Tuesday, April 21, 2015

How pecan trees seal off pruning wounds

     Early spring is a good time to prune pecan trees, whether you need trim off lower limbs or make some corrective pruning cuts. Before making any pruning cut, I think it is important to understand how trees are designed to deal with tree wounds.
    First, lets look how a tree deals with healing a wound caused by a broken or dead lateral branch. In the photo at right, a lateral branch has died from lack of sunlight. Look carefully at the branch and you can see the bark is starting to slough off and the wood of the dead branch is starting to decay. However, what is more important to see in this photo is the prominent branch collar that has developed around the base of the dead branch. The red arrow points to the upper edge of live tissue that will grow over the wound that will be created when the dead limb finally rots away.
     When making pruning cuts its always best to work with the tree's natural wound healing strategy. If you prune a limb off at the upper edge of the branch collar, that wound will quickly grow over to seal out wood rotting organisms.  

    Sometimes I'm surprised by the tree wound healing process. The other day I was out in our pecan scionwood orchard and I noticed a tree wound created by cutting scionwood last spring. The original pruning cut was made just above a bud and a new shoot grew from that bud last summer (photo at left).
   The interesting thing I found below the pruning cut was a very distinctive ridge in the bark that angled down away from the new shoot (red arrow). It looks like the tree is trying to develop a branch collar around the pruning wound.
    I took my knife and scratched the bark above and below that bark ridge. Below the ridge the inner bark was green indicating living and growing tissue. Above the ridge was brown and dead tissue.  This summer, the living portions of the bark will continue to grow and the pruning wound will eventually be covered over by new wood.
    Trees do not heal pruning wounds. They simply grow new wood to cover the wound.

Thursday, April 16, 2015

Bud break timing differs between mature and seedling trees

   Recently, I've been posting photos of pecan trees breaking bud. At right is a photo I took this afternoon of a Kanza tree with expanding leaves and barely emerging catkins. Looking the the amount of new growth on this trees has got me thinking its time to start grafting. That was before I went over to look at some of the seedling trees that are scheduled for grafting this year.

    I walked over to a row of Kanza seedlings (rootstock trees grown from Kanza nuts) and was surprised to find that the buds on these head-high trees were only starting to elongate (photo at left). In previous a post, I've shown you the genetic differences in bud break phenology that can be found among pecan cultivars.  Today, by looking a Kanza tree and an entire row of daughter trees, I found that mature, flowering-producing trees start spring growth slightly before juvenile seedling trees. I've also seen this phenomenon occur with fruit trees. A mature apple tree will push out flowers and leaves long before young, non-bearing apple trees start to break bud..
     I might be able to force a 3-flap graft onto the seedling tree shown above but I'd rather wait a bit to start grafting. Waiting will allow me a wider choice of possible grafting methods I can use (I don't start bark grafting until the stock tree has leaves unfurled) and makes finding the right piece of scionwood for each tree a little easier.
   Don't forget to check out the events tab at the top of the page to find a grafting school nearest to you.

Friday, April 10, 2015

Pecan bud break and flowering type

    It seems like spring has come in a hurry and our trees are developing new shoots at a rapid rate. This morning, I photographed emerging buds of several pecan cultivars. I found some cultivars had buds that were just starting to expand while others were already expanding their leaves. I used this variation in bud break timing to create a series of photos that illustrates how protandrous flowering pecan trees (early pollen shed) break bud differently than protogynous flowering cultivars (late pollen shed).

    Today, Surecrop and City Park pecan cultivars were just starting to expand their buds (photo above). At this point in bud development, you really can't see any difference in bud break appearance between the protandrous and protogynous cultivars.

    The buds on Major and Kanza trees had vegetative buds that had expanded to the point you can see leaves about ready to unfurl (photo above). At this point in bud development, the difference between the protandrous Major and protogynous Kanza is readily apparent. Major has pushed out catkins while the catkins on Kanza are still not visible.

     Faith and Lakota trees had leaves that were well developed (photo above). At this point, the protandrous Faith cultivar had well developed catkins while the catkins on the protogynous Lakota cultivar were just starting to emerge from their bud scale covering.
     As your trees break bud this spring, you might want to check out this phenomenon on your pecan trees.

Tuesday, April 7, 2015

Warm night temperatures advance pecan budbreak

     Last night, overnight low temperatures did not drop below 60 F. Suddenly all the trees in the area look like they are bursting with new spring growth. Pecan trees are no different. Today I found catkins emerging on a tree that has a protantrous flowering habit (photo at right).

    The buds on protogynous flowering trees have also advanced with new leaves poised to unfurl (photo at left). Catkins on these trees are not visable at this time but will soon break out of the two narrow, tapered buds that appear on either side of each central vegetative bud.
    Emerging shellbark hickory buds are massive (photo at right). If you look carefully you can spot two catkins poking out from under a bud scale mid-way along the expanded bud.
   The emergence of new growth in the Spring always gets me excited for the coming season. We'll be grafting soon, followed by a long summer of watching this year's nut crop grow and mature.