Friday, July 19, 2019

Graft position impacts pecan scion growth rate

     Earlier this year, I wrote about top-working a young tree by grafting both the central leader and three side limbs. Just to remind you of my grafting efforts, the photo at right shows the tree right after I completed the grafting process. By mid-summer all 4 grafts have grown new shoots but at very different rates. Watching this tree grow has taught me a valuable lesson about the nature of apical dominance in pecan trees.
     By mid July, I had made several trips to this tree to trim off trunk sprouts and to prune each graft to a single growing shoot (photo at left).  Each new shoot has been tied to its associated bamboo stake to prevent wind damage. What impressed me most about this tree is the fact that the scion placed on the central leader has far out grown the scions place on side limbs. The new shoot growing from the central leader is near 3 feet in length and still growing while side-limb scions had shoots less than half that length.
    The difference in growth rate can also be seen by comparing the diameters of the scions. The photo above shows the growth of the scion on the central leader as compared to one of the side shoots. I placed a quarter in front of each scion to give you a sense of scale (a US 25 cent coin is roughly 1 inch or 25mm in diameter).  Remember, when I placed the grafts on the tree the scions were roughly 7/16 inch or 11mm in diameter. As the scion grows in length, it also grows in diameter. What is especially impressive about the growth of the scion on the central leader is how quickly the scion will cover over the wound created by the grafting process.
   Obviously, a pecan tree will expend most of its energy to quickly re-establish the central leader. This is why, when top-working,  a bark graft is traditionally placed it on the central leader. Although the grafts placed on side limbs were successful, these limbs will continue to grow at a slower pace and will eventually become completely dominated by the scion growing on the central leader.
   Many novice growers dream of growing several pecan cultivars by limb grafting several types of scions on the same tree. Yes, multiple grafts can be made but a graft placed on the central leader will always dominate the rest of the tree. This is why it is always best to graft a single cultivar on a tree and make that graft on the tree's central leader.   

Tuesday, July 16, 2019

Squirrel kills established graft


   While working in my pecan orchard today, I noticed a young tree with brown, dried-up leaves (photo at right). This is a tree I top-worked a couple of years ago (graft union marked with white paint) and it looks like only the graft was effected. Below the graft union the trunk is sprouting all kinds of new shoots. But what caused this graft to die in mid summer? Let's take a closer look.
    Just above the graft union the bark of the scion has been stripped off (photo at left). This kind of bark stripping is caused by fox squirrels looking for nutrition from the cambium of tree stems. damage occurs in late winter or early spring especially during seasons following a short nut crop (the 2018 pecan crop was tiny).  Squirrels prefer to strip smooth barked pecan limbs and my vigorously growing graft must have looked especially delicious.
    The tree still had a thin strip of live bark on the side of the tree protected by my tree training stake (photo at right). This bark strip provided enough water to the upper portion of the tree to allow the graft to bud out and begin new growth this past spring. However, as the heat of summer arrived, the tree was unable to keep enough water and  nutrients flowing to the top of the tree and it finally wilted and died.
    
   Below the graft union I had sprouts growing everywhere (photo at left). Since I lost the entire top of this tree I searched though all these trunk sprouts to find a good candidate to be my new central leader.
   Once I identified my new main stem, I pruned off all competing stems and cut the trunk at a 30 degree angle just like I was training a bark graft (photo at right).

  Until a trunk sprout grows some new wood for a couple of years, the joint between old trunk and new sprout is fairly weak. To prevent possible wind breakage, I attached a 8-foot-long pole to the side of the tree and tied the new shoot to it.
    Next spring, I'll re-graft this tree on my new central leader.

Thursday, July 11, 2019

Making my third disease control spray

    This summer had been wet and humid in SE Kansas. Pop-up thunderstorms have been frequent and those wet spots in the pecan grove never seem to dry up completely. Needless to say, this has been an ideal year for the spread of pecan diseases. Today, I was out looking at some un-managed pecan trees and I found a tree with a terrible case of pecan scab (photo at right). With an infection this bad in early July, I can guarantee you that these nuts will never yield salable pecans in the Fall. Spraying pecans with a well established scab infection like the one pictured will not cure this disease. Fungicides are only effective in preventing disease infection. This is why I've tried to stay ahead of scab this year by making multiple fungicide applications.
    I made my third fungicide application today.


    Insect pressure on our pecan trees in the area has been light. Today, I noticed my first Fall webworm colony (photo at left). The dirty white web located near the bottom of this native tree's canopy contains larvae from the first summer generation of Fall webworm. A second generation usually appears in August at a time we are often spraying for pecan weevil.

Tuesday, July 9, 2019

Pruning a young pecan tree back into balance

     During the cool morning hours I've been checking grafts and summer pruning young trees. Today, I came across the tree pictured at right and decided it needed to be pruned into a more balance tree shape. In general, this tree still had a well defined central leader but had one vigorous branch seemingly growing out of place. On closer investigation, I also found the top of the tree covered with stalked buds and a limb growing on the right side of the tree that had developed an over abundance of new shoots. Armed with just a pair of pruning shears, I quickly reshaped this tree.
    I started by taking a closer look at that vigorous side shoot. Tracing the limb back to where in connects to the trunk. I found the diameter of the side shoot rivaled that of the central leader (photo at left). To slow the growth of this shoot, I just need to follow the "2 foot rule" of summer pruning and limit the new growth of side shoot to 24 inches.
    When pruning back a side shoot, I always prune to a downwards pointing bud (photo at right). When this bud breaks, the new growth will be directed outwards rather that upwards to compete with the central leader.
     On the other side of the tree, I just needed to thin out some of the excess growth. Here, I pruned out all upwards growing shoots leaving only outward growing branches (photo at left).
    Next, I moved to the top of the tree. The photo at right  reveals numerous stalked buds have broken bud and have grown 6 to 8 inches in length. Left to grow, all these stalked-bud shoots would create a bushy terminal with no well defined central shoot. All this new growth at the top of the tree will make the tree top heavy and cause it to bend over from the weight (to see an example, check this post).
 
     Moving up the entire central leader, I used my clippers to remove every stalked-bud shoot (photo at left).  When I make these cuts, I make sure that I don't injury the secondary bud just below the staked bud.
 
    The photos above present a before and after look at my young Kanza tree. Summer pruning is a good way to keep pecan tree growing into a strong central leader tree.  I have found it an invaluable tool for training young trees.