Thursday, February 21, 2013

Tips for cutting pecan scionwood

   When ever we get decent weather during the month of February we are outside cutting pecan scionwood. The best quality scions are collected from young, vigorous-growing trees (photo at right). A close look at this 'Lakota' tree and you'll find it covered with one-year-old shoots that are 18 to 24 inches long. This kind of shoot growth makes great scions but removing every one-year-old shoot from this tree will also remove the entire 2013 pecan crop.
    As you can see by the shucks that still remain, this 'Lakota' tree produced a good crop of nuts in 2012. So to prevent crop production losses due to scionwood collection, we have developed a scionwood orchard.
   Trees in the scionwood orchard are spaced close--15 ft apart in the row and 30 feet apart between rows. The trees are pruned heavily every year to force the production of long vigorous shoots (photo at left). Each tree now produces hundreds of high quality scions.
    While cutting scions the other day, I thought it would be a good idea to show you a few tips on scionwood collection. Lets start with the perfect piece of wood (photo at right). Great scionwood is relatively straight and has well-formed, prominent buds that are widely spaced along the stem. At each bud node you can see a large primary bud with a smaller secondary bud below. An even smaller tertiary bud can be seen below the secondary bud and just above the leaf scar.
    In forcing strong shoot growth on our scionwood trees, we often collect wood that have stalked buds (photo at left). If you come across any stalked buds on your scions, prune them off before putting the wood into refrigerated storage. This kind of wood still makes good scionwood because of its innate vigor and the fact that there are large secondary buds under each stalked bud.
     When cutting scions, you might notice that the buds near the base of the one-year-old shoot are often smaller and less prominent than buds on the middle portion of the shoot. This occurs most frequently when you cut one-year-old shoots are over 2 feet in length. In addition, the small primary buds found near the base of the shoot are easily knocked off during handling (photo at right). These lower buds are less tightly held to the stem because of apical dominance that was expressed during the growing season by the more prominent buds found near the terminal of the shoot. You can still use this kind of wood to make a successful grafts but you'll find that only secondary buds will break bud and new growth from the scion will take longer to appear (7 to 10 days longer).

    Now lets look at the terminal portion of the shoot. In the photo at left, note the furrows in the stem marked by the red arrows. These furrows tell me that this portion the the stem has a very large pith with only a thin layer of wood under the bark. This kind of wood is never good for grafting. If is difficult to carve and percent take will be poor.  In cutting scions, I always discard the terminal portion of the shoot.

   One problem faced by pecan growers is collecting scions from mature trees. Once a tree goes into full pecan production, new shoot growth is often limited to 4 to 6 inches in length (photo at left). The buds on these shoots are close together and the shoot length is so short its impossible to carve . If you want to collect scions from a mature tree its always best to prune a few limbs the previous year to force vigorous shoot growth. However, in a pinch let me show you a technique for harvesting scions on trees with short one-year old growth.
    Here's a twig I cut from a mature tree. Note I cut off a twig with both one and two-year wood (photo at left). Also note that the one-year wood has prominent buds, while the buds on the two-year wood are long gone (they fell off along with the catkins last spring). However, the two-year wood is larger in diameter providing me with a better spot more making grafting cuts.
      In preparing this scion, I start by pruning off one half of the forked twig and discarding it (photo at right). One interesting thing to note is the pedicle on the end of the discarded twig. This pedicle held a cluster of 3 nuts last fall.
    Next, I cut off the terminal of the shoot and discarded it (photo at left). Cutting off the terminal effectively removes any pistillate flowers that might emerge once the graft takes.
    This leaves me with a crooked scion but one that has plump, healthy buds on the upper end and a good, thick area to make my cuts on the lower end. This scion is not ideal--the two year wood has too many leaf scar bumps in the way of making smooth cuts but I could make this work for a bark graft in a pinch.