Wednesday, August 16, 2017

Marking successful grafts

     By the first part of August, scions I grafted last spring using a bark graft have grown 5 feet in height (photo at right). Over the summer months I've pruned the scion down to one shoot, trimmed off trunk sprouts, and removed grafting tape to prevent girdling. Now its time to remove all graft wraps and paint the graft union to make field identification of successful grafts easy.
   At this point in the growing season, my bark grafts are still covered with aluminum foil and a plastic bag. To remove these wraps I take my knife and make a vertical cut through plastic, foil, and grafting tape. After making the cut, I simply peel off all the graft wraps together at one time.

   Once uncovered, you can see how moist the tree is under the wraps (photo at right). By mid August, the graft union is fully formed and is beginning to slow its growth rate.  The reason I like to unwrap the grafts at this time is because ants and dogwood borers like to make a home in the moist environment under the wraps. Since both insects can damage tree cambial growth, exposing the graft union to the air helps prevent this kind of insect damage.

   Unfortunately unwrapping a graft union in mid summer can cause sun burn to recently exposed bark and cambial tissues. I use latex house paint to prevent sun scald and to mark successful grafts (photo at left).

    One advantage of painting the graft union is that I can now easily see which trees have been successfully grafted from a distance (photo at right). I also use different color paints to identify the cultivar grafted. On my farm, Kanza trees are white, Lakota yellow, Hark green, and USDA 61-1-X is red. Once painted, I don't need to worry about missing ID tags or trying to draw an accurate map of an orchard created from a field of randomly spaced volunteer pecan seedlings.

    We are rapidly approaching the season of the year when buck deer begin rubbing young trees. So after marking my new graft with paint, I replace the deer cage over the tree to protect this fine young Kanza graft (photo at left).

Monday, August 14, 2017

Crop load management

   This year, several of our pecan cultivars have set an over-abundance of nuts. So many nuts in fact that the tree couldn't possibly fill all those kernels and nut quality would suffer. So, I've been cutting nuts to determine when pecans enter the water stage (photo above) and when it's the right time to shake trees to reduce the crop load.  Today, with the nuts at the right stage and the sun shinning we used our tree shaker to remove a portion of our crop.

Lakota before nut thinning
   The cultivars in our orchard that required nut thinning this year were Pawnee, Gardner, Faith, Lakota, and Osage. Even some of the trees in our Kanza block needed crop load reduction. We used a Savage PTO shaker equipped with doughnut pads to give each tree a light shake. When the nuts are at full water stage, it only takes a short burst of vibration to rain down green nuts.  

Lakota after nut thinning
    Summer shaking is not an exact science but once you become accustomed to the practice you get a feel for the technique. During shaking you can actually see heavily laden limbs spring back upwards as the weight of nuts is reduced. Look closely at the before and after photos of shaking a Lakota tree, you can see the limbs have moved upwards.

   The one thing you can't do is look at the ground. Seeing hundreds of green nuts on the ground can make you feel like you've just thrown away a good portion of your crop (photo at left). But just remember, the remaining nuts on the tree can now fully pack kernel inside the shell resulting in a yield equal to or greater than if the tree was never shook. In addition, better quality nuts will command a better price and the tree will return with a good crop next year.
    One advantage to shaking for crop load regulation is that you can always skip over trees that are not overloaded. This year we shook about 80% of our Pawnee trees and 15% of our Kanza trees.

   The greatest danger it using a trunk shaker in mid summer is the risk of bark damage (photo at right). Clamp on the shaker improperly or not tight enough and you can tear off bark. This causes lasting tree damage that is hard to reverse. My advice is to not get in a hurry, and clamp on and off the tree with great care.

Thursday, August 10, 2017

Pecan leafminers

   Have you every noticed a brown spot on the upper side of a pecan leaflet (photo at right)?  What looks like a foliar disease is actually the home of a small caterpillar. The upper-surface blotch leafminer (Cameraria caryaefoliella) feeds on leaf cells just under the epidermis of the leaf and creates an irregular shaped  brown blotch. Look carefully at the blotch and you'll see that under the papery thin epidermis you'll find a pile of black frass left by the caterpillar.

     I carefully pealed back the upper layer of the blotch to see if I could locate the caterpillar underneath (photo at left). I found the worm and moved him out to the leaf surface. The larva was black in color and very sluggish. The color and behavior of this caterpillar indicated that this poor fellow has been parasitized by a miniature wasp. That's one leafminer that won't be metamorphosing into a adult moth.
   Less common in my orchard is the pecan serpentine leafminer, Stigmella junglandofoliella (photo at right). This leafminer also feeds on leaf tissue just under the epidermis of pecan leaves but creates a meandering tunnel. As the larvae grows in size, the tunnel becomes wider making it look like a small snake is sitting in the surface of the leaf. Eventually the larvae in the tunnel will pupate and a small moth will emerge for the widest portion of the tunnel.

