Tuesday, August 26, 2014

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!

Friday, August 22, 2014

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.   

Tuesday, August 19, 2014

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.   

Friday, August 15, 2014

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.