The end of the rainbow

 

  You may have heard the tale of a pot of gold at the end of a rainbow. But last night, I saw a rainbow that ended in my pecan grove which is a sure sign that I'll be harvesting a pot of golden pecan kernels in the Fall.

End-of-summer graft check-up

    Its Labor Day weekend and it time for an end-of-summer graft check-up. I've had some great growth on my bark grafts with many scions growing over 5 feet this summer (photo at right). This tree appears to have more leaves at the top of the tree than in the middle and lower portions of the scion. What you are seeing is the result of a normal slow-down of shoot growth that happens towards the later part of the summer. As shoot growth slows, the distance between buds decreases. Likewise, the distance between leaves along the stem becomes shorter as growth slows. More leaves in a shorter stem span gives this tree its top-heavy appearance.

    All summer long I've been removing stalked buds from this tree so I wanted to make sure new stalked buds hadn't formed since I checked the tree back in late July. I looked at the top of the tree (photo at left) and discovered only sessile buds and a well formed terminal bud. This is good news. This tree has stopped growing and can now start hardening-off in preparation for winter's cold.

    Not all my trees have stopped growth for the year. The graft pictured at right was still creating new leaves and had formed stalked buds near the top of the tree. My first step was to prune all the stalked buds just like I had been doing all summer. But at this time of year, I made one more cut. I pruned out the tip of the central leader to encourage the tree to start shutting down. A scion that grows vigorously, well into the Fall, is at greater risk for mid-winter cold injury.

    I also checked on the condition of each tree's graft union (photo at left).  It appears like the tree is healing over nicely. The scion has covered over nearly three quarters of the stock's cut surface. The white paint I applied in early August served to prevent sun-scald to the union and inhibit insects from feed on callus tissue. However, the best thing about the white paint is that now I can look across the field and easily spot which trees I've grafted.

Minimal scab in 2014

Scab lesions on Dooley pecans

    Up until late August, the 2014 growing season in SE Kansas can best be described as having below average rainfall. Back in June, we were receiving regular rain showers prompting us to apply a fungicide along with our pecan nut casebearer spray. Once July hit, we started missing significant rain showers and our grove started to dry out. With this year's dry mid-summer, pecan scab never became a serious threat to our pecan crop.
   This morning I visited trees of two cultivars that are normally very susceptible to pecan scab; Dooley and Peruque. I was interested to see how these two cultivars have faired with the minimal scab spray program they received this year.

Scab lesions on Peruque pecans

    Scab lesions can be seen on the shucks of both cultivars. However, in both cases, the scab lesions were small and largely superficial. Just last year, we didn't even harvest our Dooley crop because scab had destroyed every single nut. In 2013, Peruque wasn't much better as we were forced to discard numerous scab infected stick-tights off the cleaning table. What a difference a year makes!
   
  

Kernel fill progressing with the return of summer heat

    This week's high temperatures, especially night-time temperatures that didn't drop below 75 degrees F, have helped pecan nut development advance. This morning I collected nuts from 5 pecan cultivars to check on stage of nut development (photo at right). Of the cultivars I harvested, only Giles nuts are still expanding in size. Colby, Goosepond, Peruque. and Kanza have all completed nut expansion and are now filling kernel.

    By cutting each nut in half I could see how these 5 cultivars were progressing in terms of kernel fill (photo at left).  It looks like Goosepond has almost completed kernel filling while Peruque has only a slight crease down the middle of each kernel half to fill. In comparing Goosepond and Peruque, look carefully at the inner shell partition that separates the two halves of these pecans. Notice how the inner partition in the Goosepond nut is thinner and has turned dark brown in color as compared to the thicker, light-tan partition in the Peruque nut. A change in color of the middle septum, from light to dark, is an indication that nut kernel expansion has fully compressed the inner packing material inside the shell.  
     The Colby nut has developed some solid kernel but you can still see the translucent 'jelly' layer that indicates rapid deposition of new kernel material. The slight thickening of the seed coat  (a thin jelly layer) reveals that Kanza has only just begun kernel deposition. The kernel of the Giles nut is still expanding and the nut has not yet reach full water stage.
     This year, kernel development seems to be behind schedule. Although we have suffered through some stifling heat this past week, the summer of 2014 has been cooler than normal and those cool temperature have retarded nut development. Lets hope we catch up before frost hits this Fall.   

Pecan leaves covered in honeydew

Honeydew on pecan leaflet

   Have you noticed a shiny and sticky substance covering your pecan leaves this summer (photo at right). That  substance is called honeydew and it is excreted by black-margined pecan aphids feeding on the leaves. 



