Friday, September 8, 2017

Pecan trees dripping sap?

    A lot of pecan growers have noticed that the leaves of their trees look like they are constantly wet (photo at right). Touch the leaf and you'll find the leaf is covered in sticky tree sap. Park a car under a pecan tree and the windshield will soon be dotted with sap falling from the tree. Pecan tree sap is not actually dripping from leaves but, what you see is the exudate from pecan aphids.  

     An outbreak of black-margined pecan aphids feeding on the underside of pecan leaflets is common in late summer. As these insects feed on pecan sap, they suck more fluid out the leaf than they can digest. Excess sap is excreted by thousands aphids and ends up coating the leaves below.
    In the photo above you can see aphids feeding on the underside of a pecan leaflet. The aphids insert their mouthparts into a main leaf vein and suck sap from the tree. Adult aphids have wings while immature aphids are wingless.
    The application of insecticides to control pecan aphids have largely proven fruitless. Pecan aphids develop pesticide resistance very quickly and aphid populations rebound quickly after being sprayed. In our pecan orchard, we concentrate our insect control efforts on pecan weevil and stinkbugs. Pecan aphid populations will eventually crash on their own. A good, heavy rain-shower will clean the leaves from the sticky sap and often help reduce aphid numbers. 

Wednesday, August 30, 2017

Pecan cultivars: Checking on scab infections

    I  spent some time collecting nut samples from 24 different pecan cultivars to check on pecan scab infection levels. This season we applied 3 fungicide sprays to our pecan orchard. So when you look at the photos keep that in mind. Cultivars with zero scab lesions are either scab resistant or our scab control efforts were able to keep the disease in check. In many cases, the shucks of some pecan cultivar show signs of scab infection but the level of infection is not severe enough to impact nut size, kernel fill, or shuck opening. Peruque is an example of a cultivar that was not protected by our scab spray program and scab has engulfed the entire nut (photo above). Colby is scab susceptible but our scab control program limited the disease to a few small of scab lesions. Norton and Osage are scab resistant--the black spots on these shucks are the result of limb rub.

    Major is a scab resistant cultivar (photo above). Kanza, Lakota, and Hark all have Major as one of their parents and are also scab free. Even though these four cultivars are scab resistant that does not mean that they are immune to all pecan diseases. The fungicides we applied to our grove this year have kept the shucks of Major and her daughters from contracting pecan anthracnose.

     The photo above show four early-ripening northern pecan cultivars. Warren 346 and Lucas were completely clean showing zero scab lesions. In contrast, Mullahy and Goosepond had scab lesions despite our spray program.

    Oswego is a seedling of Greenriver and both cultivars are scab resistant (Photo above). Posey and Surecrop are only slightly susceptible to scab and it appears that our spray program has prevented all disease on the shucks.

    Giles is a cultivar selected from a native grove just 2 miles from our research station. Giles shows scab susceptibility despite our efforts to control the disease (photo above).  Jayhawk and SWB617 have Giles parentage but Jayhawk is scab resistant. The scab resistance of Jayhawk must come from its unknown parent.  Chetopa is another local cultivar, originating as a native tree at the Pecan Experiment Field. Chetopa is not scab resistant but three fungicide applications have kept this cultivar clean.

   The final photo of cultivars show that Mandan, Pawnee, and Faith are all susceptible to pecan scab. Mohawk was free of the disease.  
   With the exception of Peruque, we have been able to control scab on susceptible cultivars to a point where we will see no economic losses. This year we invested about $60 per acre in disease controlling fungicide sprays. Judging from the crop I see on the trees, we should average over 1200 lbs. of pecans per acre. That more that enough nuts to pay for our spray costs.

Monday, August 28, 2017

Pecan cultivars: Checking on kernel development

    I collected nuts from 24 pecan cultivars and cut open nuts to check on kernel development. The four cultivars shown above are some of our early ripening pecans. All four have developed kernel tissue but they still have a ways to go until the nut becomes fully packed with kernel. The Peruque nut was heavily infected by pecan scab which translated into a smaller nut and poor kernel filling.

     The four cultivars pictured above represent some of our earliest ripening cultivars. Warren 346 and Lucas look pretty well packed with kernel but judging from the width of the inner-wall partition these two cultivars are still developing more kernel. Mullahy and Goosepond are only slightly behind Warren 346 and Lucas in terms of kernel fill.

    The four cultivars in the photo above illustrates the wide differences I observed in kernel development during late August. Pawnee and Faith have laid down a thin layer of kernel with Pawnee being further advanced than Faith. The Mandan nut has a developed a thin layer of translucent kernel (under-developed cells) while Mohawk is still in the water stage.

    These next four cultivars are all in the early stages of kernel deposition (photo above). Posey and Surecrop are ahead of Greenriver and Oswego. It is interesting to note that both Posey and Surecrop have prominent wings on the sutures of the shuck. Surecrop originated as a seedling in Carlinville, IL. Could it be that Surecrop is a seedling of Posey. Large suture wings are fairly rare among pecan cultivars.

    Although SWB617 is a Giles seedling, this cultivar is far ahead of its parent in terms of kernel development (photo above). On the other hand, Jayhawk, another Giles seedling, lags behind its parent. Chetopa is in the earliest stages of kernel development.

    This last group of four cultivars include Major and three of her progeny; Kanza, Lakota, and Hark (photo above).  Kernel development of Major and Kanza is roughly the same, while Hark appears slightly advanced. Lakota was still in the water stage and showed no signs of kernel development at this point in the growing season.

Friday, August 25, 2017

Pecan kernels filling - pests on the prowl

    The other day I cut open pecans from a few cultivars of pecans and discovered just what I expected. My pecans had started the kernel filling process (photo above, right). At this point during the growing season, the seed inside the shell has formed a thin layer of kernel tissue just under the seed coat. The amount of kernel deposition by late August is both weather and cultivar dependent. Earlier ripening cultivars will fill their kernels sooner that later ripening cultivars.

     As soon as pecans start to fill their kernels, two important pecan pests attack: Pecan weevils and squirrels. Since we've experience above normal rainfall for the month of August pecan weevils have been emerging continuously since late July (photo at left). However, female weevils will not lay their eggs inside the pecan until kernels start to fill. So with the kernel filling process underway, we applied our second weevil spray to our trees this week (August 23 & 24) to control both pecan weevil and stinkbugs.  For growers with high weevil populations be prepared to make a third weevil spray in early September.
    The kernel filling process also marks the time when squirrels start cutting open pecans in search of a meager meal of partially formed nut meat. This kind of squirrrel damage largely goes unnoticed by growers but we have begun to collect lots of nut fragments in drop cages set under native pecan trees (photo at right). Although, we might never claim complete victory over squirrels, we've been trapping squirrels in coni-bear traps since early summer to help reduce the resident squirrel population.