Friday, May 30, 2014

Checking last year's grafts

     Last winter was rough on new grafts. Like area many growers, I've discovered that some grafts made in 2013 were  completely dead all the way down below the graft union. Other grafts looked perfectly OK and were sprouting new shoots. The most interesting part of part about graft winter kill this year is that it had nothing to do with choice of scion cultivar.  In fact, I can find no logical reason why some grafts died over the winter whiles other thrived.
    The photo above shows two Kanza grafts made in the same field just 100 feet apart. The graft on the left is completely dead. You can see where I had tied the graft's new growth to a bamboo stake with blue fagging tape last summer. Now, the tree is pushing out trunk sprouts below the graft union in an effort to grow a new top. Note the reddish color of the foliage. This tells me that all new shoots are coming from the seedling rootstock. I'll let this tree grow out this year and place another Kanza scion on the tree in 2015.
   The healthy tree (above, right) has already developed numerous new Kanza shoots. The only problem is that this tree has developed a 'lolly-pop' appearance--all the new shoots are clustered at the top of last summers new growth. This growth pattern is common for open grown pecan trees and is one of the major causes of poor tree structure. During this time of year I like to practice a little directive pruning and follow the 2-foot rule for tree training.

    The photo at right shows before and after views of the upper portion of last year's healthy graft.  There were at least eight new shoots growing to form the 'lolly-pop' at the top of this tree. My first priority was to identify the one vigorous shoot that would become my central leader. Next I removed all other lateral shoots within 2 feet of the top of my chosen leader.  This left me with a couple of lateral shoots at the base of the 'lolly-pop'. I then pinched out the growing points of the two lateral branches to slow their growth and help focus more  of the tree's energy on the central leader.
    Pruning out most of the 'lolly-pop' will also help stimulate growth from lateral buds further down the stem. In a couple of weeks, I should see buds breaking all along the trunk in areas that currently look bare. In training a young tree, my aim is to develop a well balanced tree with lateral branches growing out at regular intervals all along the trunk.   

Wednesday, May 28, 2014

Pecan grafts breaking bud

   Its been about 3 weeks since I grafted pecan trees in my orchard. Look carefully at the photo at right and you'll notice that the buds on the scion have broken and are about one-inch green. Below the graft union is a profusion of trunk sprouts, producing leaves with the characteristically red tinge of a seedling rootstock. You should also note how the trunk sprouts got a head start on the scion sprouts in terms of growth.  When I applied the graft, buds on the scion were fully dormant. In contrast, buds on the trunk had already acclimated to spring time temperatures and were primed to go as soon I cut the top and placed the graft.
   To focus all the tree's energy into growing the buds on the scion, I pruned all the trunk sprouts off this tree. I like to complete this simple task as soon as I see new growth on the scion.  I have seen cases where trunk sprouts were not pruned off during the first summer after grafting and those sprouts eventually out-grew and shaded-out the scion. Lost in the deep shade of trunk suckers, a sprouted scion will actually die from lack of sunlight.
   The lesson here is to check your grafts early and often. And don't forget to always carry a pair of pruning shears.
    The photo at right shows a little larger tree with another graft I made this spring. The graft has sprouted but the side limbs I left below the graft have grown even faster. I left these lowers limbs on the tree to provide leaf area to support the root system but you can already see that these side shoots have turned to grow upwards and are competing with the graft for sunlight. I don't want to remove all the leaves below the graft union but I need to slow down the growth of these lower limbs. 
   The photo at right shows the same tree after I made several pruning cuts. First, I pruned off all but two branches below the graft. Second, I  removed all upward growing shoots from those two branches. And finally, I pinched back the terminals of edge side branch making sure to prune to an outward growing bud. Now my graft is back in full sun and ready to take off. I'll be back in a couple of weeks with some plastic tape to tie the scion's new growth to my bird perch. Oh, how I would hate to see a successful graft blow out in the wind!

