at a few of the newer pecan selections we are evaluating to see how they were ripening in comparison to many of our standard pecan cultivars. I found four selections with shucks split.
    USDA 61-1-X resulted from a cross between Barton and Starking Hardy Giant (photo at right). Ken Hunt had evaluated this clone in central Missouri for several years and recommended that it may be better suited a little farther south ( ie. in SE Kansas). This clone has a thin husk that pulls away from the nut at shuck split. This characteristic should mean the nuts will dry on the tree long before we get a killing frost.
    The "City Park" clone came about by planting a Giles seedling in the riverside park along the Neosho River in Chetopa (photo at left). Years ago, I donated several Giles pecan seedlings to the city in an effort to beautify the park. Over the years, I've kept my eyes on these seedlings just to see what happens. One tree produced nuts early and often. Based on the large nut size, the tree we have now called "City Park" looks to be a cross of Giles and Mohawk. We now have this clone grafted at the Experiment Field for advanced testing.
   USDA 75-8-5 is a hybrid of Osage and Creek (photo at right). Thus far, the tree has been very precocious. However, it has been difficult to judge the nut size of this clone because our trees are still quite young and nuts produced on young trees tend to be small. However, as our trees get larger, the nuts of 75-8-5 have gotten larger, ever in a drought year.
  USDA 75-8-9 is a sister to 75-8-5 and has the same parentage (photo at left). Today, 75-8-9 had about 10% of its shucks split indicating that it ripens slightly later than it sibling. 75-8-9 has been a little slower to come into production but heavy nut production on a 4 inch diameter tree is not always a good thing.

Tuesday, September 18, 2012

Pecan cultivars ripening this week

   I love this time of year. The weather has cooled off and the sun feels pleasantly warm when I'm walking through the pecan grove. Today, I spotted even more cultivars with fully split shucks. Of note, Kanza was shuck split today. That is about 17 days earlier than the average for Kanza. I took lots of photos today so enjoy a tour of this week's ripe pecans!




Sunday, September 16, 2012

A powerful lightning strike

    Over the past week, thunderstorms have passed through our area and brought much welcomed rain. However, these storms also contained powerful lightning and one of our native pecan trees received a direct hit (photo at right). The electrical charge that hit this tree exploded the bark off the tree in two long stripes. Bark and wood splinters where thrown over a hundred feet from the trunk.
    Large pecan trees are hit by lightning because the tree's sap acts as a better conductor of electricity than air. As the electrical charge passes through the tree, it heats the  sap so fast it boils with explosive energy. It is this rapidly expanding water vapor that actually explodes wood and bark from the tree.
    A close up look at the damage reveals the relatively narrow path of the electrical charge. In the photo at left, note the dark line near the center of the exposed wood. This the actual path of the lightning strike. All of the rest of the damage to wood and bark was created by the  explosion of water vapor.
   The question now becomes, "will this tree survive?".  Most healthy pecan trees, including this one, will eventually heal over the wound created by a lightning strike. In fact, a quick walk through almost any native pecan grove will reveal several trees with old lightning injuries callused over but still very visible.

Friday, September 14, 2012

Northern pecans: Climatic adapation

     A lot of folks stumble into this blog in their search for information about northern pecans. "Can I grow pecans successfully on my land and what cultivars should I plant?"  These may be among the first questions asked by budding pecan enthusiasts, but before spending a single dime on nursery grown pecan trees, I think it wise to come to an understanding of the northern pecan tree's climatic adaptation.

     Most avid gardeners have become familiar with the Plant Hardiness Zones Map (above).  When people read about "northern" pecans they immediately think northern=cold hardy.  Unfortunately, average mid-winter cold temperature (how the zone map is made) is a very poor predictor for pecan tree adaptation. Pecans grow natively and produce commercial pecan crops in zone 6 in central Missouri but pecan trees will never mature their nuts in zone 6 in Massachusetts even if the tree grows beautifully.

