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.

Friday, July 17, 2015

Pecan scab sporulation

    Yesterday morning I walked through the orchard checking on the spread of pecan scab. At this point in the season, only cultivars that have a history of severe scab susceptibility are supporting a large number of scab lesions on the fruit. I found bad scab infections on Maramec, Hirschi, Dooley and the clone pictured at right, USDA 75-8-5.
    I collected several nuts from 75-8-5 and placed them in a plastic zip-lock bag to bring inside to photograph. I especially wanted to look at a scab lesion up close, using a dissecting microscope, to see if I could see the scab fungus sporulate. I held the nuts in the plastic bag overnight to provide the high humidity conditions needed to promote the development of pecan scab spores.   

    The photo at left shows the scab lesion located in the center of the nut pictured above. Under magnification the surface of the nut looks like a field of tan-colored pebbles on a base of green shuck. The scab lesion is black and appears somewhat fuzzy.
   In response to the high humidity, that formed inside the plastic bag, the scab fungus developed structures known as conidiophores or translucent stalks that stick up from the surface of the lesion.  These conidiophores give this scab lesion its fuzzy appearance.
    On the ends of each conidiophore, a chain of oval-shaped conidia form. These conidia are the spores are released into the air, spreading the fungus throughout the orchard.
    After this simple experiment in forcing sporulation from a scab lesion, I now know how quickly and easily scab can create new conidiophores and conidia out in the field. I am more than ever convinced that grafting scab resistant pecan cultivars is the best way to fight this disease

Wednesday, July 15, 2015

Disease susceptibility: Mandan and Pawnee

Pawnee, 15 July 2015
    Back in 1984, when Pawnee was released as a new cultivar it was promoted as an early-ripening, scab-resistant pecan. We have since gained decades of experience with this cultivar and have discovered that Pawnee ripens large beautiful pecans early in the Fall. However, Pawnee has turned out to be quite susceptible to pecan scab requiring multiple scab sprays to keep shucks clean. In fact, I photographed a cluster of Pawnee nuts this morning and found not only black pecan  scab lesions but I also found a portion of the shucks were covered with the white powdery mildew fungus (photo at right).

Mandan, 15 July 2015
   Mandan was released in 2009, with similar fanfare--large nut, early ripening, and scab resistant. This morning I also photographed a cluster of Mandan nuts (photo at left). And guess what I found? That's right, pecan scab and powdery mildew. We have only been able to see our Mandan trees bear nuts for 4-5 years now but I have seen enough of this clone to say that Mandan is definitely not scab resisitant.

Friday, July 10, 2015

Spraying for pecan scab

   We received 3.5 inches of rain this past week and as soon as the sun popped out this morning I knew it was time to fight pecan scab. High humidity, warm temperatures and nuts that are rapidly expanding in size all make for perfect conditions for the spread of scab. This morning I walked out to some of our Pawnee trees and found a few small scab lesions on the nuts (photo at right). It was definitely time to take action.
    We sprayed all improved cultivars with Headline fungicide using our airblast sprayer (photo at left).  We did not include an insecticide with this spray because the insecticide we applied for casebearer last month also served to keep fall webworm in check. With the El Nino weather pattern this year, I'm thinking we might get a wet summer this year and we'll need to make additional fungicide applications later this month.

Tuesday, July 7, 2015

Pecans start nut expansion

     The nuts on our pecan trees are finally starting to grow in size. However, pecan cultivars differ in the timing of when the phase of rapid fruit enlargement begins. In the photo at right, I have harvest nuts from three pecan cultivars. Warren 346 is one of the earliest ripening cultivars we have in our collection. Pawnee ripens in late September while Kanza ripens in early October. One of the characteristics of early maturing cultivars is that they start into rapid fruit expansion earlier in the growing season. Note, that by July 6th, the Warren 346 grown larger than Pawnee and even smaller Kanza.

    Cutting open each nut you can see that the size of the ovule (small water filled sack that will grow and develop into pecan kernel) also differs between cultivars. Kanza has a small tear-drop-shaped ovule while the ovule of Warren 346 is nearly 5 times the size. Watching the growth and expansion of the ovule is the best way to judge the development stage of a pecan. If you would like to learn how to cut nuts open to check on kernel development check out this post.

Saturday, July 4, 2015

July 4th graft trimming

    For all those that have attended one of my grafting schools, here's a reminder that this weekend is a good time to trim up new grafts if you haven't already. Although I've been working on trimming grafts for over a month now, I still had a few that still needed attention. The photo at right shows a tree I worked on this morning. Three shoots have grown from the scion of this bark graft and two trunk sprouts have grown out just below the graft union. Time to get out the clippers.
    My first step was to remove all trunk sprouts below the graft union (photo at right).
    Next, I trimed the scion so only one shoot was growing fron the original scionwood stick (photo at right). In this case, the upper most shoot had the greatest diameter so I kept it over the others. Pruning the scion down to one shoot off the scion makes tree training much easier and helps develop dominant central leader.
   The final step in trimming up this graft is to remove the green grafting tape that holds the plastic bag tight around the scion. The scion stick will grow rapidly in diameter this summer and I don't want the tape to girdle the graft. I simply use a knife to cut the tape  but leave the plastic bag and aluminum foil in place.
   Next, I turned my attention to the top of the scion shoot. Stalked buds had formed on the new growth and I carefully removed each one by just pulling them off the tree (photo at right). With all the trimming complete, I tied the new growth to the bamboo stake using flagging tape to make sure I wouldn't lose the graft in a wind storm. And lastly, I placed a deer cage over the tree to keep the critters away.