Tuesday, June 30, 2015

Trimming up a bark graft placed on a stump sprout

   A couple of years ago we cut down several trees in our pecan scionwood orchard to make room for some new cultivars. Our idea was to cut a tree at ground level, allow it send up stump sprouts, thin the sprouts down to one strong-growing shoot, then graft that shoot the following year. The photo at right shows you one of the grafts I  made on a stump sprout this past spring. One one downsides about grafting a stump sprout is that for several years the tree will continue sending up new sprouts all around the outside of the stump. In the photo a profusion new shoots has grown around the base of my graft.
   The first thing I did was the break out my gas powered weed trimmer and carefully cut off all the new stump sprouts at ground level. You need to have a steady hand and a good eye to make sure you cut just unwanted sprouts and not injure the bark of the stem you are saving. Of course you can use hand clippers to do the same job, but I have found that a good strong string in my weed trimmer actually does a better job of cutting new shoots off at ground level or even a little below.
    The photo at left shows the tree once all the stump sprouts have been removed.

     After trimming off all sprouts that were growing on the trunk below the graft, I turned my attention to the graft itself (photo at right). On this graft, three shoots have developed from the scion. One shoot grew from the upper scion bud while two shoots developed from the lower scion bud. At this time of year I like to choose a single shoot growing from the scion to become my new central leader.
    I first looked at the shoot growing from the upper scion bud (photo at left). This shoot had a very confused growth pattern and was cover with long lateral shoots developed from the growth of stalked buds. This shoot looked like it would be difficult to train so I  decided to prune this shoot off immediately.

   After pruning the scion back to the two  lower shoots (photo at right). I could see that either one of these shoots would make a good central leader. The shoot on the left had a slightly larger diameter so I chose to make it my new central leader while pruning out the other.

    When you graft onto a stump sprout there is a lot of root energy pushing the graft to grow extremely fast. As a result the tree will develop stalked buds a every leaf axil (photo at left). Now that I had pruned the tree down to a single shoot, I carefully pulled off every stalked bud.

   Once I completed all the pruning, I used flagging tape to tie the shoot to my bamboo stake (photo at right). I also cut off the small piece of grafting tape that held the plastic bag tightly around the scion. I don't want any possibility of girdling such a fast growing graft.
   My final step was to replace the deer cage over the graft to prevent browsing injury.

Friday, June 26, 2015

Shaping a young tree with summer pruning

      This month I revisited a young tree I had pruned during the dormant season (photo at right). I was very interested to see how the tree reacted to my earlier pruning cuts and just where and how the new branch growth would develop in the spring.
   Here's a photo (at left) of the same tree--after pruning in March and once the tree has grown new shoots and leaves in June.  When I first pruned this tree, the only lateral branches that had good wide-angled branches attachments were in an area right above the graft union (near the blue tape). Above that, I had 3 1/2 feet of clear central leader. This is definitely not an ideal situation. This tree needs lateral branches to help balance the tree and promote trunk diameter growth.
   As you can see, the short lateral branches I left on the lower portion of the tree burst forth grew over two feet in length. At the top of the tree, I still have a central leader but several strong lateral branches have developed just below. These are growing rapidly and are starting to compete with the leader for sunlight. In the middle portion of the main trunk, I have some lateral branches forming but they growing with less vigor. To shape this tree further, I made several summer pruning cuts to help direct the trees growth into the summer.

    I started by working on the bottom of the tree (photo at right). The yellow arrow points to a rapidly growing shoot that originated with one of the short laterals left during the dormant pruning process. To prevent this shoot from overtaking and shading out weaker shoots above, I cut the shoot back to an outward-facing bud. 
   The red arrow points to a shoot that originated from a bud on the main trunk. This shoot has grown nearly two feet in length, so I decided to pinch out the terminal and force the branch to pause it's extension growth, mature remaining leaves, and build shoot diameter.
   These were not the only lateral branches I pruned. I made similar cuts to lateral shoots around the entire tree.

   At the top of the tree, I followed the 2-foot rule and pruned the terminals of lateral branches below the central leader. I also spent some time to remove all the stalked buds I found growing in each leaf axil on the central leader. Red arrows in the photo at left point to several of these stalked buds and the comparison photo shows the central leader after all the buds have been removed.

   The photo at right shows the entire tree after summer pruning. This tree illustrates key principles of directive summer pruning: Encourage the growth of a central leader, promote lateral limb formation, but keep lateral extension growth in check.

