Friday, February 27, 2015

Pruning up a young tree

   One of the most common misconceptions pecan tree owners have is that pruning off all lower limbs will force the tree to grow faster and produce nuts sooner. In reality, radical lower-limb removal only serves to retard tree growth and delay nut production.  Instead, I recommend that growers remove lower limbs over a period of several years while maintaining a full canopy of leaves. Let me show you an example.
    The photo at right shows a Faith pecan tree I have growing in my back yard. I've posted photos of pruning this tree in a previous post but now, two years later, I'm ready to make few more cuts. This year I'll be pruning out one of the lowest limbs on this tree (pointed out by yellow arrow) and then turn my attention to thinning out one of the branches located a little higher in the tree (area marked by red circle).

    Lets start with the lowest limb (photo at right). If you look carefully at the "before" photo you can see the largely healed pruning scar on the left side of the trunk. Also, you can see a wound on the remaining low limb where I had made a bench cut in an effort to direct the growth of the lateral limb outwards. But now it was time to remove the entire limb. I used a pruning saw to remove the branch just outside the branch collar.

    Next, I moved up the trunk to the cluster of branches I had circled in red in the photo above. In this close up shot (photo at right), you can see that there are four lateral branches arising from the same area on the central leader.  By the time this tree matures, I hope to have a clear, straight 8 foot tall trunk which means all four of these limbs will be gone at sometime in the future. But for now, I will remove just one.  The limb marked by the red arrow has a narrow branch attachment angle and is growing so upright that it might threaten the dominance of the central leader. Pruning out this limb now will improve overall tree form while giving the tree a chance to heal over the wound before I remove another limb in this area.

    The photo at left gives you a better idea of how I pruned out the upright-growing limb. By cutting at an outward sloping angle just outside the branch collar, I left the smallest possible pruning wound. In less than two years this wound should be completely callused over.
     The photo below gives you a before and after look at this year's pruning effort. It's easy to spot where I removed the low limb but harder to spot where I removed the upright branch further up the trunk. And that's exactly why the slow approach to lower branch pruning is best. By just pruning out a  couple of limbs this year,  the tree's overall canopy was left largely intact.

Friday, February 20, 2015

Identifying Peruque

   When we harvested our Peruque crop this past fall I noticed that the nuts didn't have their characteristic "bottom heavy" appearance. In the photo at right, note that the nut harvested in 2013 is wider at the base than near the apex. This general nut shape is termed "ovate" or egg-shaped and it is the usually shape for Peruque. But in 2014, our Peruque nuts took on a more oval shape where the nut's base and top of the nut were just about the same size.
   A quick look at the Peruque nuts we produced this year would have some question if we really had the right cultivar propagated in our orchard. But over-all nut shape can be influenced by weather patterns and 2014 provided the the perfect example. If soil water becomes limited during the later stages of nut expansion the base of a nut will become smaller in diameter. A period of dry weather in late July was the reason our Peruque nuts did not develop their normal "bottom-heavy" shape in 2014.
   Over-all nut shape is not the only way to identify pecan cultivars. Peruque nuts have four, very-characteristic corners on the shell just below the shell's apex. The photo at right shows the same two nuts as seen above but photographed looking down on the top of each nut. On each nut I've drawn a red square whose corners point to the four corners on the shell.  

    Cracking open a nut is also a good way to gather further evidence of cultivar identity. In cracking Peruque you should find a extremely thin shell. Once the kernels are extracted Peruque has two characteristics that can be used to help verify the cultivar. In the photo at right, note that the dorsal groves of Peruque kernels form a very distinctive "V" shape unlike most pecan cultivars that have parallel dorsal groves. Next, note the deep cleft in each kernel half located at the top of the nut meat. Many pecan cultivars have a small cleft at the top of the kernel but the cleft found in Peruque extends deeper than most.

Wednesday, February 11, 2015

Why young tree training is so important.

