Monday, August 31, 2015

Late season aphids

   The leaves of our pecan trees are starting to take on a sticky and shiny appearance (photo at right). That's because foliage is now covered with honeydew, the by-product of aphids feeding on the underside of the pecan leaves. This year, honeydew coverage of the leaves has been minimized by an unusually large amount of summer rainfall washing the leaves clean. Despite the rain, aphids are still at work, creating even more honeydew.
    I've seem some development of black sooty mold on the leaves (photo at left). This black fungus grows on honeydew and does injure the leaves directly. Indirectly, sooty mold harms the foliage by blocking sunlight and reducing photosynthesis.

   Turn over a leaflet and you'll see the insects that are creating all that honeydew. During the peak of an aphid outbreak, you will find all life stages of the black-margined aphid feeding on pecan tree sap. In the photo above, a winged adult can be seen feeding on the leaflet's main mid-rib. Note the black markings along the outer edges of the insect's otherwise clear wings. Its obvious how this insect received the common name--black-margined aphid.
    Also in the photo you can see various sizes of wingless aphids nymphs. If the nymphs can avoid being eaten by lady beetle or lacewing larvae, they will all grow into winged adults. As a nymph grows in size it must shed its old, smaller exoskeleton before growing into a new larger exoskeleton. Cast-off exoskeletons appear in the photo as white to grey bits of fluff.
   Aphid populations can grow rapidly but eventually crash as pecan leaves become less suitable for aphid feeding. Spraying pecan trees for aphid control seems only to create insecticide resistant strains of the aphid. In our orchard, we have chosen to let the aphids run their course and not spray to control the population.      

Tuesday, August 25, 2015

That tree is not a Giles!

   Years ago, we started a scionwood orchard to produce high quality scions for growers to graft onto their seedling pecan trees.  When we established this orchard, we took great care to graft with scions from known trees that were true to cultivar.  But several years ago, I noticed that one of the trees marked "Giles" (tree 17 in row 6) in the scionwood block ripened well ahead of all the adjacent Giles trees. Even though the nuts are roughly the same size and shape, I noted that nuts collected from the tree we are now calling, SWB617, has a different shuck appearance. Giles nuts have prominent wings along shuck sutures. SWB617 does not. (photo above).

     I cut open a Giles and a SWB617 nut yesterday to check on nut development (photo at left). Wow, what a difference. Giles was still in the water stage and SWB617 had packed the inside of its shell with kernel.
    The question is--where did this early ripening tree come from? I looked at the trunk of the tree and it certainly looks like it was grafted near ground level just like all the rest of the Giles trees in the same row. But how could one piece of unknown scionwood get mixed up into a whole bag of Giles wood? Not only that, SWB617 doesn't look like any cultivar we have on the farm. I'm now convinced that the original Giles graft died and the seedling root grew up to take its place. That would make SWB617 an open-pollinated Giles seedling (we used Giles seedlings to start the planting).
   Last year, SWB617 produced a nut that averaged 5.79g and had 56.61% kernel. For comparison, Giles averaged 6.36g and produced 52.66% kernel. SWB617 matured during the last week of September in 2014 and showed little or no scab infection. In 2015, SWB617 has some scab but not as bad the scab found on adjacent Giles trees. In contrast, SWB617 had more powdery mildew on nuts than found on Giles nuts.  Because this tree ripens early, it will definitely be worth watching. I've even grafted a few more trees of this seedling to see how it acts as a grafted tree.
   So in the future, when I mention a tree called SWB617 you will know a little of its background and why I labeled it based on the location of the tree at the research station--Scion Wood Block row 6 tree 17.

Monday, August 24, 2015

Spraying for pecan weevil

   In our little corner on SE Kansas, we've had over 6 inches of rain in a 5 day period. While the rain is welcomed at this time of year to help fill pecan kernel, wet soil conditions have lead slow steady emergence of pecan weevils. So today,  with sunshine, calm winds, and cool temperatures, we applied a second dose of insecticide to keep weevils in check (photo at right).  This time we applied Sevin insecticide making sure our air-blast sprayer covered the entire tree canopy.