    Leaf miners are typically a non-economic pest. I commonly find them on young trees that receive little or no insecticide treatments. Once trees start bearing nuts and are regularly treated for major nut feeding pests, leaf miners largely disappear from the orchard.

Tuesday, August 8, 2017

Kernel development: 8 Aug 17

   This time of year I like to monitor pecan kernel development pretty closely for two reasons. The first is to determine when nuts reach the full water stage which is the optimum time for shaking trees to reduce an excessive nut crop. Then when kernels transition into the dough stage, I'll know when pecan weevils will begin laying eggs inside the nut.

   Today, I cut open the nuts of several well known pecan cultivars and a few new and emerging cultivars (photos at right and below). Let see how their kernels are developing.
   The first set of cultivars I placed in a photo together are the progeny of Major.
Kanza, Lakota, and Hark all dripped out liquid endosperm when cut open but the kernels inside have not yet reach the full water stage.

    In the second photo, I placed three early ripening cultivars to see if one of these pecans had reached the full water stage. Osage and Goosepond are close but only Mullahy has reached what I call the water stage. Notice how the kernel halves of Mullahy have grown almost all the way to the base of the shell.
     The next photo shows a collection of USDA cultivars. I've arranged the nuts in this photo by ripening date--Pawnee being the earliest to ripen and Mohawk being the latest. I was surprised to see that Pawnee was still only three quarters of the way to full water stage. Kanza and Lakota were both ahead of Pawnee this year. I guess that why I still need to check kernel development every year.

   The final photo show a couple of old time cultivars (Giles and Posey) versus two recently discovered cultivars (SWB617 and Waccamaw). SWB617 is a seedling of Giles but it ripens way before it's parent. As you can see SWB617 has nearly achieved full water stage while Giles is still at one half water. Waccamaw is a large nut similar to Posey and their stage of kernel development is close to the same. I'll be interested to see what Waccamaw does in the future.

Monday, August 7, 2017

Spraying for weevil, stinkbug, and scab

    We had a good rain shower over the weekend which came at a perfect time to promote nut growth and kernel fill. But 1.5 inches rainfall also provided plenty of moisture to softened the soil and allow pecan weevil to start emerging. So today we fired up the sprayer (photo at right).
   Today's pesticide application was aimed at controlling three key pests; Pecan weevil, stinkbugs, and pecan scab.  We generally spray the grove in early August for stinkbug control but the wet weather dictated that we also control weevil and scab. We used Warrior 2 for insect control and Quilt Xcel for disease control.   
    Applying a fungicide this late in the season has proven beneficial during wet summers to control not only pecan scab but also pecan anthracnose and downy spot. Judging from the forecast we are in for a cool wet August.

Thursday, August 3, 2017

Pecan development and summer shaking

    Many orchards in northern pecan states are blessed with excellent pecan crops this year. Some cultivars have even set excessive crop loads increasing the likelihood of poor kernel quality this fall and  increased risk of cold injury this winter. Using a trunk shaker to remove a portion of the crop in mid summer is the best way to avoid kernel quality issues this year and increase return bloom next year.  However, for summer trunk shaking to be effective growers must time their nut thinning operations by carefully monitoring nut development.
    Trunk shaking to thin the crop works best when pecans have reached full size and the kernel is in the water stage. This means that growers must monitor their crop to check on kernel development. Yesterday, I collected nuts from four pecan cultivars (photo above). Let's see what inside.

    To check kernel development, hold the nut so you can see the attachment scar on the bottom of the nut (photo at left). Note that the attachment scar is oval in shape. The long axis of the oval was aligned with the stem of the pecan shoot.
   To reveal both sides of the kernel and the progress of kernel development, I cut the nut in half perpendicular to the long axil of the oval attachment scar (photo at left). If you find the mid point perfectly, your knife will split the shell on the suture. 

      The nuts I cut open yesterday, revealed that kernels have not yet reached full water stage (photo at left). Currently, Pawnee is at 1/2 water stage and Giles 1/4 water stage.  Nut development can move quickly at this time of year so be prepared to monitor nuts about every 5 days or so. From past experience, we have thinned Pawnee about a week before Kanza and about 10 days before Giles and Lakota.

