Friday, July 1, 2016

Be careful when pulling off stalked buds

    Yesterday, I spent the morning trimming grafts and training the scion to a nice central leader.  Just two weeks ago, I worked on these same trees selecting a single scion shoot and removing stalked buds. However, it is amazing how fast bark grafts can grow. Many grafts had grown 10 to 12 inches taller in just two weeks. Along with the new growth, the tree also developed new stalked buds (red arrows point to stalked buds in photo at right). My first step in training these grafts is to remove all stalked buds. Next, I used flagging tape to tie the new growth to the bamboo stake I already had in place.

    When I remove stalked buds I always start at the top of the scion shoot and work my way down. At some point, I will come the location on the shoot were I had removed stalked buds previously (2 weeks ago in this case). You need to watch carefully as you tear off the stalked buds. In the photo at left, the red arrow points to a stalked bud that has developed since the last time I removed stalked buds. This bud will be removed.
    The yellow arrow points to a brown scar on the stem indicating the position of a stalked bud that I removed 2 weeks ago. Below the scar is a secondary bud that is starting to grow. I will leave this bud in place to form a wide angled lateral branch. Remember, by the time a secondary bud starts to break, it will be located well below the central leader and in perfect position for lateral branch formation.

Wednesday, June 29, 2016

Don't let pecan trees get top heavy

   Earlier this year, I showed you how to use directive pruning to prevent a tree from developing a bushy, leaderless top. The photo at right is a great example of what can happen when a bushy, multi-stem top is allowed to grow unchecked.  After the foliage of this tree was soaked by a recent rainstorm, the added weight of water on the foliage was enough to bend the tree down to the ground. Fortunately, the main trunk did not break but this tree needed my immediate attention.
  Since the top of the tree was so close to the ground, I took a quick photo of the tree's apex (photo at left). I count five new shoots growing out of the top of last year's wood. With all that new growth at the very top of the tree, it is no wonder the tree became top-heavy during a rain storm.

    Fixing this tree was a two step process. First, I pruned the top of the tree. I selected one shoot to be the central leader then employed the 2-foot rule to prune the rest of the tree. I did all this pruning while the tree was still bent over on the ground (no need for a ladder!). The second step was to install a ten foot tall tree training stake to hold the tree upright. I attached the stake to the base of the trunk using some white electrical tape (white? its just what I had on hand). Next, I lifted the tree up and used additional wraps of tape to hold the tree in place against the wooden stake (photo at right). As this tree increases in diameter over the summer, it should gain enough wood strength to hold itself up without the wooden stake.

Tuesday, June 28, 2016

Monitoring pecan scab and making the decision to spray

     Last week I scouted the pecan grove for pecan scab. For the most part, our trees look pretty clean. I had a hard time finding scab lesions on any part of this year's new growth. However, when I walked over to trees of some extremely scab-susceptible cultivars, new scab lesions were present on some of the foliage (photo above). Dooley, Hirschi, and Maramec were covered with scab last year but this year, with a drier than normal month of June, scab lesions were confined to only certain leaves and on the upper leaflets of those leaves. This kind of uneven distribution of scab lesions on foliage can be explained by the simple fact that the scab fungus prefers to attack rapidly expanding new plant tissue. For a short period during the leaf expansion phase of spring growth, weather conditions became perfect for the release of pecan scab spores. When those spores landed on leaflets that were still expanding, they were able to infect the new tissue and create a fresh scab lesion. 

   When most growers think about pecan scab, a mental picture of blackened pecan shucks and small pecans comes to mind. However, scab can cause major problems with the foliage. Scab lesions can form on the rachis of the leaf and effectively cut off water and nutrient supplies to a leaflet. In the photo at right, The terminal leaflet of one leaf has fallen off due to scab while on the other leaf several leaflet have dried up and dropped off the rachis.
     Under growing conditions in SE Kansas, foliar scab is primarily a problem on severely susceptible pecan cultivars (Dooley, Hirschi, and Maramec).  Scab is so bad on these cultivars, I've begun the process of eliminating these cultivars from our grove.  

   The main reason for scouting for scab last week was to see if the fungicide we applied with our casebearer spray was effective for keeping scab lesions from forming on nuts. The photo at left shows a cluster of Dooley nuts. As of last week, small scab lesions had formed of leaves, leaf rachii, and the pedicle of the nut cluster. The nuts remained free of scab.
   On Monday, June 27th, we received an inch of rain from two separate rain showers (early morning and late afternoon). Our temperatures have remained warm in spite of the rain and the increased humidity has made ideal conditions for the spread of scab.

    Today, the day after the rain showers,  we started up the sprayer first thing in the morning to apply a fungicide to our trees (photo above). Since it looked like we had a short window of opportunity to spray this week (additional showers are forecast for Thursday, June 30th thru Sunday July 3rd), it was very important to get a systemic fungicide on our pecan trees to protect our crop. We applied Quilt Xcel at the rate of 19 oz/acre.

Thursday, June 23, 2016

Galls on seedling pecan trees

   I was trimming up some young trees when I came across a seedling tree that had leaves sprinkled with light green galls (photo at right). These galls are formed by the plant in response to the feeding of an insect called the pecan leaf phylloxera. I find leaf phylloxera most commonly on juvenile pecan trees that have not yet been grafted.

    I photographed a couple of leaf phylloxera galls on the upper side of the leaf blade then flipped the leaflet over so you can see the same galls from the under side (photo at left). On the upper leaf surface the galls a raised, irregular-shaped and smooth. On the lower side of the leaf, the galls are raised with a nipple-like projection in the center of the gall.  
     I cut open one of the galls, then photographed both halves (photo at right). The gall was filled with aphid-like insects. I found both winged adults, and wingless nymphs inside the gall. These small insects feed on pecan plant tissues that make up wall of the gall.

  Eventually the gall splits open on the underside of the leaf allowing winged adults to leave the gall (photo at left). After winged adults mate,  female phylloxerans will find a secluded spot in the rough bark of the tree to over winter.
   I usually don't bother trying to control these insects on juvenile pecan trees. Once I graft the tree, the problem seems to disappear.