   Turn a honeydew-coated leaf over and you will find several aphids lined up along the major leaf veins (photo below). Immature aphids are yellow and wingless. Adult aphids also yellow but have clear wings with a streak of black along the outside edge.

Black-margined aphids feeding on pecan

Harmonia lady beetle

Lacewing egg attached by a silken thread

Spider hiding in webbed nest between nuts

   Fortunately we have several beneficial insects in the pecan grove that feed on aphids helping to control this sap feeding insect. Among the most active aphid predators are the lady beetles and the lacewings. Pecan canopies are also populated by a large number of spiders that will feed on aphids.     
   In most cases, we do not try to control black-margined aphids with insecticides. Over-use of insecticides usually leads to the elimination of beneficial insects, creating a huge rebound explosion in aphid populations.   

Spring frost impacts Pawnee nut development

     Back on April 15, we had a freeze that killed emerging pecan buds on the lower portions of tree canopies. As the spring flowering season arrived, I noticed that primary buds at the base of frost damaged shoots emerged to produce pistillate flower clusters. Today, I used our hydraulic lift to check nut development of Pawnee trees that had suffered cold injury on the lower portions of their canopies.

   Overall our Pawnee trees look to be bearing a light to medium crop (following last year's big crop). In the photo at right, you can see that the shoot cut from the upper portion of the canopy (above the frost line) broke bud from the terminal of last year's wood and produced three new shoots each bearing a cluster of nuts. On the shoot cut from the lower portion of the canopy, you can see a frost damaged terminal (in red oval) and two nut bearing shoots that emerged from the lower portion of that frost damaged shoot.
   

    In collecting nut samples from the upper and lower portions of Pawnee trees, it looks like last Spring's frost impacted nut size (photo at left). However, what you are actually seeing is a difference in nut development stage created by differences in time of bud break. The shoots above the frost line started to grow and develop sometime during the first week of April. Below the frost line, initial bud break was frozen and basal buds didn't begin to emerge until late April.

    When I cut open nuts from upper and lower portions of the canopy, I found that the delay in time of bud break for shoots in the lower canopy is now displayed as a delay in nut development. In the photo at right, the nut collected from the upper portion has  expanded to roughly 3/4 water stage while the nut from lower in the canopy is at 1/2 water.
    Come this fall, I wonder if I will time of shuck split will differ with tree height. I bet it will.

Spraying for stinkbugs and shuckworm

   After fighting through some mechanical problems with our tractor and sprayer, we finally sprayed the pecan grove to control stinkbugs and shuckworm today (photo at right). We had planned to spray earlier in the week in response to the nut drop we have been seeing but we ended up having to wait for parts to arrive.
    We applied Warrior II at the rate of 2.56 oz/ac. But, "How much do I put in the tank?" you might ask. Many growers are frustrated by fact that suggested rates on pesticide labels are given as amount of product to apply per acre rather than amount to mix in 100 gallons of water. Pesticide manufacturers are not trying to make your job more difficult, they are only following EPA mandates.
   The proper way to determine how much pesticide to put in the tank is to determine how much water is needed to spray an acre of pecan trees. However, we have found that the amount of water needed varies with both time of year and tree size. We use less water per acre during springtime casebearer sprays and more water per acre during late-summer weevil sprays. There are just more leaves to cover late in the season than earlier in the year. In addition, large native trees take far more water per acre to cover than a young orchard of grafted trees.
    With experience, I have learned to assume we apply 100 gallons of water per acre in calculating how much pesticide to add to our 500 gallon tank. I then use the maximum recommended rate as listed on the pesticide label. In spraying the grove, I never rush the process. I drive slow enough to make sure to get complete coverage of the canopy. The leaves need to be covered, not dripping wet.    

Webworm moths laying eggs

   Today, I found the first indication that the second generation of fall webworm is on its way. On the underside of a pecan leaflet, a female webworm moth was busy laying a large cluster of eggs (photo at right). As you can see, the adult moth is white and about 3/4 inch long. The female moth in the photo has almost completed laying a dime-sized egg mass (partially hidden under her wings). As she lays her eggs, she covers the eggs with scales scraped from her abdomen. This gives the egg mass a fuzzy white appearance.
    The eggs will start to hatch in about 7 days. The hatched larvae will immediately start feeding on pecan leaves and spinning their protective webbing. Based on the size of the first summer generation, we will start to notice a large number of new webworm colonies by the end of August.

