Wednesday, August 24, 2016

Squirrels feeding on pecans already

   All summer long, we have been collecting nuts that drop from native pecan trees in drop cages. In most cases these dropped nuts were damaged by stink bugs, shuckworm, casebearer, or pecan scab. However, today we found evidence that squirrels have begun feeding (photo above). A squirrel seems to be able to sense the stage of kernel development inside a green-husked nut and will crack open nut as soon as it begins depositing kernel tissue. This usually means that the earliest ripening trees in the orchard will suffer the greatest amount of squirrel damage.
   We have been trapping squirrels all summer long and hopefully we have reduced the squirrel population around our pecan grove. However, looks like we have at least one squirrel that needs a good dose of lead poisoning.  

Monday, August 22, 2016

Kernel filling: 22 August 2016

    August is the month when pecan kernels start to fill. This morning I collected some nut samples from several cultivars and cut them in half to reveal the stage of kernel fill. Warren 346 is one of the earliest ripening cultivars we have in our collections and, as you can see in the photo above, this nut is rapidly approaching full kernel fill. The Peruque nut has laid down a layer of kernel tissue all along the inside surface of the seed coat. The Kanza nut still contained ample water but I could see evidence that kernel deposition has started as the seed coat wall appears to be thickening. For a close up look at the kernel filling process, check out this post: Pecan kernel filling.     

    When I cut open nuts from several mid-season ripening pecan cultivars, I found all three cultivars still in the water stage (photo above). However, you can still see differences in the development of the kernel. As the seed coat becomes filled with water, the water accumulates under pressure and presses outwards to expand the region where pecan kernel will form. Note now the kernel space inside the Lakota nut is much larger than the Waccamaw and Greenriver nuts. Lakota has advanced further towards kernel filling than the other two cultivars.

   I've mentioned a clone we've labeled SWB617 in previous posts. We think this tree originated as a  Giles seedling so I thought it would be interesting to compare SWB617 with Giles in terms of nut development (photo above).  The Giles nut was still in the water stage while SWB617 had started to deposit kernel inside the nut. However, I spotted a potential kernel filling problem inside the SWB617 nut. Notice how thick the layer of kernel has formed on the dorsal side of each kernel half. Compare that to the thin layer that has developed next to the inner wall partition (blue arrow).  
   Uneven kernel deposition is a sign that the tree is under stress and is having difficulty pumping enough energy into the seed. Two common stresses that cause poor kernel fill are lack of available soil moisture and excessive crop load. Water seems to be the culprit in this case. However, all is not lost. A good soaking rain this weekend could relieve the water stress and this nut would still go ahead and fully fill out its kernel.     

Friday, August 19, 2016

Nut Development: Shellbark hickory vs. Pecan

  Over the past several weeks, I've been recording the development of several pecan cultivars. Hopefully, you have been able to see differences in the rate of kernel development between early ripening cultivars and later ripening cultivars.
    Today, I want to highlight the differences in nut development between two distant cousins in the hickory family--Shellbark hickory and pecan. The shellbark hickory produces a huge fruit that appears to be at least 3 times larger than a pecan fruit (photo above right). To check on the development of the nuts inside these fruits, I cut each fruit in half.

     The pecan shell had only just started to harden up and I could slice through the entire fruit with a pocket knife. In contrast, I had to use a band-saw to open up the hickory. In the photo at left, the huge difference in stage of kernel development between species is very clear. The shellbark hickory is fully packed with kernel while the pecan is still in the water stage.
    The cross section of the hickory nut also reveals some major negative characteristics associated with shellbark hickory as compared to pecan. The hickory has both a very thick shuck and shell. At harvest the shuck of the hickory remains woody, clings to the nut inside,  and is difficult to remove from the nut. Pecan nuts fall from the shucks after a good hard freeze. The thick shell of the hickory and the bony partition between kernel halves make extracting nut meat difficult. In contrast, the Kanza pecan shells easily producing a high percentage of kernel halves.    

Wednesday, August 17, 2016

Black-margined aphids create sticky leaves

   This week, I noticed the appearance droplets of sticky sap spotting the leaves of our pecan trees (photo at right). In fact, when standing in the shade of one of our pecan trees, I could feel tiny droplets of plant sap hit my arms and face. It seems we have begun our annual outbreak of pecan aphids and they are covering the tree and everything under the tree's canopy with honeydew.   

     I pulled a few leaves off a tree to look for aphids.  What I found were numerous adults and nymphs. In the photo at left, note that only the adult aphids have wings. The black markings on the outer edge of each wing identifies this insect as a black-margined aphid. The wing-less insects represent immature stages of aphids call nymphs. Note in the photo that there are several sizes of nymphs. Young aphids molt their exoskeletons as they grow larger leaving behind white cast skins on the underside of leaves. There is one cast skin in the photo, can you find it? (upper center of photo).
    Rain is forecast for this weekend and a heavy rainstorm can often cause a dramatic drop in aphid populations. If we do receive significant rain, we will need to spray for pecan weevil next week and if aphid populations persist we probably add an aphicide to our weevil spray.