Thursday, July 31, 2014

Canopy shape and tree spacing

    Back in 1995 we established a block of seedling trees that we later grafted to Kanza. The original tree spacing was  30 ft. x 30 ft. and  by 2012 the branches of some adjacent trees were starting to touch. In 2012, we developed a tree thinning plan that called for the removal of trees over several years starting in areas of the orchard that were showing signs of overcrowding. You can review this thinning plan and follow the history of tree removal in this orchard by viewing my post from last March.

     Today, I went out to our Kanza block to check on this year's crop load crop.  While walking through the orchard, I was struck by how different the tree canopies  looked between thinned and un-thinned areas. I took a couple of photos that I hope illustrate what I'm talking about.
    The photo at right shows the portion of our Kanza block that has not been thinned. The trees in the photo look really close together because I took the snapshot on the diagonal from the 30 ft. by 30 ft. tree rows. These trees are starting to touch and I'll need to thin trees from this area next winter. But what I really wanted you to see is the shape of each tree's canopy. Trees in the un-thinned area appear tall and columnar. The only pruning we do in this grove of trees is to remove low hanging branches or wind-broken limbs. So ultimately, the distinctive shape of these trees was determined by inter-tree competition for sunlight. To impact tree shape so dramatically, competition  for sunlight had to have started long before the branches of adjacent trees started to touch.

    So what happens when trees are thinned from the grove and sunlight streams down onto the sides of remaining trees.  The photo at right shows the portion of the Kanza block grove that was thinned in February of 2012. This photo was taken in the same diagonal direction as the photo of the un-thinned portion of the block. The trees in this area are now spaced 42 ft. x 42 ft.
    With only three years of new shoot growth, you can see how quickly the sides of these trees have grown out to take advantage of increased sunlight penetration into the orchard. Note how the tree canopies have changed shape to become more rounded. I'm also seeing more nut production on lower limbs in this portion of the orchard as compared to the un-thinned areas.
   This winter we will be cutting more trees out of this orchard according to our tree thinning plan. The number of trees we will remove in February of 2015 is yet to be determined but I keep you posted.

Monday, July 28, 2014

Pecan development: Rapid nut expansion


    Late July is the time of year when pecans are growing rapidly in size. With larger nut size, I can finally stand back, look at a tree and actually see the crop load held in the canopy. So this morning, I decided to collect some nut samples and check on kernel development.  In the photo above, the nuts I pulled from from five pecan cultivars are arranged by average date of nut maturity.  Pawnee and Gardner usually ripen in late September, Kanza ripens in early October, while Giles and Lakota ripen in mid October. By mid summer, a close look at nuts on the tree can give you a rough idea of when a cultivar will mature in the fall. Note that Pawnee, Gardner, and Kanza nuts are larger and plumper than the Giles and Lakota nuts. This tells me that kernel expansion is farther along in the bigger nuts and not as advanced within the smaller two cultivars.  

     I cut each nut in half to check my theory (photo above). Pawnee, Gardner, and Kanza had kernels that were about 1/4 expanded (Gardner looks less expanded but I missed the exact middle when slicing the nut open). Giles had the smallest amount of kernel and was actually just starting into the rapid growth phase of nut development. Lakota was further advanced than Giles but still behind the other three cultivars.
     All this discussion of nut development may seem like an academic exercise but we are rapidly approaching pecan weevil season.  Knowledge of nut development is critical for timing insecticide applications to control the pecan grower's number one enemy, the weevil. Pecan weevils can not lay eggs inside a pecan until kernel deposition begins. Early ripening cultivars will begin laying down solid kernel first and will be the most attractive to egg-laying female weevils. 

