Tuesday, September 1, 2015

How full are pecan kernels today?

    The first day of September was a good day to check on the development of the 2015 pecan crop. I collected nuts from 14 different pecan cultivars ranging from the very early ripening Warren 346 to the late ripening (late for SE Kansas) Mohawk. I cut a nut from each cultivar in half so I could look at kernel development. Remember to click on each photo and you'll get a much larger view of the nuts in cross section.

   The photo above shows five early-ripening cultivars. Warren 346 is fully packed with kernel with all the internal packing material compressed to a orange-brown color. Shepherd and Colby nuts are largely filled with kernel but the light color of the packing material indicates that nut fill is still progressing. The Osage nut has a kernel that still has several air gaps. However the color of the packing material indicates that kernel fill is nearly complete and we might be left with a poorly filled nut meat. Faith is typically an early maturing cultivar however this nut has a long way to go in filling out the inside of the shell.

  This second group of cultivars (photo above) includes nuts that typically ripen during the first 10 days of October. Posey, Yates 68, and Surecrop kernels have filled all the space inside their shells except for a fine line down the middle of each kernel half. Major and Kanza have a lot of kernel filling to go. These two cultivars have developed only a thin layer of kernel. It looks like Major and Kanza may ripen later than normal this year.

     The final group of cultivars represent pecans that typically ripen during the last two weeks of October. Mohawk is still in the water stage with only the slightest evidence of kernel deposition. Mohawk is also the latest ripening cultivar among these four pecans. Greenriver was still mostly water but the nut has developed a visible layer of kernel just inside the seed coat. Both City Park and Lakota have a visible layer of white kernel and a prominent layer of "gel" inside. This gel layer will soon solidify and become solid white kernel. 

    A pecan enters the final stages of nut maturation when the shuck begins to separate from the shell. This process starts at the apex of a nut and works towards the base. Of all the nuts I collected on September 1st, only Warren 346 showed the first signs of shuck separation (photo at right). Over all, nut development this year seems behind schedule. This is probably due to the cooler than normal summer we have experienced in 2015. However, plentiful rainfall during August should guarantee excellent kernel quality at harvest.

Monday, August 31, 2015

Late season aphids

   The leaves of our pecan trees are starting to take on a sticky and shiny appearance (photo at right). That's because foliage is now covered with honeydew, the by-product of aphids feeding on the underside of the pecan leaves. This year, honeydew coverage of the leaves has been minimized by an unusually large amount of summer rainfall washing the leaves clean. Despite the rain, aphids are still at work, creating even more honeydew.
    I've seem some development of black sooty mold on the leaves (photo at left). This black fungus grows on honeydew and does injure the leaves directly. Indirectly, sooty mold harms the foliage by blocking sunlight and reducing photosynthesis.

   Turn over a leaflet and you'll see the insects that are creating all that honeydew. During the peak of an aphid outbreak, you will find all life stages of the black-margined aphid feeding on pecan tree sap. In the photo above, a winged adult can be seen feeding on the leaflet's main mid-rib. Note the black markings along the outer edges of the insect's otherwise clear wings. Its obvious how this insect received the common name--black-margined aphid.
    Also in the photo you can see various sizes of wingless aphids nymphs. If the nymphs can avoid being eaten by lady beetle or lacewing larvae, they will all grow into winged adults. As a nymph grows in size it must shed its old, smaller exoskeleton before growing into a new larger exoskeleton. Cast-off exoskeletons appear in the photo as white to grey bits of fluff.
   Aphid populations can grow rapidly but eventually crash as pecan leaves become less suitable for aphid feeding. Spraying pecan trees for aphid control seems only to create insecticide resistant strains of the aphid. In our orchard, we have chosen to let the aphids run their course and not spray to control the population.      

Tuesday, August 25, 2015

That tree is not a Giles!

   Years ago, we started a scionwood orchard to produce high quality scions for growers to graft onto their seedling pecan trees.  When we established this orchard, we took great care to graft with scions from known trees that were true to cultivar.  But several years ago, I noticed that one of the trees marked "Giles" (tree 17 in row 6) in the scionwood block ripened well ahead of all the adjacent Giles trees. Even though the nuts are roughly the same size and shape, I noted that nuts collected from the tree we are now calling, SWB617, has a different shuck appearance. Giles nuts have prominent wings along shuck sutures. SWB617 does not. (photo above).

     I cut open a Giles and a SWB617 nut yesterday to check on nut development (photo at left). Wow, what a difference. Giles was still in the water stage and SWB617 had packed the inside of its shell with kernel.
    The question is--where did this early ripening tree come from? I looked at the trunk of the tree and it certainly looks like it was grafted near ground level just like all the rest of the Giles trees in the same row. But how could one piece of unknown scionwood get mixed up into a whole bag of Giles wood? Not only that, SWB617 doesn't look like any cultivar we have on the farm. I'm now convinced that the original Giles graft died and the seedling root grew up to take it place. That would make SWB617 a open-pollinated Giles seedling (we used Giles seedlings to start the planting).
   Last year, SWB617 produced a nut that averaged 5.79g and had 56.61% kernel. For comparison, Giles averaged 6.36g and produced 52.66% kernel. SWB617 matured during the last week of September in 2014 and showed little or no scab infection. In 2015, SWB617 has some scab but not as bad the scab found on adjacent Giles trees. In contrast, SWB617 had more powdery mildew on nuts than found on Giles nuts.  Because this tree ripens early, it will definitely be worth watching. I've even grafted a few more trees of this seedling to see how it acts as a grafted tree.
   So in the future, when I mention a tree called SWB617 you will know a little of its background and why I labeled it based on the location of the tree at the research station--Scion Wood Block row 6 tree 17.

Monday, August 24, 2015

Spraying for pecan weevil

   In our little corner on SE Kansas, we've had over 6 inches of rain in a 5 day period. While the rain is welcomed at this time of year to help fill pecan kernel, wet soil conditions have lead slow steady emergence of pecan weevils. So today,  with sunshine, calm winds, and cool temperatures, we applied a second dose of insecticide to keep weevils in check (photo at right).  This time we applied Sevin insecticide making sure our air-blast sprayer covered the entire tree canopy.