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.