Scab on 'Mandan' pecan

    The cultivar release notes published when Mandan was first made available to the public claimed that nuts produced by this tree are resistant to pecan scab. Although not extremely susceptible to scab we have found Mandan shucks infected with the disease.
    This past season we applied a fungicide three times to our Mandan trees during the months of June and July. For the most part, we have kept the shucks mostly clean with only a few small scab lesions appearing by late summer (photo at right).

   However, where we didn't get good fungicide coverage on the nuts, I found several clusters of Mandan nuts covered with scab lesions (photo at left). Mandan also seems to be susceptible to powdery mildew.
    While taking this photo of scabby nuts, I found a crab spider resting on one of the nuts. Crab spiders are a common insect predator in pecan tree canopies with female spiders often hiding their eggs at the base of nut clusters.

Mandan: Notes on nut quality

Mandan, 2013 Crop

    Mandan was released by the USDA based on the fact that it produces a large pecan that ripens early. However, ever since I first saw nut samples produced by this cultivar, I have not been a fan.  The nuts produced by Mandan are indeed large (photo at right) but notice that the nut appears narrow when viewed suture side up (nut on left)  compared to the width of the nut when viewed 90 degrees from the suture (nut on right). This shell geometry is always associated with pecans that produce kernels with narrow dorsal groves.

    Our  Mandan nuts averaged 7.65 g/nut and 58.64% kernel this year. These numbers look impressive but a quick look at the kernels makes you wonder how nutmeats that look so shriveled produce such high percent kernel. The upper side of the kernels often appear wrinkled and veiny. The narrow dorsal groves often traps shell packing material. The back side of every kernel was hollow and depressed indicating a less than perfect kernel fill. Overall, the kernels produced by Mandan were not up to my standards for exceptional kernel quality. When it comes to quality pecan kernels, Kanza and Pawnee are far superior.      

Scab on Mandan

  

Scab lesions on Mandan pecans

     Mandan is one of the newer pecan cultivars developed by the USDA . Because it produces large, early ripening nuts, it has created considerable interest among northern pecan growers. When its was released, Mandan was promoted  having "good scab resistance".  This is the third year we have fruited Mandan but this summer has been the first time our Mandan trees have been exposed to conditions favorable for the spread of pecan scab.
   Once the rains kicked in this summer, I was able to find scab lesions on our Mandan nuts (photo above). Finding that Mandan is susceptible to scab does not surprise me.  I found scab lesions on Mandan twigs shortly after we grafted this cultivar into our orchard back in 2011. To me, Mandan seems to be similar to Pawnee in terms of susceptibility to pecan scab.
   Scab can be controlled on Mandan with a fungicide program but the kernel quality issues I've seen with this cultivar will prevent me from propagating additional trees.