   This week I traveled to Georgia to attend a meeting of Pecan scientists and I was able to visit a couple of pecan orchards. Pecan trees in Georgia tend to have short trunks and a spreading canopy (photo at right). Back before the invention of pecan tree shakers, trees with a spreading canopy were preferred by the young men charged with climbing the tree to flail nuts out of the trees during harvest. But with modern tree shaking equipment, short-trunked trees are shook one major limb at a time. But having to make multiple shakes on a single tree can slow down harvest.

   When I took a closer look at the large tree  in the photo above, I was surprised to find so many pruning mistakes. In the photo at left, you can see several rotten spots on the tree--all the result of improper limb removal. It looks like several limbs had broken out of the tree due to poor limb attachment angles (narrow crotches). In other cases it looks like proper techniques for limb removal were not followed and the tree had a hard time sealing over the resulting tree wound. If this tree had been trained 50 years ago to a single (and taller) trunk with wide-angled lateral limbs many of these wood rots could have been avoided.

   Later in my trip to Georgia, I came across an orchard with the largest collection of poorly trained trees I have ever seen. 
Split trunk, the result of a narrow crotch
     The photo at left and the ones posted below serve as just a few examples of trees in this orchard that will present the grower with long term tree structural problems. To avoid misshaped trees like the ones pictured here, make sure you start training your pecan trees at a young age. It is much easier to correct poor tree form with a pair of hand clippers than it is to repair broken trees with a chainsaw.
   For detailed instructions on tree training go to my blog series entitled "Training young trees".

Top split out at bark inclusion

No central leader
Split out limb scar, weak central leader
Narrow crotch may lead to split trunk in the future 
Low limbs arising from the same spot on trunk

Monday, February 9, 2015

Choosing a grafting knife

    At this time of year, most avid gardeners are pouring over seed or nursery catalogs and dreaming about the spring planting season. For me, planning spring activities means cutting pecan scionwood and making sure my grafting box is well stocked with the proper tools and supplies. One of the most important tools for any grafter is a good grafting knife. Lets take a look at some the options.
   All knives suited for grafting pecans have two things in common. First, the blade has the "lamb's foot" shape that features a straight cutting edge and a sharp point. Secondly, the knife blade is beveled on one side and flat on the other. This means a grafting knife is sharped on the beveled side only, much like you would sharpen a chisel or plane blade.
    The first choice to make in selecting a grafting knife is to decide if you prefer a folding knife or a knife with stationary blade (photo at right: folding on left, stationary at right). I prefer using a folding knife because I can easily protect the finely honed cutting edge by closing the knife before walking to the next tree.
   Over the years I've collected several grafting knives. The photo at left shows four grafting knives that range in price from $16.00 to $113.00. From left to right these knives are:
     1. Antonini, model 5036L, high carbon steel, Italy, $28
    2. Barnel, model B6050,  high carbon steel, Solingen Germany, $65
    3. Tina, model 605T, high carbon steel, Germany, $113
    4. Victorinox, Grafting knife, stainless steel, Switzerland, $16

    First off, I prefer a knife with a wooden handle because I can keep a firmer grip on the handle while grafting. Nylon handled knives seem to slide around in my hand. Also, notice how the knife blade is attached to the handle of each knife above. With the Tina and Antonini knives, the cutting edge starts adjacent to the end of the handle. In contrast, Barnel and Victorinox have cutting edges that start well above the handle. Over the years, I have found that I can keep better control of the knife when the cutting edge of the blade is closer to the end of the handle and my hand.
    In choosing a grafting knife, the type of steel used to make the blade impacts how long the knife stays sharp and how easy the blade is to resharpen. Grafting knives are made with either high carbon steel or stainless steel blades. The photo at right shows two knifes built by the same manufacturer, A.E. Coltellerie Inc. of Maniago, Italy. The knife on the left has a high carbon steel blade, kotibe wood handle and is sold under the company's brand, Antonini. The knife on the right has a stainless steel blade, rosewood handle and is marketed in the US by A.M. Leonard Inc. High carbon steel blades are easier to sharpen and hold that edge longer than stainless steel blades. The only advantage stainless steel has over high carbon steel is that it doesn't rust. I personally prefer high carbon steel blades for grafting and save my stainless steel knives for cutting apples, frequently sampled from my wife's orchard.
   Often overlooked in choosing a grafting knife is how well the handle fits in your hand. The photo at left gives you an idea of how much handle thickness can vary between manufactures. In the photo, a Tina knife is shown on the far left, the Antonini knife is in the center, and the Barnel knife is on the right side.
    I have been using a Tina knife for grafting pecan trees for 35 years and have come to love that knife. However, the I've noticed that as my hands get older, my fingers seem to cramp up after a long day of grafting. I'm thinking that a little larger diameter handle might help with my hand fatigue. In handling the Antonini and Barnel knives, I found the Antonini just about right but the Barnel felt uncomfortably large. The bottom line is that you need to find a knife that fits your hand. I'll be giving the Antonini knife a good work out this coming grafting season to see how my hands hold up.