Monday, July 24, 2017

Monitoring scab

Native pecan infected by scab
     The 2017 growing season started off with ample rainfall and ideal conditions for the spread of pecan scab (photo at right). In response, we have made two fungicide applications this summer (Mid-June and early July). However, the weather in our area has turned off hot and dry and the spread of the disease has slowed dramatically.
     We got a late start in spraying for scab this year because I kept waiting for pecan nut casebearer to appear (it never did) before making a trip through the orchard with my sprayer. As a consequence, we have a light scab infestation on susceptible cultivars.

   In looking at several cultivars, I found that most scab susceptible cultivars have a non-damaging levels of scab on the shucks. The Giles nut cluster pictured at left is a good example of how our less that perfect scab control efforts have held disease spread to a minimum.


    Of course, a scab free cultivar like Kanza looks perfect at this time of year (photo at right). However, it is worth mentioning that Kanza does benefit from receiving fungicide applications. Kanza may be resistant to scab but it is susceptible to pecan anthracnose which can cause fungal leaf scorch and shuck rot.

    I also looked at Mandan to confirm my assertion that this fairly new pecan cultivar is susceptible to scab (photo at left). It appears that Mandan is not super-susceptible to scab but will definitely require a fungicide program to ensure top yields.

Tuesday, July 18, 2017

Pecan nuts rapidly expanding

    July is the month that you can finally look up into a pecan tree and notice nuts hanging from branch terminals. At this point during the growing season, pecans have entered their rapid growth phase, when nuts grow in size and the kernel tissues begin forming.  Pictured at right are some nuts I harvested today from four cultivars. I chose these cultivars because they range in nut maturity date from very early (Osage) to late (Maramec). At this point in the season, the nuts of all 4 cultivars are roughly the same size but slicing open each nut shows that the progress of kernel development differs. While the nut is expanding, the kernel inside is composed of the seed coat and liquid endosperm (looks like water).
    At the start of nut enlargement,  the seed inside the nut is small and heart shaped (like the Maramec nut pictured above). As the kernel expands, the seed coat expands downward towards the base of the nut and you can see two kernel halves start to develop (Osage nut above). Cutting nuts open at this time of year can give you a pretty good idea when nuts will ripen in the Fall (at least in comparison to other pecan cultivars). In the photo above, I've arranged the four cultivars in order of ripening. Osage ripens earliest, followed by Kanza, then Greenriver, and finally Maramec.

   While I was out collecting nut samples,  I decided to pull some nuts from 3 cultivars that are relatively new to our cultivar collection (photo at right). Judging from the size and shape of the kernels, Hark and Yates 68 should ripen about the same time as Kanza. The kernel development of Surecrop looks to be closer to Greenriver.
   We may be suffering through the dog days of summer, but cutting open pecans in mid-July only makes me optimistic for a good pecan crop this fall.

Monday, July 10, 2017

Japanese beetles feast on young pecan trees

    People living along the east coast of the United States have become all too familiar with voracious Japanese beetles chewing the leaves of  trees, shrubs, and garden plants. This introduced pest was first found in Riverton, NJ in 1916 and has slowly spread across the eastern US moving just a few miles each year. This year we've spotted quite a few clusters of Japanese beetles feeding on pecan leaves in Cherokee Co. KS (home of the Pecan Experiment Field).
    The Japanese beetle spends most of the year as a C-shaped grub-worm feeding in the soil on the roots of ground cover plants. Adults start emerging in mid-June and aggregate in large numbers on a single plant. The adults feed on over 300 species of plants including pecans. The beetles feed on leaf tissue but only remove tissue between leaf veins. This feeding behavior results in leaves with a skeletonized appearance (photo above).
   Adult beetles have bright metallic coloration. The head and thorax are metallic green while the wing covers are copper colored (photo above). Upon emerging from the soil, adults release a strong pheromone that attracts other adults to the same location on the tree. Once aggregated, they feed on leaf tissue then shorty thereafter begin mating. Mated females will then drop to the ground to lay 30-40 eggs in the turf.  Adult Japanese beetles are present for about a month's time, starting in mid-June and continuing until early July.
    In our pecan orchard we have found Japanese beetles only on trees that did not receive the insecticide treatment we made in mid-June.     

Thursday, July 6, 2017

Unwrapping a 3-flap graft

    The July 4th Holiday weekend was a great time to work on all 3-flap grafts I made this past spring. A month ago I had visited all newly grafted trees to remove stump sprouts. This time I am going to train the tree to a single shoot growing from the scion and re-wrap the 3-flap graft union.
   Since I last visited the tree pictured at right, new trunk sprouts have grown and the scion has developed a nice strong shoot. I grabbed my grafting box and started right to work. 

