Pecan kernel filling: August 2012

     Over the past month I have been showing you the development of pecan kernel inside the nuts of three cultivars: Osage, Kanza, and Maramec. My first post showed all three cultivars in the water stage on August 3rd. Then I showed you how these pecans were filling kernel on August 10th, followed 10 days later with a post on August 20th. Another 10 days have passed and its time to see how things have progressed (photo above). Remember, we finally got some much needed rainfall during the weekend of August 24-25-26 and kernel filling is now much improved. Osage and Kanza are now tightly packed with kernel. The late maturing Maramec nut seems to be still working on the kernel filling process. With the remnants of tropical storm Isaac predicted to graze our area this weekend, the additional rainfall should allow all cultivars to develop full kernels.
     To make it easy to see how pecan kernel developed over the month of August, I've patched together the photos from August 10, 20 and 30 (see below). In every photo, Osage is on the left, Kanza in the center and Maramec on the right. 

   
    Its interesting to note that the 1.7 inches of rain that fell last weekend not only helped pack out the kernel of all nuts but it also caused the shuck of the Kanza and Maramec nuts to thicken significantly. It is likely that the rain came too late in the development of the Osage nut to effect the shuck of this early ripening pecan.

Time for weevil control

  Wide spread rainfall over this past weekend has enabled pecan weevil adults to emerge from the soil in large numbers. Growers from Kansas, Oklahoma, and Missouri have all reported catching lots of weevils in their 'Circle' weevil traps.The time to control this perennial pecan pest is NOW!
     We started spraying our pecan orchard this morning and this year we are using Sevin XLR insecticide. Other isecticides labeled for pecan weevil control include Warrior II, Silencer, Hero and Proaxis.
   The photo shows a female pecan weevil looking for just the right spot to drill through shuck and shell to enable her to lay 5 to 7 eggs inside the pecan. To control pecan weevil, you must prevent female weevils from laying eggs.

Building pecan kernel? Just add water.

    Last Friday I cut open pecans to see how crop load and drought interact to affect kernel filling. If you recall that post, I discovered that trees with heavy crop loads were way behind in terms of kernel fill. Well, a lot has changed in just 72 hours. We received 1.70 inches of rain over a 2 day period (Sat. & Sun.) with every drop soaking into the soil. The result has be an explosion of kernel filling. This morning I collected nuts from the same trees as before and cut them to inspect kernel fill. In the photo above, the 2 nuts on the left side are from a light bearing Giles tree (28% fruiting shoots) while the 2 nuts on the right are from a tree holding a good crop load (60% fruiting shoots). The 2 nuts on the top row were cut on Friday while the 2 nuts below where cut today (Monday).  The amount of kernel packed into nuts from both trees has increased over the weekend. However, the rapid development of kernel in the tree bearing a good crop (60% fruiting shoots) is truly amazing. Unlike last week, there is now only a slight difference in kernel filling due to crop load. 

    Now lets look at pecans cut from Chetopa pecan trees. For this cultivar, I selected a tree with 46% fruiting shoots and compared to a heavily bearing tree (76% fruiting shoots). This past weekend's rain storm promoted rapid kernel development in nuts from both trees. However, the nut from the heavily loaded tree is still struggling to fill out the kernel. Note that kernel near the inner wall partition is not as well developed as the kernel located adjacent to the outer shell. With 76% fruiting shoots, this tree may have too many nuts on the tree to ever get 100% kernel development.
     With more rain forecast this coming weekend, it looks like we should expect good for kernel quality for the 2012 Kansas pecan crop.

Pecan crop load, nut size, and kernel filling

    This summer, we have been looking at the influence of crop load on nut production, especially during this year's drought. Today, I collected a few nut samples in this trial to check on the progress of nuts growing on Giles and Chetopa trees. I selected two trees from each cultivar; each tree with widely differing crop loads.
   The photo at right shows Giles nuts collected from a tree with a light crop (28% fruiting shoots) vs. nuts collected from a tree with a good crop (60% fruiting shoots). Its easy to see that the tree with a smaller crop load had larger pecans.

    This summer our Chetopa trees have a greater overall crop than the Giles trees but you can still see a difference in nut size between the tree with the small crop load (46% fruiting shoots) and a large crop (76% fruiting shoots). Again, fewer nuts on the tree results in larger nut size.
    The simple relationship between crop load and nut size means that pecan trees can partially compensate for yield loses associated with a weaker nut set by growing bigger pecans.

    I also cut into all the nuts I collected to check on kernel development and was somewhat surprised at what I found. Giles kernel development was far more advanced on the light crop load tree as compared to the good crop load tree (photo at right). Could it be that, in this year of short water supply, the tree with the good crop was "waiting" for more water before it could begin to fill the kernel?

    I cut into the Chetopa nuts and found a similar trend although not as striking (photo at right). Kernel development was farther along on a tree with a lighter crop load. To fully understand the kernel filling process check out this post.
   It will be interesting to see if the differences in nut develop present in mid-August will be visible as differences in kernel quality come this November (harvest time). 
   

