Thursday, December 11, 2014

Mohawk: A precautionary tale

   We only have one Mohawk tree left growing at the Pecan Experiment Field (photo at right). Thirty 35 years ago, Mohawk was among the most popular cultivars being grafted in our region and we had dozens of Mohawk trees growing on the farm. At first look, Mohawk had everything a pecan grower would want--large nut size, thin shell, early ripening, and young trees that were both very precocious and productive. The story of Mohawk and the reasons this cultivar has been removed from pecan orchards all across the US is a tale that I always keep in mind as I evaluate new pecan cultivars.     

Mohawk pecans, 2014
    The story begins in 1946 when USDA pecan breeder, Louis Romberg, applied Mahan pollen to a Success pistillate flower. The resulting seed was germinated and grew into a tree that was later named Mohawk in 1965.
     At one time, the Success cultivar was the most popular cultivar grown in the Southeastern US. Success originated as a seedling tree planted in 1875 on a farm near Ocean Springs, MS.  This cultivar produces large thin-shelled nuts but as  the tree matures, nut production becomes erratic and kernel quality suffers terribly during "on" years. As plantings of Success increased across the Southeast, this cultivar became susceptible to pecan scab by 1931.
   Mahan is another cultivar that can trace its origins back to a Mississippi seedling pecan orchard. The tree originated from a seed planted in 1910 near Kosclusko, MS and was named after the nurseryman that first propagated the cultivar. Mahan is known for its very large nut size and long pointed nut shape. However, Mahan is now better known as a cultivar that never fully fills the inside of that large shell with kernel. Mahan is severely alternate bearing and often suffers cold damage following a heavy crop year.

     When Louis Romberg decided to cross Success with Mahan, he was hoping to produce a new pecan cultivar that would exhibit the best qualities of both parents--large nut size, precocious flowering, and heavy nut production. In the photo at right, a single Kanza nut is flanked by two Mohawk nuts. Mohawk is indeed one of the largest pecan cultivars that will ripen before frost in our area. As a young tree, Mohawk produces big beautiful nuts that are well filled and impressive to the consumer. But like both of its parents, serious problems arise when the tree reaches maturity (around 20 years old).    

    Mature Mohawk trees are similar to Success trees in that they frequently set too many nuts on the tree. This leads to poor kernel filling and the development of alternate bearing.  The photo at right illustrates the poor kernel filling of Mohawk as compared to a plump well-filled Kanza nut. Note how much space there is between the shell and kernel of the Mohawk. In addition, the kernel is fuzzy and the tips of the nut meat are shriveled. 
     Mohawk is also similar to Mahan in terms of susceptibility to cold injury. The vast majority of Mohawk trees that once grew on the research station were removed after winter cold killed trees to the ground. This type of extreme cold injury always occurred following a heavy crop year.
     As we grow and evaluate new cultivars, I always keep the story of Mohawk in the back of my mind. What may look like an outstanding new cultivar when a tree is young may turn out to be a real dud when the tree reaches maturity. The history of pecan cultivar development is littered with examples of pecans that fall apart at tree maturity. I'll name a few just off the top of my head: Shoshoni, Chickasaw, Creek, Dooley, Giles, Maramec, and Mohawk.