Tuesday, May 27, 2014

Winter kill of pecan trees

    Although the winter of 2013-2014 didn't set any records for low temperatures in our area, we did drop down to cold enough temperatures to cause some obvious winter kill. The photo at right shows two Shoshoni trees. The tree on the left has leaved out normally while the tree on the right has only few new shoots growing  on the lower trunk and a few low branches (see close up photo below). This mostly dead Shoshoni tree is a perfect example of an alternate-bearing cultivar that lost winter cold-hardiness following an "on" crop year. A heavy crop pulls massive amounts of plant nutrients out of tree stems in an effort to fill nut kernel. The following winter, depleted branches are less able to withstand cold winter temperatures. Following a heavy crop, cold damage can occur even at moderately cold temperatures (<-10 F).
   The photo at left shows the few green shoots produced by our heavily damaged Shoshoni tree. With the massive amounts of limb loss sustained by this tree it would take 5-7 years for this tree to recover its canopy. In the past, Shoshoni has proven to be a difficult cultivar to manage and trying to help this tree recover is probably not worth the effort. We'll be making only one more pruning cut on this tree--at ground level!

    I've seen one other type of cold injury this Spring. Again the damage occurred on the cultivar, Shoshoni, but this time the damage is not crop load related. The photo at right shows a Shoshoni tree with several large limbs killed by winter cold. It wasn't until I closely inspected the structure of this tree that I discover why only a portion of the tree's canopy was killed during the winter.

 The photo at left reveals that this Shoshoni tree suffered major limb loss during the ice storm of December 2007. Broken limbs were pruned off leaving large branch stubs. New shoots then sprouted out from these branch stubs and grew at an extremely rapid rate. Rapidly growing shoots remain active and full of sap late into the fall. This delay in the normal hardening-off process before the start of winter only leads to a reduction in cold hardiness. The side of this Shoshoni tree that did not break in the ice storm, suffered no winter injury.
  We will be pruning the dead limbs out of this tree. After pruning, this tree will have enough canopy left to support a partial nut crop this fall.

Thursday, May 22, 2014

Another sawfly species appears

  As this year's dry spring weather continues, another species of sawfly larvae has appeared in our pecan grove. Megaxyela major produces a yellow larvae with black head and a row of black spots on each body segment (photo at right). These sawfly larvae chew large holes in the foliage and can usually be found curled around leaves, rachises, or leaf midribs.
    Like the sawfly species I described in early May, this species of sawfly has a single generation per year. Fortunately, I have never seen M. major populations so large as they require a pesticide application. The cluster of sawfly larvae pictured at left occurred on a single pecan branch terminal. It has been the only colony of his species of sawfly we have found across our entire 80 acre pecan  grove.

Wednesday, May 21, 2014

Pheromone traps for monitoring pecan nut casebearer

   We use a rope and pulley system to install pecan nut casebearer traps up into the canopy of our pecan trees (photo at right). Since these insects spend their entire life cycle in pecan trees, we need to place the traps in a location where casebearers are flying. Male casebearer moths enter our traps when they detect the female sex pheromone being released from a small rubber septum placed inside the trap. The moth then gets stuck in the sticky goo spread on the inside floor of the trap (see photo below).
    We usually capture our first male moths during the middle of the pollination season and we found one moth last night. In the photo at left, the casebearer moth is pointed out by a red arrow. This arrow also points to the ridge of scales on the wings that helps to identify this small, gray moth as a pecan nut casebearer. You can also see the grey rubber septum that emits the female sex pheromone.  The rubber septum is roughly 3/4 inch in length and the casebearer moth is 3/8 inch long.

Thursday, May 15, 2014

Controlling weeds around young pecan trees

   During most years, regular spring rains and muddy soil conditions keeps us out of the field at this time of year. In fact, the vast majority of floods that occur on the Neosho River happen during the months of May and June. However, a drier than normal Spring has enabled us to get an early jump on weed control this year. During periods of calm winds, we use a 30-gallon, electric sprayer to apply roundup in a seven foot circle around each tree (photo at right).
   Roundup (gyphosate) is a systemic, contact herbicide that can damage pecan trees if spray droplets contact any green tissue. To limit possible spray drift problems, we use a hand held spray wand and adjust the nozzle to a course spray pattern (large droplet size). We use a generic form of roundup at the rate of 2 oz. per gallon. To help the roundup penetrate weed leaves, we add liquid ammonium sulfate and a non-ionic surfactant to the spray tank.

