Thursday, December 7, 2017

Same seed source--big differences in rootstock growth

   When we were harvesting a cultivar trial, I came across a plot of four Major trees that were fairly uniform in size and all bearing a good crops (photo at right). These trees were field grafted back in 1985 to Giles seedling rootstock trees. The grafts were placed at 18-24 inches above the soil surface and after 30+ years you can still see the graft union on each tree (note the abrupt change in bark texture).
    As I walked down the tree row, I noticed significant differences in the diameter of the rootstock as compared to the trunk diameter of the scion (photos above). For tree "A", the Giles rootstock has over-grown the Major scion. Tree "B" has a smooth transition between rootstock and scion. Trees "C" and "D" are more typical of trees grafted with a Major top--the scion overgrows the rootstock.
    Major is a vigorous growing tree, often producing the largest tree in a planting of several cultivars. That's why it so common to find Major scions overgrowing their rootstock. However, I wanted to show you these photos to make two points. First, no matter the seed source for the rootstock, there will always be variation in growth among rootstock trees. Each pecan rootstock tree has a unique genetic composition created by a known mother (in this case Giles) and a unknown father (pollen blown to the stigma on a puff of wind). This variation may cause differences in the appearance of a graft union but it appears to have little impact on the scion's performance and yield.
    The second point I wanted to make is that is not that critical to plant a particular seed source to grow rootstock trees. In northern pecan areas, you should use seed from either local native trees or nuts produced by a northern cultivar. The resulting trees will have the best cold hardiness for your location.  Many years ago, we had some Giles trees growing at the research station that had been propagated by a southern nursery that used a southern pecan cultivar for growing their rootstock trees. In 1989, temperatures dropped to -26 F (-32 C) in mid-December.  The Giles tops survived the cold but the rootstock portion of the tree was killed by the cold. With a dead root system, these tree had to be removed.

Thursday, November 30, 2017

The cost of scab infection

   We've been working hard at harvesting the 2017 pecan crop and I was struck by the obvious impacts pecan scab infection has had on some of our pecan cultivars. At the research station, we have a block of Giles and Chetopa trees, two scab susceptible cultivars. For each cultivar, I collected a nuts from the harvester and arranged them by size for a photograph.

    Each photo  shows 3 normal sized pecans in the top row compared to scab-effected,  smaller nuts in the bottom row.  Although both cultivars showed signs of yield loss (smaller nuts) from scab, Giles looks harder hit.
   Looking back at our pecan scab control program in 2017, I think we made an error in waiting for the appearance of pecan nut casebearer before making our first scab spray. As it turns out, casebearer never developed to a damaging level but pecan scab got a good start on our nut crop in early June. I'm becoming convinced that I need to switch our pest control priorities. Next year, I'll time our June pesticide applications based on scab. If that means applying an insecticide a little early for casebearer, so be it. I'll just have to chose a long residual insecticide like Warrior or Intrepid to handle casebearer.  

Wednesday, November 15, 2017

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).  Sellable 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 signicant 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.

Thursday, November 9, 2017

A mild freeze and pecan leaf fall

Kanza pecans, 2 Nov. 2017

   I don't think I've ever seem pecan trees hold on to their leaves like this year. During most years, we get a hard freeze in early November that causes pecan leaves to drop off the tree in just a few hours. Not this year.
    Temperatures dropped to 27 degrees (F) on a couple of occasions in late October which froze leaf blades but did not kill leaf rachii (photo above). The result of this weather pattern has been that shucks have opened up but the leaves have remained in place (even with frost burned leaflets).
    We have harvested several pecan cultivars this week but have found that the semi-green leaves that cover the ground after tree shaking has made harvest by machine a lot less efficient. It seems that the machine is having a hard time digging out pecans from the still leathery leaves.  After a hard freeze (less than 26 F), leaves turn crispy dry and are ground up by the harvester.
    In time, our harvest problems will pass as colder temperatures are surely on the way. However, a second trip over the orchard with the harvester later this fall will yield far more nuts than in previous years.