Thursday, July 24, 2014

Dogwood borers on young pecan trees

   Last weekend I was unwrapping bark grafts and I discovered a graft union covered by  a pile of nasty insect frass (photo at right). Looking closely at the grains of insect excrement, I found they were held together by fine silken threads. I pulled out my pocket knife to scrape off  all the debris when I discovered a cream-colored larvae with a red head.
    The larvae was a dogwood borer (Synanthedon scitula). This larvae definitely didn't like being out in the sunshine and immediately attempted to burrow down under the remaining frass piles (photo at left). Cleaning off all the frass, squashing the larva, and painting the graft union probably saved this graft union from being girdled by the dogwood borer.
    Once I found a dogwood borer in one of my grafts, I started to look at other trees for sign of borer activity. Dogwood borers feed on the inner bark and cambium of numerous hardwood trees and can become a serious pest in young pecan orchards. Adults are clear-winged moths that lay eggs on the bark of susceptible tree species. After hatching, young larvae search for a tree wound, branch attachment crevice, or graft union to enter the tree and star feeding on nutrient rich inner bark. The red arrow in the photo at right points to a column of reddish-brown frass pushed out of a dogwood borer's feeding gallery deep inside a branch attachment crevice. The frass pile usually takes on a tubular shape and is held together by fine, silken strands.

    I also found evidence of dogwood borer infestation on the trunks of young trees. the yellow arrows in the photo at left point to tree wounds created by dogwood borer activity. Piles of reddish-brown frass have pushed out of active borer sites while old borer wounds seem to ooze tree sap (dark black staining on bark).
   Dogwood borers seem to more of a problem in young, non-bearing orchards. Problems with this insect seem to disappear when trees begin nut production and a regular insecticide program is adopted to control nut feeding pests. Insecticides aimed at pecan nut casebearer and pecan weevil will serve to control both dogwood borer adults and emerging larvae.
   Because I found extensive dogwood borer damage all across my young orchard, I will be applying a trunk spray of chlorpyrifos (Lorsban) to knock back the existing borer population. However, if I had been paying closer attention and recognized the borer threat earlier, an early May trunk spray would have been most effective.

Monday, July 21, 2014

Mid-summer maintenance of a top-worked tree

     I've had some outstanding growth on my new grafts this summer and it was time for a little mid-summer tree maintenance. In the photo at right, you can see that the scion has outgrown the bamboo bird-perch that I attached during the grafting process. From this distance, it looks like the new graft is developing into a strong central-leader tree but a closer look reveals the need for some additional summer pruning.
    Even though I trimmed off all the stump sprouts back in June, new sprouts have appeared (photo at left). It is amazing to see green shoots literally pop out of the side of the trunk in such a short time. But like I did back in June, I cut off all new trunk sprouts using my pruning shears.
    Next I inspected the top of the scion.Wow, look at all those stalked buds growing at each leaf axil. If I allow shoots to develop from all these stalked buds, I'll end up with a bushy topped tree and no central leader. It a good thing I brought along a step ladder because I needed it to reach the top of the tree and carefully prune out all these unwanted shoots.
    With all my summer pruning efforts focused on pushing the tree to develop a dominate central leader, I knew it was time to replace the bamboo bird-perch with a more substantial tree-training stake (photo at left). I made my stakes by ripping a 10-foot-long 2 x 4 into 4 stakes measuring 3/4 inch by 1.5 inch (remember a 2 x 4 has the actual dimensions of 1.5 X 3.5 inches).  I attached the stake to the tree using electrical tape (duct tape would also work). I then tied the scion to the stake using 8 mil thick green plastic tape (1 inch wide).
    Judging from the rate of growth I'm seeing so far, this graft union should be completely grown over by the end of next summer (2015). The stake I attached this summer should serve to protect the scion from wind breakage until that time.
   While removing the bamboo bird-perch, I also removed the plastic bag and foil covering the graft union (photo at right). In the past, I've had problems with insects  tunneling in the wood under the wraps and slowing the healing process.
    When I removed the wraps, the bark was almost dripping with moisture. All that moisture can accelerate wood decay at the stock's cut surface so I decided to let the graft union dry out. However, the sudden exposure of the graft union to full sun can cause a sunburn that damages the tree's cambium.  To protect the graft union, I'll use white latex house paint as a sun block.
    I allowed the graft union to dry off while I attached the new tree stake and pruned the central leader (described above). Next, I grabbed a paint brush and painted the graft union (photo at left). Don't be afraid to slap it on thick. Remember the paint's role is to block out the sun and reflect the heat.