     To understand pecan's adaptation to its environment it is best to start by looking at a map of the natural distribution of pecan in North America (marked in red above). Pecan is a tree that is native to the broad, rich, flood-plains of the Central United States. Note the huge holes in the center of pecan's distribution. These are the Ozark and Ouachita mountian ranges or areas that have narrow flood plains prone to trapping cold air in "frost" pockets. As you look at the edges of the distribution, note the long fingers of naturally occurring pecan trees. These areas coincide with major river flood plains. At my location in SE Kansas, pecans are located in the Neosho River flood plain. Other major rivers in the northern portion of pecan's native range include the Missouri, Mississippi, Illinois, Ohio, and Wabash rivers. In fact, the most northern location of naturally occurring pecan trees is the Mississippi River floodplain between Iowa and Illinois.  But why is the natural distribution of pecan confined to the center of the country?  The answer is summer heat, and lots of it.

   Pecan is a heat loving crop and requires warm summer temperatures (especially warm night temps) to successfully ripen its nuts.  The National Weather Service calculates what they call "annual cooling degree days" as a measure of summer heat and the demand for air conditioning (the formula is ((max temp + min temp)/2) - 65 Fahrenheit). A generalized map of cooling degree days is shown above. For the most part, you will note that the natural distribution of pecan is found in areas with at least 1000 cooling degree days. I frequently use cooling degree days information to help land owners determine if pecans are right for their location but summer heat must be combined with length of growing season to gain a true predictive understanding for pecan adaptation.

    Pecan tree buds and foliage freeze at about 26 degree F.  The freeze free period map above displays the  number of days of temperature above 28 F that can be expected during the growing season. Pecans, even the earliest ripening clones, have all originated in areas with at least a 180 day freeze free period (above 28 F). Note the 180 day line spikes up the Mississippi River bottom between Iowa and Illinois just like the native range of the pecan. In terms of pecan adaptation outside the native range of pecan, I notice a finger 180 day growing season in central Pennsylvania. In the area around Harrisburg, PA  (which also averages 955 cooling degree days) several nut growers have had success growing northern pecan cultivars.
    By combining Cooling Degree Days information with the Freeze Free Period data, I can get a pretty good feel for where northern pecans will perform well.  I always check local data instead of just relying on the over generalized maps shown above. My general rule of thumb has become that even the earliest ripening northern pecans need a minimum of a 180 day frost free period (based on 28 F) and 950 cooling degree days to properly grow and mature a nut crop. 

Tuesday, September 11, 2012

More early ripening pecan cultivars

       Looks like the entire pecan ripening season will be about 2 weeks earlier than normal. This week I found more cultivars with split shucks.
    It looks like Colby split the shuck during the first week of September (photo at right).
    It may be hard to see in this photo but you there is a slight crack in the green hull were the shuck has split along the raised suture of this James pecan (photo at left).
    Norton was fully ripe this week. The shuck is still holding onto the pecan but all four sutures on every nut are split open (photo at right).
    Peruque usually ripens during the last week of September at the Pecan Experiment Field. However, as of September 11 our Peruque crop is full mature (photo at left).
    Like James, the Shepherd pecan cultivar is just starting to split this week (photo at right). Interestingly, both James and Shepherd originated north of the Missouri River in central Missouri.

Tuesday, September 4, 2012

Short season pecans split shuck early in 2012

Warren 346
   The rain we've received over the past 10 days has kicked pecan nut development into high gear. Today, I walked through some of our cultivar trials and was shocked to find split shucks and fully mature pecans. It may be only a handful of short season pecan cultivars but its only September 4th; a date that is early for even the earliest maturing cultivars.
    The earliest ripening pecan we have under trial is Warren 346 (photo at right).  From the looks of the dry shuck, this pecan was probably mature at least a week ago in late August.  Warren 346 originated in Dale Warren's native pecan grove near Chillocothe, MO.

        Mullahy is a seedling pecan discovered in Iowa by Gary Fernald (Photo at right). This early ripening pecan most likely split shuck over the Labor day weekend. For a short season pecan, Mullahy has fairly good nut size.


    Henning is a cultivar that originated near Brunswick, Mo that probably ripened about the same time as Mullahy (photo at right). The nut is small and seems to be a favorite for wildlife predation.

     Goosepond was also found near Brunswick, MO (photo at right). But for an early nut, this pecan has good size. At this point, about 50% of the nuts on the tree have split their shucks.

    Osage has also started to split shuck (photo at right). At this date, about 25% of the Osage nuts have split open. Osage is the earliest ripening pecan cultivar released by the USDA Pecan Breeding Project.