Monday, June 3, 2013

Natural crop load regulation during bloom

    Many pecan growers like to blame poor weather conditions during the pecan pollination season for a poor nut set. This happens whenever they see a developing nut cluster that has one or two flowers shriveled up and ready to drop off (red arrow points to 2 aborted flowers in the photo at right). Got to be poor pollination right? Wrong--its more often the case that the flowers aborting at this time of year were weak or poorly formed way back when the flower cluster was first created. Even if pollen lands and germinates on the stigma of a poorly formed pistillate flower, that flower is not strong enough to complete the fertilization process and will drop from the tree.
    In the photo at right, the red arrow points to a small, misshaped pistillate flower. This flower will never form a pecan and will eventually abort at the end of the pollination season. Note that this weak flower is located at the very terminal of the flower cluster. When a pecan tree develops pistillate flowers in the spring, the first flowers formed are found at the base of the flowering stalk (also known as the peduncle). As the flower cluster continues to grow, more pistillate flowers are formed along the peduncle. Eventually, the tree runs out of reproductive steam often resulting in the formation of small, weak flowers at the terminal of the flower cluster.
   The reproductive energy needed to create female flowers each spring is determined by the previous season's nut set and the tree's overall vigor. An excessive crop load one year is often followed by a year of weak pistillate flower formation (hence pecan's tendency towards alternate bearing). Drought, excessive flooding, lack of soil nutrients, insects and diseases can all put stress on a tree and reduce the strength of flower formation the following spring.
   So next time you start blaming poor pollination weather on your lack of pecan crop, think back to what happened last year. Did you do everything possible to ensure healthy tree growth?