Tuesday, June 23, 2015

Topworking a large pecan tree: Graft aftercare

    Last month, I showed you how I went about top-working a fairly large pecan tree. Using a hydradulic lift, I placed bark grafts on nine major limbs throughout the tree's canopy. Today, I went back to the tree and found that all nine grafts had been successful but they were buried in a profusion of brushy growth (photo at right).  Three bamboo stakes, attached at the top of the tree during grafting, were the only visible clue that I had grafted this tree 7 weeks ago.
    I moved the hydraulic lift up to the tree and immediately started trimming off all trunk sprouts below each graft. It wasn't long until I had the ground littered with green pecan shoots. Once I could see the scions, I found that each scion had at least two shoots growing from the original scion stick (photo at left). Many of the new scion shoots had already grown 18 inches in length so I decided to replace my short bird perches with longer bamboo stakes.
   Once the bamboo stake was firmly taped to the tree, I trimmed the scion down to one shoot (photo at right). I then tied that single shoot to the bamboo stake using engineer's flagging tape. I also used my knife to cut off the green grafting tape that holds the plastic bag around the scion. These grafts are growing extremely fast and I don't want the tape to girdle the scion.
   I repeated this process for all nine grafts I had made on this tree.
    Once I finished all necessary pruning and training, I moved the hydraulic lift back away from the tree to see the results of my handiwork.  In the photo at left, you can clearly see some of the grafts I made and the bamboo poles that support those grafts. If you compare this photo to the one at the top of this post, you can also see just how many trunk sprouts I had to remove.  I have left several small side limbs on this tree to provide shade for the trunk to prevent sun-scald.
     I'll need to return to this tree in 4-6 weeks. By that time, more trunk sprouts will appear and the grafts will need addition ties to the stakes. I surely don't want to lose any of these grafts to breakage in a wind storm.

Friday, June 19, 2015

Fall webworm makes an appearance

    While scouting our trees for pecan nut casebearer we have discovered a few new colonies of fall webworm (photo at right). This is the first of two generations that will make an appearance during the growing season. A second generation will hit in mid-August.

    Fall webworm caterpillars always appear in a large group and surround themselves in white webbing. The spinning of the web starts immediately after egg hatch. In the photo at right, a recently hatched webworm colony has eaten all the green tissue from the terminal leaflet and covered that leaflet in webbing. These insects web over the area in which they are feeding to protect themselves from potential predators and parasites. As the larvae grow in size, the amount of leaves needed to support the colony increases and the size of the web grows. 
    Female webworm moths lay their eggs on the underside of pecan leaves. The dime-sized egg masses are covered with white, fluffy scales deposited by the female to confuse egg parasites. In the photo at right, I've  turned over the leaf pictured above so you can see the remnants of the eggs mass. At the tip of the brown leaflet the white fuzzy stuff left behind after the eggs have hatched.
   At this time, it it two early to tell if we'll see an outbreak of these insects this summer. We will need to keep watching.

Thursday, June 18, 2015

Summer pruning last year's bark graft.

    Earlier this year, I posted some photos on how I pruned a 2014 bark graft during the dormant season. At that time, I pruned the top portion of the tree to define a strong central leader. Now, three month later, I've returned to that same tree to find the central leader has disappeared again (photo at right).  The top of the tree has become a ball of leaves and branches. The central portion of the new central leader is almost devoid of leaves, while the bottom portion of the tree below the graft is just a mess of brushy growth. This tree illustrates exactly why dormant pruning alone does not ensure good tree form. 
    In summer pruning this tree, I have two objectives--to redefine a central leader and to promote new branch formation in the central portion  of the tree.
    I started at the top of the tree (photo at left). If you look carefully at the photo you can see that I do, indeed, have a central leader but the central leader is suffering from intense competition from rapidly growing lateral branches just below. This is where the 2-foot rule comes into play. I pruned off all lateral branches within the top two feet of the central leader then tip pruned the laterals below that.
    If you look at the lower portion of the stem pictured at left, you can see that there are several buds trying to break that can eventually form branches to fill this naked portion of the trunk. Pruning the top of this tree will actually stimulate these bud to grow out and I'll end up with a more balanced tree.