    What you don't see in the photo above is the fact that we walk through the orchard a week before spraying and trim off any basal sprouts or any new shoots sprouting from the lower portion of the trunk. One of the most common causes of roundup injury to young pecans is accidentally hitting unseen basal sprouts hidden in tall weeds.
    During this preliminary walk through the orchard, we discovered several trees that were killed back to the ground by mid-winter cold. In the photo at left, you can see we had two years of strong growth on this young graft but the entire tree died back to the ground line following last winter's intense cold.  However, all is not lost. This tree has already developed a couple of basal sprouts that will provide a new place to graft in the future.
    In the mean time, we were fortunate to discover these new shoots before applying our herbicide spray. First, we pulled the weeds away from the stump sprouts by hand. Then, we very carefully sprayed the rest of the area around the tree. Roundup can penetrate both the leaves and green bark of tender pecan shoots, so be very careful.

Monday, May 12, 2014

Flowering after a late Spring frost

   On the morning of April 15th, temperatures dropped to the mid 20's (F) freezing back all emerging pecan buds. The photo at right shows the impact the freeze had on Greenriver shoots by late afternoon that same day. The dark olive green color of the new growth indicates total freeze kill.  At the time of the freeze, Greenriver was one of the earliest budding pecan cultivars in our cultivar collection.
   A couple of weeks later, I went back to our Greenriver trees and found some signs of new growth amongst all the frost killed buds (photo at left). The question at that time was-- "Will our Greenriver trees have enough energy to produce pistillate flowers?".  I wasn't too worried about the production of catkins on frost damaged trees because I could already see catkins being produced adjacent to the new green shoots (visible in photo).
   Today, I took a ride in our hydraulic lift to check for Greenriver pistillate flower production.  The photo below is a common example of what I found. The tips of last year's growth were largely barren except for the remains of frost damaged buds. Buds at the base of last-year's-wood produced both new catkins (red arrow) and a strong vegetative shoots. On the end of many of these vegetative shoots I found pistillate flowers (inside red circle). So it looks like we are still going to have a decent pecan crop despite the April 15th freeze.
    I am convinced that our regular, twice-per-year, fertilizer program is largely responsible for our trees having the energy to produce pistillate flowers on shoots developing from basal buds.

Friday, May 9, 2014

Dry Spring weather promotes sawfly populations

   Today, we were out working in the pecan grove when we spotted evidence of sawfly larvae feeding on pecan foliage. It is easy to spot. Just look up into a pecan tree's canopy and if you see leaves with a series of holes chewed into leaf blades, you can bet you have had sawfly larvae feasting on this year's new growth (photo at right).

   To find out if you have a active population of feeding sawflies, look on the underside of the foliage. You should find a small green worm chewing holes in the foliage (photo at left).
At this point we are not seeing enough larvae to justify a pesticide application but we need to watch our orchard  carefully over the next week or so to make sure we don't get surprised by a major outbreak of this insect.
   Sawflies are not actually flies at all. The larvae we see eating pecan foliage are actually the juvenile form of a member of the wasp family known by the scientific name, Periclista marginicollis. Although the larvae pictured at right looks like a caterpillar, note that this worm has 3 sets of true legs near the head followed by pair of prolegs on every body segment thereafter. Caterpillars or the larvae of butterflies and moths also have prolegs but not on every body segment behind the true legs.
    Sawflies adults emerge in the spring and produce a single generation per year. When larvae fully mature, they drop to the ground and pupate in the soil. I have always found that dry spring weather conditions seem to promote sawfly populations.

Wednesday, May 7, 2014

Checking pecan cultivars for flowering habit

Mullahy, 5 May 2014
   As our pecan trees bud out and start to develop catkins, I've been checking out the flowering habits of several cultivars. In a previous post, I showed you how to tell if a pecan cultivar is protandrous (early pollen shedding) or protogynous (late pollen shedding) just by looking at the shape of emerging catkins. Earlier this week I photographed the catkins of several pecan cultivars so I could determine their flowering habit.
    The photo at right is a Mullahy terminal. Note that the catkins are long and thin, which tells me that Mullahy is a protogynous cultivar and will shed pollen late in the pollination season.

Hark, 5 May 2014
   The photo at left shows a Hark shoot. Hark catkins are short and fat indicating that this cultivar has a protandrous flowering habit. Hark will release its pollen early during the pollination season.
   In the photos below you should be able to see that the shape of the catkins indicate that Warren 346 and USDA 61-1-X are protandrous cultivars while City Park is a protogynous cultivar. It is interesting to note that the catkins of City Park are still elongating at the time this photo was taken and have not yet achieved their full length. It looks like City Park will be shedding its pollen at the tail end of the pollination season.

Warren 346, 5 May 2014
USDA 61-1-X, 5 May 2014
City Park, 5 May 2014