Friday, August 21, 2015

Pecan kernels fill during August

    Yesterday, I collected nut samples from nine different pecan cultivars to check the progress of kernel filling. I was somewhat surprised to find so many cultivars still in the water stage this late into August. Lets take a look at what I found.
    Cultivars with early ripening dates have started packing the inside of their shells with nut kernel (photo at right). Warren 346, one of our earliest ripening cultivars, has developed enough solid kernel to put pressure on the inner wall partition, compressing those tissues and causing a distinctive color change (from tan to reddish brown). Peruque and Colby have laid down a thick layer of solid kernel but both cultivars are less than half way towards full kernel development.
   This next set of three cultivars (photo at left) illustrates how the kernel filling process begins. The Mandan nut is in the full water stage. Liquid endosperm is held inside a thin membrane that will eventually form the outer skin on the nut kernel. If you look closely at the kernels of the USDA 75-8-5 and Major nuts, you will see a layer of translucent tissue forming inside the kernel's skin. This is the very beginning of  the kernel filling process. As more kernel material is deposited the translucent layer will begin to turn white in color. In the photo of the  Colby nut (above), you can see a layer of white kernel tissue next to the seed coat. Inside the white layer is a layer translucent kernel. Just by careful observation, we can see exactly now pecans fill their kernel--from the outside inwards.
   This last set of cultivars (photo at right) illustrates just how much packing material is present inside the shell before a kernel reaches its full size. All of the white tissue outside the seed coat but inside the shell will be compressed by the developing kernel. When the kernel attains full water stage the developing kernel compresses the packing material enough to cause a color change from white to rusty brown. The zones of greatest compaction are found along the inner wall partition and dorsal groves (see Kanza photo at right).
    As more and more solid kernel is deposited, the packing material is compressed tightly against the inside the shell until it becomes hard, brown and brittle. When nuts are cracked after harvest, the brown dust created by the shelling process is all that remains of the nut's packing material.

Sunday, August 16, 2015

Emerging fall webworms killed by insecticide aimed at pecan weevil

    During the first week of August we sprayed our pecan grove with an insecticide to control emerging pecan weevils and stinkbugs. A few days later, I reported seeing many fall webworm egg masses on the underside of pecan leaves. Actually, I found these eggs masses while spraying some young trees to control weevil. Three days after making an application of Warrior insecticide, fall webworm larvae started to emerge from their eggs. Once they emerged they contacted the pesticide and started dying. In the photo above, all the dark colored larvae have been dead for quite some time. The yellow larvae are still alive but are so sick they can't make it off the egg mass to start feeding on green leaf tissue. These larvae will die shortly.
     As it turn out, my efforts to control weevil and stinkbugs have also controlled fall webworm.

Wednesday, August 12, 2015

Nut thinning Lakota pecan with a trunk shaker

  When we first released the Lakota pecan cultivar, I warned growers that, when this tree matures (20+ years old), it tends to over-produce. Over-production reduces nut quality at harvest and limits return bloom the following year. To combat over-production, we used our trunk shaker to remove a portion of our Lakota crop by lightly shaking the tree during the water stage of nut development (photo at right).
   Before shaking, I checked the stage of kernel development of our Lakota trees by slicing open several nuts. Today, Lakota was not at full water stage by close enough for tree shaking purposes (photo at left).  As we moved through the orchard, we discovered that some Lakota trees were far more over-loaded than other trees. By watching each tree during the shaking process, I can remove more nuts on the trees that are severely over-loaded and fewer nuts on trees with a lesser crop load.
    When thinning a pecan crop with a tree shaker, it is important not to judge the amount of thinning needed by looking at the number of nuts shaken to the ground (photo at right). If seeing a bunch of green nuts on the ground makes you nervous, I would strongly advise not grafting Lakota in your pecan grove. Lakota may not need nut thinning every year but you will need to thin nuts off of this cultivar during years of heavy nut set.

   To judge how much thinning is enough, it is best to look up at the canopy to see how many nuts are left in the tree after shaking. It is hard to capture crop load with a camera but the photos above show the exact same area of tree canopy before and after tree shaking. We aim at shaking the tree long enough to reduce the Lakota crop down to about 60% fruiting shoots. When nut thinning, we have found it best to have the shaker operator directed by a canopy spotter trained to judge the crop load left in the tree.

Tuesday, August 11, 2015

Second summer generation Fall webworm egg masses spotted

    I was mowing around my pecan trees when I spotted several dime-sized egg masses deposited on the undersize of pecan leaves (photo at right). The eggs are very light green in color but are largely covered by a layer of white fluff. This is the start of a new Fall webworm colony. Female webworm moths lay their eggs in a cluster on the underside of a leaf then cover that egg mass with scales rubbed off of the moth's abdomen. The female moths cover their egg masses in this way to hide the eggs from egg parasites.

   Driving down the highway, I noticed that the 2015 spring brood of fall webworm on roadside trees was fairly large. And judging from the number of egg masses I've already seen, the fall brood will be even bigger. I even found two egg masses on a single pecan leaflet (photo at left).
   With recent rains, pecan weevils have started to emerge and we have already sprayed the pecan grove to control weevils and stinkbugs. It looks like our pesticide application will also help keep webworms in check. Additional weevil sprays later this month should control any additional webworm colonies that arise from egg masses deposited later in August.

