Thursday, May 19, 2011

Pecan nut set

     We are half way through the pecan pollination season. Pecan pollen is still flying and there are still pistillate flowers that need to be pollinated. But at this point I'm seeing a pretty good nut set.
    In the photo at left, the stigmas of each female flower in the cluster has turned black indicating that the flower is no longer receptive to pollen. You can tell these flowers have been pollinated because the little nutlets have grown a little plumper. This enlargement of the ovary is in response to the germination of pollen and the growth of the pollen tube down the style towards the ovary. Fertilization, or the joining of male and female gametes inside the ovule will take place in a few weeks.

   This is also the time of year when you will be able to see weak pistillate flowers or non-pollinated flowers fall from the tree. In the photo at right, the red arrow points to a pistillate flower that dropping from the tree. Note how small the aborted flower is compared to the pollinated flowers still firmly attached.    
     If you are seeing a majority of pistillate flowers dropping off your trees, it is a good indication that the trees in your grove did not store sufficient energy last year to produce robust female flowers. Flooding, lack of nitrogen fertilizer, and premature defoliation can all lead to weak pistillate bloom.