Pecan leaf burst and first signs of pollination season

Kanza leaf burst, 26 Apr 2022

      Last week I was able to photograph several pecan cultivars as new spring growth emerged from long-dormant branches. As buds break, you should note the strong apical dominance of new shoot growth that is characteristic of pecan trees.  In the photo at right, new shoots and leaves sprout primarily from a cluster of terminal buds that developed as shoot growth slowed to a stop during the summer of last year.  Further down the stem, you will note that buds have broken open but seem to only produce male flowers or catkins. This is a consequence of apical dominance. The buds at the terminal of the branch break first and their growth sends a hormonal signal down the branch to suppress the development of  vegetative buds lower on the branch. 

    For sexually mature pecan trees, each primary bud on last year's shoot contains a central vegetative bud and two lateral male reproductive buds. Note that each male reproductive bud produces 3 catkins. As terminal growth continues to expand the hormonal signals become so strong that it causes central vegetative buds lower on the stem to abort from the tree. The catkins, however,  remain until they complete pollen shed later in May. 

Gardner, 26 Apr 2022

    As I moved through my orchard, I observed obvious differences between cultivars in terms of bud development and the appearance of catkins. Some trees appear to produce catkins well before new shoot growth. This occurs with protandrous pecan cultivars like Gardner (photo at left).

    Pecan trees have one of two flowering habits. Trees that release pollen before their female flowers become receptive, have a protandrous flowering habit. Trees that produce female flowers that are receptive to pollen before they release their own pollen are termed protogynous.  

   Over the years, I have also noted that the catkins on protandrous cultivars appear short and fat while catkins on protogynous cultivar are much longer and narrow.

Labette, 26 Apr 2022

    The photo at right is of a  Labette shoot and is typical of the early Spring appearance of a protogynous cultivar. Note how far the leaves have expanded in contrast to the Gardner shoot pictured above. Catkins on Labette have also emerged but they are not nearly a prominent as the catkins on Gardner at this point. However, note that even though Labette catkins are still enlarging they are already longer than Gardner catkins.

    During my tour of the orchard I noted two cultivars that had significantly later bud development.  Both Liberty and Hark are protandrous cultivars. Liberty appears to lag several days behind the leaf burst of other protandrous cultivars. In striking contrast, Hark leaf burst is far behind all other cultivars on my farm. Late leafing is a desirable cultivar characteristic for a pecan cultivar when grown in areas with a high risk of late Spring frosts.