Thursday, July 30, 2015

Be careful to remove the right buds during young tree training

   In several posts on this blog, I have stresses the importance of removing stalked buds from rapidly growing young trees to encourage the growth of a strong central leader tree.  The photo at right shows the terminal portion of a tree I grafted this past spring. Note that the primary buds in each leaf axil have already formed a long stalked bud. By removing all these primary buds near the apex of the tree, I can force the tree to remain focused on growing a single central leader. Pruning out stalked primary buds effectively delays the tree from developing lateral branches in the pruned area for 3-4 weeks. This allows the central leader to grow taller, staying well above later developing lateral branches.
    However, my emphasis on removing stalked buds may have caused confusion among some growers. The photo at left shows the same tree as the one pictured above. However, this photo shows the central leader of my new graft about 2 feet below the apex. Here you will note a short stump hovering over a growing bud in each leaf axil. This stump was left behind when I pruned out a stalked, primary bud 3 weeks earlier. Now the secondary buds are starting to grow out, looking like slightly shorter versions of those dreaded stalked buds. Here's where the confusion comes in. Don't feel the urge to rip off these secondary buds just because they appear to be stalked.
    These secondary buds were fully sessile when they were formed. But at this point in time, the secondary buds are pushing out to grow new lateral branches. And since these new shoots are forming about 2 feet below the central leader's terminal, you should let them grow out.
   The art of young tree training is an act of making sure a tree achieves balance between growth of the central leader and the development wide-angled lateral branches. Allowing secondary buds to grow and produce laterals is an important part of that art.    

Wednesday, July 29, 2015

Fall webworm: Nobody's home

    Driving down the highway you'll see numerous webs up in trees all created by Fall webworm larvae. These caterpillars are general leaf feeders that colonize numerous hardwood tree species including pecan, hickory, black walnut, persimmon, and green ash. If you get up close to one the the dirty white webs, you will note that all the foliage inside the web has been devoured by the caterpillars (photo above). Leaves outside the web are still green and untouched. 

    By late July, all of the webs have been vacated. A closer look into the web will reveal nothing but the white fuzzy exoskeletons discarded by molting caterpillars and black balls of insect frass (photo at left). Once the caterpillars reach maturity, they drop out of the web and settle down in the leaf litter on the ground. The caterpillars then spin a cocoon to begin the process of changing into an adult moth.
   At this point in time we are between generations. The second summer flight of fall webworm moths usually starts in early to mid-August. Judging from the number of first generation colonies I've seen up and down the road, the second generation should be ever larger.  Fortunately, we will be spraying our trees for stinkbugs and pecan weevils during the month of August and these sprays will keep the second generation out of our pecan grove.  

Thursday, July 23, 2015

A preview to nut maturity date

16 July 2015
     Last week, I collected group of well known pecan cultivars to check on the progress of nut development. Sometime during the month of July, all pecan cultivars enter a phase of rapid nut expansion. In a previous post, I outlined the phenology of pecan fruit development and made the point that early-ripening cultivars start sizing earlier in the year, fill their kernel earlier in August and take less time ripen following full kernel development.  
    In the photo above, I've arranged 5 cultivars in order of the expected ripening date this fall. Faith will split shuck in late September while Stuart won't mature until late October.
   By cutting open each of these nuts, you can see that the kernel is just starting to develop inside each of these nuts (photo at right). The Faith nut has the most advanced kernel and is in the large heart stage. Kanza and Oswego have developed small heart shaped kernels while Giles and Stuart kernels are still oval in shape. Rapid nut expansion doesn't really start until the kernel takes on the small heart shape. This means, by mid-July, Giles and Stuart are already significantly behind in the race towards nut maturity. 

16 August 2015
   Now, let's look at a few cultivars that we haven't had years to study (photo at left). The first thing I notice is that two cultivars, Surecrop and 75-8-5 are much plumper than the others. City Park, a large blocky nut at harvest, looks small and thin at this point in the season.  

       I cut these nuts open to check on kernel development and allow me to compare this second set of nuts with the first.  USDA 75-8-5 had the largest kernel growing to 1/4 water stage. Surecrop, Lakota, and Gardner (sorry for the bad cut on Gardner) were all in the large heart stage. City Park was just approaching the small heart stage.
   What does all this mean? It means that USDA 75-8-5 will ripen in late September at our location.  Surecrop, Lakota, and Gardner will ripen in early October. City Park will be the latest to ripen sometime in mid-October.

Monday, July 20, 2015

Young tree training: When the central leader grows too fast

   In training pecan trees, you'll find that not all trees grow the way pictured in text books. The tree, pictured at right, is a great example of a young pecan tree that grew too tall, too fast. With the summer wind blowing constantly from the south, the heavy growth of leaves at the top of the tree has proven too much for the narrow trunk to hold upright. The result is a tree that bends over, pointing north.
    This is a tree that never developed a good balance between a strong central leader and lower lateral branches.  I placed a 5 foot ladder in the photo to give you an idea how tall this tree actually is. The tree was grafted at about 3 feet high (the union is marked with white paint). The graft grew strongly but failed to sprout lateral branches along the leader in an area 3-4 feet above the graft union. It was this lack of lower lateral branch formation that ultimately caused the tree to become top heavy and start to bend over.

    Let's take a closer look at the top of this tree (photo at left). I've marked the direction of the summer winds and you can see that the once proud central leader is now growing at a 45 degree angle. However, the tree has recognized that the leader has lost its dominate position and a lateral shoot has started to grow in a position to become the new leader (red arrow).

   To force this tree to grow back into balance, I decided some radical pruning was needed. The photos above illustrate the cuts I made to define a new central leader. The photo on the left shows the tree before I made any cuts. I decided to remove the leaning portion of the tree by pruning the former leader back to the lateral shoot pointed out by the red arrow. After cutting off the top of the tree I was left with two strongly upright shoots (center photo). To create a new central leader I pruned off the lower of the two upright shoots (right side photo).

   After making just two pruning cuts I was left with a tree that was growing in the right direction (photo at right). However, these pruning cuts don't guarantee that new lateral branches will sprout along the lower portion of the trunk. I'll need to watch this tree over the next couple of weeks. If I don't get any lateral sprouting, I'll tip prune the central leader to slow its growth and encourage lateral growth.