Monday, August 10, 2015

Mid-summer pecan cultivar evaluation

    Last week, I pulled nut samples from 14 pecan cultivars to get a quick assessment of performance for the first half of 2015. I was most interested in disease susceptibility but also I wanted to check on nut development during the first week of August. My observations are listed next to the photo of each cultivar and a cross section view of a nut (so you can see kernel development). The cultivars are presented in alphabetical order.
Faith (6 Aug. 2015)
  1. Light level of scab following 2 fungicide applications in June.
  2. Medium to heavy crop load
  3. Nut development at 1/2 water stage

Gardner (6 Aug. 2015)

  1. Light scab follow 2 fungicide applications in June.
  2. Nut development at 3/4 water stage.
  3. Moderate crop load

Giles (6 Aug. 2105)
  1. Light scab following 2 scab sprays in June.
    Medium to full crop load.
    Nut development at 1/4 water stage.

Hark (6 Aug. 2015)

  1. No scab, received a single fungicide application with casebearer spray.
  2. Light crop on young tree.
  3. Kernel at 3/4 water stage.


Kanza (6 Aug. 2105)
  1. No scab, clean shucks. Received a fungicide with casebearer spray in early June.
    Medium to heavy crop load.
    Kernel  development at 3/4 water stage. 


Mandan (6 Aug. 2015)
  1. Scab and powdery mildew on shucks following 2 fungicide applications in June.
  2. Moderate crop load.
  3. Kernel between 1/2 and 3/4 water stage.
  4. Shell more narrow at the base.

Mullahy (6 Aug. 2015)

  1. Serious scab with a single scab spray with casebearer spray in early June.
  2. Light crop on young tree.
  3. Kernel at full water stage. 

Norton (6 Aug. 2015)
  1. Clean shucks with 2 fungicide applications in June
  2. Moderate crop.
  3. Kernel at full water stage.
  4. Heavy shell and similar nut shape makes Norton the scab-free version of Colby. 

Osage (6 Aug. 2015)
  1. No scab but susceptible to powdery mildew
  2. Moderate crop load
  3. Kernels at full water stage

Peruque (6 Aug. 2015)
  1. Severe scab after a single scab spray in early June.
  2. Scab has reduced nut size.
  3. Kernel at 3/4 water stage.
  4. Moderate crop load.

Surecrop (6 Aug. 2015)
  1. No disease following 2 fungicide applications in June.
  2. Very light crop load.
  3. Kernel at 1/2 water stage. 

USDA 64-11-17 (6 Aug. 2015)
USDA 64-11-17
  1. Moderate scab following 2 scab sprays in June.
  2. Heavy crop load.
  3. Kernel  approaching 3/4 water stage.
  4. Nut tapered at the base. 


USDA 75-8-5 (6 Aug. 2015)
USDA 75-8-5
  1. No scab visible after  2 fungicide applications in June.
  2. Heavy crop on young tree (crop load enough to reduce kernel quality).
  3. Kernel at 3/4 water stage.

Warren 346 (6 Aug. 2015)
  1. No scab but powdery mildew on shucks
  2. Very light crop
  3. Kernels at full water

Thursday, August 6, 2015

Spraying for stinkbugs and early pecan weevil

    As I mentioned in yesterday's post, we've been seeing quite a few nuts drop from stinkbug feeding. On top of that, the 2 inches of rain we received yesterday should bring out the first flush of pecan weevils. So this morning we decided to take advantage of a cooler day with light winds to spray our pecan grove (photo above). This is only the second time we've sprayed our native trees in 2015 so we included both an insecticide and a fungicide. We used Warrior II for stinkbugs and weevil and Headline for scab.

Wednesday, August 5, 2015

Mid-summer nut drop

    A quick walk out into the pecan orchard at this time of year and you might spot several green nuts on the ground (photo at right). A quick look at the fallen nuts and you will probably find some scab lesions or large patches of discolored shuck tissue. However, the primary reason these nuts have dropped during the first week of August is stinkbug feeding. It is often difficult to identify stinkbug damage by inspecting the exterior of the shuck. If you look carefully, you might find stinkbug feeding scars on the outside of the nuts but, with numerous scab lesions also present, these small feeding scars might be hard to see.
    The easiest way to confirm stinkbug feeding is to cut open dropped nuts and inspect the developing kernel. If the interior of the nut including the developing kernel is dark brown you can be assured that stinkbugs have attacked the nut.
   This morning we received nearly 2 inches of rain which should stimulate the emergence of pecan weevil. These weevils will also start feeding on nuts causing a nut drop similar to the drop caused by stinkbugs. You can distinguish weevil feeding from stinkbug feeding by the size of the hole drilled through the shuck. Weevils make a much larger hole in the shuck and often leave a pattern of foot marks around the feeding site. Weevils will continue to feed on nuts until kernels reach the dough stage.
   Once this rain system passes all the way through our area, we plan to spray our pecans to control the stink bug population and kill off early emerging pecan weevils.