    My first job was to trim off all trunk sprouts that had developed below the graft union (photo at left). Hopefully, as the new scion grows in height and diameter, the tree will be less prone to sprouting new trunk shoots in the future.

    Next, I proceeded to remove all the wraps placed over the graft union back when I originally grafted the tree. When I make a 3-flap graft, I bind the graft union tightly with grafting tape. To allow the graft union to freely increase in diameter as the tree grows this summer, I need to remove that tape.
    The simplest method to remove the wraps from the graft is to use a sharp knife to cut the tape, aluminum foil and plastic bag with a single vertical slice (photo above, right).

    Once cut, I peel back the layers of graft wraps and remove them from the tree (photo at left). At this point, the graft has callused over but the union is still weak and can easily be broken. When pulling off the wraps, I'm always careful not to pull and tug  the graft union itself.

      Once I remove the graft wraps, I can see white callus tissue growing between the bark flaps (photo at right). Since this new tissue developed and grew in the dark under the original graft wraps, it is very susceptible sun-scald.  So, to prevent sun injury during the heat of the summer, I will re-wrap the graft union in aluminum foil.

    Just like covering the graft the first time, I rip off a piece of foil and place it over the graft union. This time there is no grafting tape underneath. The foil acts as a sun block protecting the tender callus tissue from damage.

    To make sure the foil doesn't get blown off the tree in the wind, I tie a piece of grafting tape around the foil. Once I'm done with the graft union, I turn my attention to other parts of the tree.

    The photo above shows a before and after view of pruning the scion. I want all the tree's energy focused on the one, strong shoot growing from the upper bud of the original scionwood stick. I prune off the lower bud (red arrow) and then remove the stub at the top of the scion (yellow arrow). Removing the stub isn't totally necessary but it will help the tree grow over the wound much cleaner and faster. 

    Next I inspect the new shoot growing from the scion. If I see any stalked buds (yellow arrow), I pull them off.

    Finally I use some engineer's flagging tape, to tie the scion's new shoot to my bamboo training stick (photo at left). Before moving to the next tree, I'll replace the deer cage over this graft to prevent deer browse (deer cage can be seen in the background of this photo).
   I'll be back in 3-4 weeks to add additional ties to the new shoot and to trim off any unwanted new growth below the graft union.

Monday, July 3, 2017

Spraying for pecan scab...again!

    Its been 2 weeks since we made our last scab spray. Since that time its been hot and humid. Pecans are entering the period of rapid nut enlargement--a period when nuts are most susceptible to scab infection.  So between rain storms, we decided to start our second scab spray for the year (photo at right).
    We are using a systemic fungicide (Quilt Xcel) so, as long as we get 6 hours of drying time before the next rain, the fungicide should be effective.

Thursday, June 29, 2017

Time for pecan graft maintenance

    Today I was working on trimming and training this year's new grafts. The photo at right shows a young bark graft that has developed a nice strong shoot from the scion. However, this tree still needs some attention.
    Three weeks ago I forced new growth from the scion by pruning off all bark sprouts growing below the graft union. But now, you can see new bark sprouts have formed (note leaves with reddish coloration).
   So my first step in pruning this tree was to remove all stump sprouts (photo at left). Now, you can clearly see the graft union. My next step is to prune the scion's new growth down to one shoot.
    The photo at right is a close-up of the graft union. As you can see the scion has developed three shoots. The uppermost shoot (labeled A) is hardly sprouted out. I will remove this shoot by cutting the scion at the point marked by the red line. Next, I will remove the secondary shoot (labeled B) so that all the tree's energy will be directed to the much larger primary shoot that will become my new central leader.
    To prevent the grafting tape from girdling the scion, I'll remove the tape (labeled C) but leave the rest of the graft wraps on the tree at this time.

    After pruning the scion I'm left with a nice single stemmed tree (photo at left).  The slight crook in the stem will eventually disappear  as the new shoot grows in diameter. Before leaving this tree I always inspect the new shoot for the formation of stalked buds.
     I found  a stalked bud at nearly every leaf axil. In the photo at right, I pointed out all the stalked buds (orange arrows) on just a portion of the scion's new shoot.  Starting at the base of the shoot, I use my fingers to grab each stalked bud and pull them off the shoot. On this tree, I found stalked buds at every leaf axil over the entire length of the shoot.
Once the stalked buds were removed, I used some blue engineer's flagging tape (any color will work) to secure the new shoot growth to my bamboo training stick (photo at left). Now that I've pruned the scion down to one shoot, I want to do everything possible to prevent the wind from snapping off the graft. My final step in protecting this graft was to replace the deer cage back over the tree to prevent browsing damage.
   In about 3 weeks, this tree will need more attention. I'll need to prune off any new stump sprouts, remove stalked buds that develop on new growth and tie the new shoot to the stake as the tree grows in height.