Squirrels are already eating pecans

    This summer we have been using catch traps to collect anything that falls from the tree in an effort to discover the causes for mid-season nut drop. During this past week, we've collect a large amount of shell fragments (photo at right). These shell fragments are created by squirrels feasting on pecans that have just recently started to fill their kernels.
    If you are seeing a lot of squirrel damage in your pecan grove at this time of year, shooting the varmints is about your only option. We have been running conibear traps all summer long with good success. However, once the new crop enters the dough stage, our success at trapping squirrels goes way down.  It seems that the squirrels prefer the new "green" nuts to the old crop nuts we use to bait the traps.
    It time for a 22 caliber rifle and a steady aim.

Pecan tree spacing and drought stress

    Last winter I wrote about  thinning a block of Kanza trees. If you recall, we thinned only a portion of a Kanza block last winter with additional tree removals planned for this coming winter. In any case, this left the planting with Kanza trees at two different tree spacings. The original planting was made at 30 ft. by 30 ft. (9.1 m x 9.1 m). After we thinned the trees on the diagonal, trees in the thinned portion of the orchard were spaced 42 ft. by 42 ft. (12.9 m x 12.9 m). Well, this summer's drought has got me thinking about tree spacing and its impact on tree water uptake. So this morning, I went out to collect some nut samples.

    In theory, trees spaced wider apart should have more water available to them than trees spaced closer together. With more water available during a drought year (and no irrigation), wider spaced trees should have bigger and better filled pecans.  To test this theory, I collected nuts from two trees of equal trunk diameter but one sample came from a tree in the thinned portion of the orchard while the other came from an unthinned area (photo above). If I stare at the photo long enough, it looks like the nuts from the thinned portion of the grove are slightly larger than the unthinned area.

     Now, lets look at kernel fill (photo at right). Again, the differences between trees is slight with the unthinned kernel having a fraction more air space within the kernel.
     My theory that wider spaced trees will produce larger and better filled nuts during a drought year may be true but the nut samples I collected today only gave us a hint in that direction. Could it be that the full effect of wider tree spacing hasn't kicked in yet? The orchard was only thinned last winter and the root systems of the remaining trees have yet to take full advantage of the greater soil resources now available to them.
    Hopefully, we'll get some rain and all my worries about water and kernel filling will disappear.     

Drought leads to poor kernel filling

    Its been 10 days since we last looked at the kernel development of Osage, Kanza, and Maramec pecans (see previous post). In the photo above, you can see that both Osage and Kanza have well defined kernels. Maramec is just starting the kernel filling process (note thin layer of kernel developed around the still water-filled void). It is also interesting to note how small the this year's Maramec nut is compared to what we usually except from Maramec.  In a normal year, Maramec is one of the largest nuts we can grow in SE Kansas and is often 1.5 times larger in diameter than Kanza.
    At his point, the kernels of all three cultivars show major air voids and a lack of full kernel development. Last year we were seeing the same kind of poor kernel fill and then we received a major rainfall event that help fill out the kernels. The weather man is promising a general, area-wide rain this coming weekend. Lets hope he's right. If we do not receive a significant rain within the next 3 weeks the 2012 drought will be the cause of record poor kernel quality.

How pecan trees seal off pruning wounds

    Earlier this Spring we pruned off some low hanging limbs from our native trees. During this operation, I took the opportunity to dice up some large limbs with a chain saw to investigate how pecan trees seal off pruning wounds.

   After an hour of sanding, details of the tree's wood growth patterns emerged (photo at left).  The first thing to notice is the dark area marked "R". This is an area of wood rot that developed after a limb had been pruned off several years ago. Above the pruning wound the area of wood marked "C" is the callus tissue that formed to seal off the pruning wound. At the point this large limb was removed from the tree, callus had almost completely covered over the pruning wound.
   There are two more interesting things to note in this cross section of pecan wood. The fine brown line marked "B" is a specially hardened layer of wood cells that forms in response to the pruning wound. This boundary layer prevents wood rotting fungi found in the pruning wound from attacking the newer, outside layers of wood growth. The swirly pattern in the wood grain marked "CW" is what wood workers call "crotch wood".  Furniture makers often feature crotch wood on cabinet doors to add extra interest to their work. In terms of tree structure, crotch wood is actually layer upon layer of new branch collar that develops as the tree increases in diameter. Note that the branch collar was small (narrow) when the branch was small (lower portion) and then got increasingly larger (wider) as the branch grew in diameter (upper portion). Once the limb was pruned off, the branch collar turns into callus tissue to cover the wound and the formation of crotch wood stopped.

The fight for water

   We planted soybeans in our double-row intercrop study again this year. And for the first time, I've noticed that our young trees (11 years old) are starting to dominate over the intercrop. In the photo at left, you can see the perfect outline of the pecan tree root system's  area of influence. Soybeans were planted in the area that is now mostly bare soil (note the 7.5 inch planter rows) but the pecan tree out-competed the beans for water during this drought stricken growing season and the germinated soybeans died from a lack of water.