Use water-based latex paint only!!  I use exterior flat white.

     When I paint a graft union, I make sure to cover the entire area the was once covered by foil and plastic. This includes the top the stock and the lower portion of the scion (photo at right). The white paint also serves as a visual reminder of which trees have been grafted and the location of the graft union.

   If you would like to go back in time to see how I've top-worked and trained this tree, check out these posts;

1. Changing pecan cultivars by top-working

2. Forcing a bark graft

Monday, July 14, 2014

Identifying nut drop caused by hickory shuckworm

   Most growers recognize the hickory shuckworm as a late season pest that tunnels inside pecan shucks late in the growing season. However, an earlier generation flies in early July and lays eggs on young nuts. In the photo above, the red arrows point to oviposition scars created by female shuckworm moths to deposit eggs in the shuck.
    Once she lays eggs inside the shuck, she scrapes some scales off her abdomen and places them over the hole in an effort to disguise the eggs from predators and parasites. The white halos around each scar are the scales left behind by the female moth.
    At this time of year, it takes about three days after a nut is punctured for that nut to fall from the tree. Fortunately, the generation of hickory shuckworm that causes this kind of nut drop is usually quite small and does not cause enough damage to warrant insecticide treatments.

Friday, July 11, 2014

Planthoppers on pecan

    While trimming my grafts,  I came across a patch of white cottony material on the stem of one of my young trees (photo at right). After looking more closely, I could see a small colony of nymphs hiding within the patch of white fluff. I also spotted a stream of small ants tending the white nymphs.
   The nymphs in the photo are the immature form of the citrus flatid planthopper (Metcalfa pruinosa). Adult planthoppers are small, gray, wedge-shaped insects that spring off the stems of trees when disturbed (photo below). Nymphs are wingless and remain clustered in a group until they reach maturity. Both nymphs and adults are sap feeders, piercing the bark of young trees to feed.
   The ants in the photo are tending the planthopper nymphs. They collect the sugar-rich honeydew secreted by the planthoppers while protecting the nymphs from predators and parasites.
   Planthopper feeding does not pose a serious threat to young pecan trees. Although a large white patch on the stem of a young tree may look bad, an insecticide treatment is not necessary. 

Adult citrus flatid planthopper feeding on young pecan tree

Wednesday, July 9, 2014

Nut expansion begins for early ripening pecan cultivars

    Earlier this week I collected some nut samples from 3 pecan cultivars. The first tree I visited was a Henning, one of the earliest ripening pecan cultivars we have in our collection. I then cut nut clusters from a mid-season ripening Kanza tree and a late-ripening Maramec tree. At this point in the growing season, you can see that Hennnig nuts have already started to plump-up and have entered the phase of rapid fruit expansion (photo above). Kanza and Maramec still looked to still be in the post-fertilization phase; just waiting around to start fruit expansion.

Cross sections of a Henning, Kanza, and Maramec nuts (left to right)
    Cutting into the nuts confirmed my suspicions about the stage of nut development for each of these cultivars (photo at left). The cotyledon of the Henning nut has expanded into a large heart shape; the first indicator that the nut has started into rapid fruit expansion. In contrast, the Kanza and Maramec nuts had small oval-shaped cotyledons. Rapid fruit growth for these  two later-ripening cultivars has not yet begun. 

Tuesday, July 8, 2014

Fall webworm colonies becoming obvious

    Driving along the highway, I've started to notice numerous colonies of the Fall Webworm. Webworms create a white web around their colony of 30 to 100 caterpillars (photo at right). The web serves as protection against both predators and parasites. Each evening the caterpillars work to extend the web further out into the canopy to capture fresh green leaves to feed on. The webs we are seeing now represent the first summer generation of the fall webworm. A second generation will appear in late August to early September.