    The photo at right shows the tree once I finished all my pruning. You can see the central leader once again and I have heavily pruned the brushy growth below the graft union.  Pruning a lot of material off below the graft should stimulate growth of the graft and promote those mid-stem buds to break and form new branches.
    I didn't cut off all the growth below the graft because  a sudden exposure to full sun can cause sunscald on the lower trunk. Once the graft fills out with new branches and those branches start providing some shade to the trunk, I will start removing all branches below the graft union.
   Three of four weeks from now, I'll need to return to this tree for additional summer pruning. I've never met a young pecan tree that didn't need additional directive pruning all through the summer. I'm sure to find some stalked buds ton remove.

Tuesday, June 16, 2015

Spraying for scab

   With the over-abundance of rain we have been receiving lately, I've been concerned with the spread of pecan scab onto this year's nut crop. It took me a little while to find active scab lesions this early in the pecan season. When I drove our hydraulic lift over to a Maramec tree, I knew I could find scab on this super, scab-susceptible cultivar.
   After some searching in the canopy, I found a few leaflets spotted with scab (photo at right). Notice that the disease seems to be confined to the youngest leaf on the terminal and the youngest leaflets on the leaf. Since scab infects rapidly growing tissues, is seems likely that scab infected this leaf during pollination season during last month's rainy period.
   The point of finding scab on leaves is to verify that the disease is present and ready to infect young nuts. As the nuts start to grow in the later half of this month, they will become more susceptible to the disease. Unfortunately, the weather man has promised us and entire week of rain--great for scab, terrible for making scab sprays. 

    This morning we had a break in the rain showers and I even saw the sun shine for a minute or two. So we decided to spray our high-value pecan cultivars (photo at left). I knew there was a threat of rain in the afternoon so I choose to use a systemic fungicide that could provide scab protection once the fungicide entered plant tissues. Today, we applied Headline fungicide and added an insecticide to limit the casebearer population. We also added a high quality spreader-sticker to make sure we got good spray coverage.  

Monday, June 15, 2015

Post-pollination nut drop

       Every spring we scout for pecan nut casebearer damage starting shortly after the end of the pollination season. While I'm up in the canopy searching for casebearer, I have noticed that a certain percentage of  flowers simply drop from the tree. I even found what looks like a perfectly normal pistillate flower dropped off and resting on a leaf (photo at left).

      During the the month of May (pollination season in SE Kansas), we experienced several extended periods of rainy weather. Several growers have been concerned that the wet weather inhibited pollination and nuts are dropping due to a lack of proper pollination. The nut clusters pictured above were from the same tree. The photo on the left has two pistillate flowers that are drying up and are ready to drop off. Only one healthy nut remains. In contrast, the nut cluster on the right has five healthy nuts. If rain was a factor in nut drop this year, all pistillate flowers clusters on a single tree would be showing signs of poor pollination. 

   There are actually two types of pollination season nut abortions. The first occurs early, during pollination. A pecan shoot that has insufficient resources can create a entire cluster of small, ill-formed pistillate flowers. These flowers often fall off right in the middle of pollination season. Later, the dried up peduncle will also fall off (photo above left). The second period of nut loss occurs after pollination has been completed.  In this case, what looks like healthy flowers drop from the tree sometimes leaving the entire peduncle bare (photo above right).

   One of the most common types of nut abortion I have seen is the dropping off of terminal flowers in the cluster (photo at right). As a tree creates a new pistillate flower cluster, nutlets are formed from base of the peduncle to the terminal. As pistillate flowers are formed, a flowering shoot can simply "run out of gas" and create small or ill-formed flowers at the cluster's terminal.  What ends up looking like a lack of pollination, is actually nut abortion caused by a weak female flower. Although weak female flowers usually occur at the terminal of a cluster, poorly formed flowers can occur anywhere in the cluster (photo above right)  

    We've recorded post-pollination nut drop for a period of several years and noticed some definite trends. In the graph at right, I've plotted the number of nuts per cluster over time (the month of June). Notice that during odd-numbered years, cluster counts start off high but dropped off sharply. During even-numbered years, trees produced fewer
nuts/cluster but suffered less nut drop. Switching over to yield data for those same 6 years (table at right), we find that odd-numbered years were high crop load years while even-number year produced lesser crops.
    Taken together, these two data sets tell me that pecan trees may have a way of regulating crop load that has nothing to do with pollination. If a tree produces an excess of pistillate flowers ("on" years) post-pollination nut drop will appear severe. In contrast, trees during "off" years seem to want to hang on to every flower they can. 
    This year, our groves are experiencing an "on" year. That might be why we are noticing more post-pollination nut drop. 