Wednesday, February 4, 2015

Pecan scab on dormant twigs

    I spent some time this morning looking over the trees in our pecan scionwood block. While checking on the quantity and quality of the scions we will begin harvesting later this month, I noticed an abundance of pecan scab lesions on the twigs of a Hirschi tree (photo at right). When thinking about pecan scab, most folks picture pecan shucks covered with black spots. However the scab fungus can infect both leaves and twigs.
   During the winter months, you can check your trees for scab lesions on the one-year-old twigs. The amount of scab seen on the twig pictured at right is a good indication that Hirschi is very susceptible to the disease. All of those black lesions will be releasing spores next spring that will start new infections on leaves, nuts, and new shoots.

   For many scab susceptible cultivars, scab lesions are not as large or numerous as what I found on Hirschi. Pictured at left are twigs cut from two northern pecan cultivars. Note the small black spots on theses twigs. Although the number and size of lesions on these two twigs look similar, Chetopa nuts are only slightly susceptible to scab. In contrast, Peruque nuts are moderately susceptible and are often troubled by nut scab. In other words, you can not predict the severity of future nut infections by looking at twig lesions.

    While checking for scab lesions on twigs, I decided to look at Pawnee as compared to Mandan. When Pawnee was released in 1984 it was touted as a scab free cultivar. After testing this cultivar at our location in Kansas, we found scab did infect Pawnee nuts and required multiple fungicide application to control the disease.
  In 2009, the USDA released Mandan and promoted this new cultivar as being scab resistant. If you look at the twigs pictured at right, you will note that both Pawnee and Mandan have scab lesions. This tells me that Mandan is not scab resistant as promoted. However, we have yet to produce enough nuts on our young Mandan trees to determine how susceptible this cultivar is to nut scab.  

Sunday, February 1, 2015

The pecan tree's backup plan

    Look carefully at the buds on a one-year-old pecan shoot. Above each leaf scar (the heart-shaped scar on a dormant stem) is a row of buds that range in size from the largest at the top to the smallest nestled tightly against the leaf scar (photo at left).
    The primary bud is the most prominent in the group and will be the bud that breaks opens and grows during the spring flush of growth. Inside the bud is a vegetative shoot flanked on each side by a set of catkins (male flowers). If all goes well, the primary bud grows and the smaller buds below it will remain dormant.
    However, the tree creates secondary, tertiary and quaternary buds just in case something happens to injury or destroy the primary bud's new growth. A late spring frost, a freak hail storm, or even an outbreak of sawflies can destroy the tree's first attempts at new spring growth. That's when the secondary bud comes into play. The secondary bud will start growth in response to the lost of the primary bud. We saw this happen just last year in response to a late spring freeze.
     Back in 2007, I was really glad that pecan trees have a built in back-up plan for restarting growth following the loss of new growing points. We established a new orchard using container grown trees in the fall of 2006. On Easter weekend of 2007, we experienced bone chilling cold that froze all the emerging green tissues off the young trees. A couple of weeks later, secondary buds broke and the trees resumed building new shoots and leaves. Later that summer, the Neosho river spilled over its banks and we experienced the second highest flood on record. The flood waters were so deep that they completely covered the newly established trees and killed all green tissues. Once the flood receded, tertiary and quaternary buds broke and young trees struggled back to life.