Early August nut drop

    Over the past week, I've noticed  quite a few green pecans have dropped to the ground (photo at right). Since all our pecans are still in the kernel expansion phase of nut development (i.e. the water stage), any insect that punctures the nut will cause nut drop. At this time of year we have three insects currently feeding on nuts; hickory shuckworm, pecan weevil and stinkbugs. I picked up a handful of dropped pecans and used my knife to determine why the nuts were aborted.

    In our orchard, the vast majority of nuts dropping from trees were damaged by stinkbug feeding. I also found evidence of hickory shuckworm activity. Nuts damaged by stinkbug were still filled with embryonic fluid (water) but the inside of the seed coat had turn dark brown to black in color (nut on right in photo above). In contrast, hickory shuckworm infested nuts were dry inside and I could see signs of larval tunneling. In the photo above, the red arrow points to a tunnel created by the shuckworm. I did not find any weevil punctured pecans in our orchard.
   We will be spraying the orchard this week to combat shuckworm and stink bug. We'll use Warrior II insecticide at the rate of 2.56 oz/acre.

Rain, weevils, and nut development

   It rained a little over one inch on Thursday and that's usually enough moisture to loosen up the soil and allow pecan weevils to start emerging. But female weevils can't lay eggs inside a pecan until all the embryonic fluid inside the expanding nut is replaced by kernel tissue (i.e. water stage changes to dough stage).

   Over the past several weeks, I have been cutting open nuts of several pecan cultivars to determine stage of kernel development. However,  I thought it would be a good idea to check on the status of our native crop. So I climbed up into our hydraulic lift and grabbed nut samples from 9 native trees (photo above).
   The first thing you should notice is that native pecans are generally smaller than the improved cultivars I photographed earlier this week. The second thing to notice is the wide variation we find among natives in size and shape. After cutting into each of these nuts I found that many of these nuts are still expanding.

    The photo at left shows the cross-section of each native nut. By cutting into each nut I found that kernel development ranged from 1/4 kernel expansion (nut B) to the very first stage of kernel deposition (nut H). None of these nuts would be suitable for pecan weevil egg laying.
    The early pecan weevils that will emerge this weekend will migrate to nut clusters seeking a mate and feeding on developing pecans. Nuts in the water stage and punctured by weevil feeding will stop expanding and drop from the tree.
    If your grove has a history of heavy pecan weevil damage you might consider applying an insecticide to reduce the weevil population as early as next week. At the Pecan Experiment Field, we will be applying an insecticide starting on Monday that will be aimed primarily at stinkbug control but should also control early emerging weevils.

Early ripening cultivars enter water stage

Goosepond 4 August 2014

    Cutting nuts open and checking on nut development during this first week in August gives me a pretty good idea when a cultivar will ripen in the fall. Today, I decided to look at several cultivars including cultivars new to our trials as well as some old standbys.  I took a photo of each cultivar that included a whole nut and nut cut in cross section that reveals the current stage of nut development. The photos were all taken using the same scale so you can judge differences in nut size between photos.

Lucas 4 August 2014

   Lucas and Goosepond were the most advanced in term of kernel development. These two cultivars are currently in the water stage pointing to a late September nut ripening date.

Mullahy 4 August 2014

     Mullahy had pushed kernel expansion to about three quarters of the way to the base of the shell. I expect Mullahy to ripen shortly after Goosepond and Lucas but still before the first of October.
    Next I found several cultivars at the one-half kernel expansion stage. These included Hark, Kanza, Major and Posey. These four cultivar should ripen during the first 10 days of October.

Hark 4 August 2014

    I was especially interested in seeing how Hark was developing compared to some of our better known cultivars. The original Hark tree is a seedling tree planted in Alexis, IL (a small town outside of Galesburg). However, the seed was originally collected from an orchard of grafted trees near Moberly, MO. The scaly bark of Hark is similar to  the bark of a Major tree which made me think that Hark may have had Major as one of its parents. Now that I have cut open a Hark and compared it to Major and Kanza (another Major progeny) my suspicions about Hark's ancestry has strengthened. However, simply sharing a similar stage of nut development doesn't prove Hark is related to Major. Posey was at a similar nut development stage and but has no genetic link to Major or Kanza.
    I think the most important thing I learned today about Hark is that, just because the original tree originated at the far northern limits of pecan culture, it doesn't mean that this cultivar will mature nuts super early.
   And finally, just to give you an idea of how far ahead our northern cultivars are as compared to a more southern cultivar, I cut open a Stuart pecan. By early August,  Stuart has just barely entered the nut expansion phase. Stuart won't ripen until early November and we might get a killing freeze before it splits shuck. 
 
   

Kanza 4 August 2014

Major 4 August 2014

Posey 4 August 2014

  
  

Stuart 4 August 2014