Monday, June 8, 2015

First evidence of pecan nut casebearer activity

   Every spring we monitor the development of the first summer generation of pecan nut casebearer. This morning I looked at 300 nut clusters in our native grove and found a single nut that displayed the tell-tale signs of casebearer feeding (photo at right). Judging from the light tan color of the frass pile, the lowest nut in the cluster was attached very recently. The frass pile will turn dark brown as it sits exposed to the weather. Look carefully and you can see fine silken threads that extend from the frass pile to the the peduncle of the nut cluster. These threads serve to keep the nut attached to the tree while the insect feeds inside.
    I like to wait until we record 2 to 3 percent damage before applying an insecticide to control this pest. With only a single damaged nut found, its still too early to spray. Keep up to date on our latest casebearer observations by clicking on the casebearer tab above. We scout our trees every Monday, Wednesday, and Friday

Friday, June 5, 2015

Mandan performance in northern pecan states

    Mandan is a relatively new pecan cultivar that, on paper, looks perfect for northern pecan growers. In past blog posts, I have voiced my concerns about this cultivar in terms of nut quality and scab susceptibility. This past winter, we were able to look at Mandan nut samples grown in three northern pecan states (photo at right).

    Results from of last winter's nut evaluations for Mandan are given in the table at right. When I compared the numbers in the table with the photo above I was surprised to find that the large Missouri nut had the lightest nut weight. It seems that Mandan nuts have such a thin shell that total average nut weight is largely determined by how well a Mandan tree can fill kernel (look at the differences in % kernel).

   Mandan produces a kernel with some serious defects. The Mandan sample from Kansas produced the best kernels of the three samples evaluated (photo at right). Looking carefully at these pecan kernels I find five problems.
  1. The dorsal groves are narrow and deep and can often trap inner-shell material.
  2. Every kernel produced a dark colored flap of seed coat at the end of the kernel (marked A).
  3. The kernel has prominent dark veins (marked B).
  4. The surface of the kernel is wrinkled, giving the nut meat a shriveled appearance (marked C).
  5. A dark spot often appears on the underside of the kernel (marked D) that is not insect related.

    The Missouri Mandan tree suffered from an extended dry period during mid-summer, giving us the opportunity to see how kernel quality is impacted by drought. Dry weather caused the Mandan kernel to be smaller, more wrinkled, and darker in color (photo at left). What is hard to see in the photo is the fact that the underside of the Missouri Mandan kernel is deeply depressed due to poor kernel fill.
    If you are interested in producing quality pecan kernels, I would avoid grafting Mandan into your orchard.

Tuesday, June 2, 2015

Pecans don't grow true from seed

    Over 30 years ago, we planted Giles seedlings in our pecan grove to help fill in the gaps that existed among much larger native pecan trees.  Since that time, the trees have grown and matured into nut bearing trees. In the photo above, I have outlined a pair of Giles nuts. The rest of the nuts in the photo were harvested from the Giles seedlings. Note that not one of the nuts produced by the seedlings looked exactly like a Giles nut.
    The Giles seed we used for these trees dates back to the 1980's and originated from our field trials at that time. Since pecan is a wind pollinated crop, the pollen parent for these seedling trees could have been anything from a native tree to a large improved cultivar such as Mohawk or Maramec. Its obvious from the photo above that some of the seedling trees received  some "large nut" genes from the pollen parent.

     The table at left provides some additional data on these Giles seedlings. For the 2014 crop year, our Giles nuts averaged 6.36 g/nut and 52.66% kernel. All but one of the seedlings produced nuts that were smaller than the parent tree. Only four seedling trees produced nuts that had higher percent kernel than the Giles parent.
    Of all of the seedling trees, KS800 has consistently produced nuts with outstanding kernel quality and appearance. However, this tree has 2 negative traits. It has an upright growth form that produces numerous narrow angled branch connections. But more importantly, the tree is a light nut producer.

     The moral of this story is that it is very difficult to find outstanding new pecan cultivars by just growing out some open-pollinated seed. We planted these trees in our native grove knowing full well that we wouldn't discover a new "super Giles" tree. We did, however, establish some new trees in our native grove that preserved the genetic diversity of our tree stand while improving the average percent kernel of our native crop (natives average 45% kernel, the Giles seedlings averaged 50.64% kernel).