    I walked up the area in the bean field where the pecan tree's roots had their greatest impact and learned one more interesting thing. A huge soil crack has developed at the boundary between the pecan tree's root system and normal sized bean plants. This says to me that pecan roots are so efficient at extracting water from the soil that the soil has shrunk causing a crack in the soil.   
    This interaction between pecan trees and soybeans has got me thinking. Are the trees getting big enough for me to start thinking about seeding the entire field to a harvester-friendly covercrop?  Soybeans are bringing $16 per bushel: Can I pass up the economic opportunity of an intercrop while the trees are still producing less that 200 lbs. pecans/acre? All I know for certain is that the year to make the switch from intercrop to covercrop is coming soon. I just don't know if it will be 2013 or 2014. Most likely, a flood by the Neosho River will probably make that decision for me.

Cultivar differences in kernel development

    I cut some nuts open today to check on kernel development. In the photo above, you can see large differences in kernel development between cultivars. The early ripening Osage nut has already laid down a large portion of its kernel. The mid-season ripening Kanza nut has entered the gel stage and you can see a translucent thickening just inside the seed coat. Maramec, a late ripening cultivar, has still not achieved full water stage. An explanation on how pecans fill their kernel can be found here.

 

    

   While I was cutting nuts, I decided to check on our Mandan trees. Mandan is a recently released USDA pecan cultivar that is reported to ripen early, one week earlier than Pawnee. This is the first year our Mandan trees have borne a sizable crop, so I could afford to sacrifice a nut to check the stage of nut development. I also cut a Pawnee and Lakota for comparison (photo above).

    Based on the nuts I cut, there is no way Mandan will mature earlier than Pawnee, or even Lakota. Pawnee nuts are now in the dough stage while Lakota nuts are just starting to lay down kernel (early gel stage). Mandan was still in the water stage with no sign of kernel deposition.

    I've been wary of Mandan since its release because of questionable kernel quality. Now, I'm concerned that this new cultivar is not as early ripening as advertized.       

  

Time to install deer protection

    Its almost mid-August, which means that buck deer will soon be searching for just the right tree to rub the velvet off their antlers and mark their territory. Bucks seem to prefer to rub trees in the 1-2 inch diameter range making young pecan trees an ideal target for deer damage.
    Preventing buck rub is important for preserving all the work you invested to train the tree into a nice, straight, central leader. Over the last several years, we've been using a hard-plastic-mesh tree guard that is 3 feet tall to protect the trunks of young trees (photo at right). 
    We installed the tree guards this week (August 8th) and will leave the guards on until sometime next spring. I remove these tree guards every year during early spring to make pruning off trunk sprouts much easier.

Controlling stinkbugs

    During the water stage of nut development, pecans seem to become especially attractive to stink bugs and leaf-footed bugs. Stink bug feeding at his time of year causes nut drop. In a couple of weeks when the nuts stage into the gel stage, stink bug feeding will leave a black spot on the surface of the kernel.
    As part of our annual pest management program, I apply an insecticide at water stage to control kernel feeding bugs. Today we applied Warrior II, a synthetic pyrethroid that is formulated to remain active for at least 2 weeks.  This spray will also control any pecan weevils that may have emerged up through the cracks of out drought parched soil.

Drought induced nut drop

   With the deepening drought, we are starting to see some nut damage (photo at right).  The shucks of drought-damaged nuts develop brown patches, especially towards the apex of the nut. Inside the nut, tissues have turned uniformly brown as the nut appears to be cooked by a lack of water and high temperatures. 
    Once a nut becomes damaged by lack of water, there is no cure, the nut will eventually fall from the tree. For those of us without the ability to irrigate our pecan crop, we can only hope significant rainfall is on the way and additional drought damage can be avoided.

Pecans in the water stage

   Spring came early this year and many of our summer fruit crops ripened 2 to 3 weeks early. Not so for pecan. This summer's heat and drought has slowed pecan kernel development to a point where kernel development now is right on schedule. It's early August and nuts are in the water stage (photo at right).
   The water stage of pecan kernel development can be defined as the point in time when the shell and kernel seed coat have become fully sized and the interior of the kernel is filled with liquid endosperm. Cut a nut open at full water stage and your hands will be soaked by the water that comes pouring out.
   In the photo above, Osage and Kanza are in full water stage while Maramec is still expanding it's kernel (its in 3/4 water stage). At this point, you can also see that the shell has become hardened especially near the nut apex and the inner shell packing material between kernel halves is starting to be compacted by the expanding kernel, turning orange in color. 
    Understanding the stages of kernel development is important for understanding how kernel feeding insects damage pecans. If a pecan weevil or stink bug punctures a nut during the water stage (or any time before water stage) that nut will drop off the tree. Once kernel deposition starts (the gel stage) insect damaged nuts will remain on the tree until harvest.