   If you look closely inside the web, you will see an army of yellow to rust-orange caterpillars feeding of pecan leaves (photo at left). At maturity these caterpillars will grow to 1.5 inches long and be covered with long white hairs. Eventually, larvae leave their protective web and drop to the ground. The caterpillars will then crawl into ground-cover litter and pupate. A white moth will emerge from the pupal case and fly up into the trees to initiate a second summer generation.
   Many folks believe that they need to penetrate the web with an insecticidal spray to control this pest. Since the caterpillars are continuously expanding their web in a quest for more green leaves, applying an insecticide on the foliage surrounding the web will effectively control this pest.
    In commercial pecan groves, there should be more than 5 colonies per acre to justify an orchard wide insecticide treatment. This spring, I have seen very few webworm colonies in pecan groves that were sprayed for pecan nut casebearer. It seems that the residual action of the earlier applied insecticide treatment has kept early-hatch webworms in check.

Friday, July 4, 2014

hoo... hoo..... is sitting on my bird perch

     Every year when I give grafting schools, I stress the need to attach a "bird perch" on the tree to protect the scion from birds landing-on and breaking-over the newly attached graft. Common song birds that like to perch on new grafts include; red-winged black birds, meadowlarks, and sparrows, bluebirds and starlings.  I never expected that an owl would perch on one of my trees.
    About a month ago, my neighbor stopped to tell me he had seen an owl perched on the bamboo stake I had attached to a tree I had top-worked. He was amazed that my bird perch was strong enough to hold such a large bird.  I knew a pair of Barred owls were nesting on my farm because I had recognized their distinctive call (sounds like--"Who cooks for you, who cooks for you all") earlier this spring. Even though I heard them calling, I never got a good look at them until this week.
    The other evening, I was finally able to photograph one of our resident Barred Owls. The owl was perched on a steel fence post that holds one of my tree cages in place around a seedling pecan tree (photo above). From the owl's perspective, this was the perfect spot to hunt for mice and voles that live in the turf between my young trees. Barred owls can grow to 25 inches tall with a wing span of 3.5 feet. Barred owls will also dine on squirrels, so I hope this pair of owls stays around for many years to come.

Thursday, July 3, 2014

How pecan branches can tell a story

   I was in the orchard looking at our nut crop when I spotted a group of limbs with a story to tell (photo above).  To the causal observer, this photo may look like a simple collection of leaves, twigs and two nut clusters but let me point out several things and the entire recent history of this pecan tree comes to light.

   I'll start with last year's nut crop. The red arrow points to a dark-grey and dried up twig (photo above). This was the pedicel that held last year's nut crop. You can even see the attachment scars where the nuts were held. In time, this old pedicel will form an abscission layer at the point it connects to the main stem and will fall from the tree. However, simply finding this old pedicel tells me that this tree bore nuts in 2013.

     Once a twig produces a cluster of nuts at the terminal, vegetative growth usually stops for the year. However, weather conditions in 2013 helped to promote a second flush of vegetative growth. If you remember back to last summer, we experienced a dry early summer followed by a wet period beginning in late July. The sudden resupply of soil water encouraged two buds right below the nut cluster to break and grow. In the photo above, yellow arrows point to these second-flush shoots.

   In early April of this year, the second-flush shoots began spring bud-break just like all other one-year-old shoots on the tree. However, on April 15, cold weather froze emerging buds killing all exposed green tissues. In the photo above, the orange arrows point to frozen buds still clinging to the tree. Fortunately, pecan trees are not so easily defeated by a little cold weather. Buds lower on the second-flush shoot were fully dormant at the time of the freeze. These buds survived the cold and grew into this year's new shoots.

   In the photo above, the red arrows point to the shoots that developed after the spring freeze. Since these shoots emerged from primary buds they produced pistillate flowers and have since set nuts (in red circles).      
    In the end, a simple, close inspection of twig growth tells the recent life story of this tree. Weather conditions caused a secondary vegetative flush in 2013 but froze emerging buds in 2014. However, in spite of the weather, this pecan tree produced nuts in 2013 and 2014.