Tuesday, June 27, 2017

Early signs of pecan scab infection

    We've had a fairly wet spring this year and along with the damp weather, pecan scab has made its early season appearance.  The photo at right shows a cluster of Giles nuts. Giles is a scab susceptible cultivar that must be protected with fungicide sprays in order to produce a harvestable crop.
   A quick look at the Giles nut cluster reveals just the smallest hint of scab infection, a very small black lesion on the upper left side nut. However, if you look at the leaf below the nut cluster you will numerous scab lesions appearing as black irregularly shaped spots.
   With plenty of scab spores up in the tree (coming from leaf lesions) we'll need a good fungicide program to protect the nut crop. We've sprayed once but additional sprays will be needed.

    On super scab-susceptible cultivars, like Hirschi,  the disease has already progressed to the nut crop. In the photo at left, a Hirschi nut (left nut) is already supporting a large scab lesion. You can also see scab lesions dotting the foliage. Historically we've had trouble controlling scab on Hirschi even with multiple fungicide applications. This year looks no different. Our Hirschi trees will receive the same spray schedule as the rest of the orchard but we'll probably lose most the nut crop from these tree due to scab.

Friday, June 23, 2017

What happened to my pecan tree's central leader?

    When I drove by my pecan grove the other day, I noticed a tree with a branch that had broken out in the wind (photo at right). At first glance , it looked like the central leader had snapped and I lost the top of the tree. So, I got out my 8 foot tall orchard ladder to take a closer look and the make some pruning cuts.
   Once I climbed up the ladder I could get a good look at the branch structure of this tree (photo at left). To my surprise the broken branch was not the central leader. What was once the central leader was bent over under the weight of an excessively bushy top.
     My first step in pruning up this tree was to remove the broken limb (photo at right). Next I needed to straighten up the leader (red arrow). At the same time, I needed to thin out the number of limbs that branched out from the trunk at nearly the same spot on the trunk. Rather than attach a training stick to the tree, I decided to use a lower branch (yellow arrow) to help retrain the tree. I chose this limb because it was leaning out in the opposite direction of the leader.
     I held both these limbs upright and taped them together using electrical tape (photo at left). I now had my leader pointing in the right direction. However,  I also had a training branch pointing in the same direction and in direct competition with the leader.

    I pruned off the top of the training branch just above the electrical tape (photo at right). This pruning cut immediately gave a sunlight advantage to the leader. However, the training branch would soon sprout new shoots so,  I decided to try a little old fashion trickery.
   At the base of the training branch, I girdled the branch (photo at left). I removed the bark from the branch from the point the branch attaches to the trunk upward for about 3 inches. Girdling a branch will not kill it immediately but will inhibit the movement of nutrients into the branch and seriously hamper shoot re-sprouting. However, the wood in the girdled branch will remain strong enough to provide support for the leader. After a year's time, the leader should gain in diameter and strength and  I can cut out the girdled branch completely.
   Next I turned my attention to the leader.  Each spring, a pecan tree will sprout 3 to 5 new branches from the terminal portion of last year's growth. This forms a growth pattern commonly known as a "crows foot". The photo at right shows that the leader of this tree grew a crows foot in both 2016 and 2017 (red circles). This growth pattern produced such a mass of foliage that the leader became top heavy and bend over from the weight.
    To make sure the leader would develop into a strong, upright-growing trunk, I needed to prune off all the side branches in this portion of the tree.

   In pruning the top of this tree, I removed both the 2016 and 2017 crow's feet (photo at left).  Suddenly, I've reclaimed a single central leader.

    Once I got through with redefining the top of the tree, I turned my attention to the side branches. I found that the lateral branches had sprouted so many new shoots this past spring that I needed to prune off some excessive leaf weight. I did that by first removing any new shoots sprouting straight upwards from a lateral limb. Next I headed back any new lateral shoot that had grown more than 2 feet in length.
    My biggest problem in making these pruning cuts is that I needed my 8 foot orchard ladder for every cut.  I guess that is the price I pay for grafting onto a fairly large rootstock tree and witnessing 5-7 feet of new growth each year. 

    It took me about 15 minutes to prune my tree with a broken branch. It seems most of my time was spent moving the ladder and climbing up and down. This fall (late Oct.) I'll prune out my training branch.