Flowering type noticeable at bud break

    Pecan trees have one of two flowering habits. Those trees that shed pollen before their pistillate flowers become receptive to pollen are said to have protandrous flowering (also known as type 1 flowering). Pecan trees that shed their pollen late in the pollination season and produce receptive pistillate flowers before they shed pollen are called protogynous ( also known as type 2 flowering). Having catkins and pistillate flowers mature at different times on a tree is nature's way to ensure cross pollination.
    You can easily see which flowering habit a cultivar will have by close observation of bud break. Here is a photo of emerging new growth from two pecan cultivars: Oswego and USDA 75-8-5. Oswego is protogynous while USDA 75-8-5 is protandrous. Note that the catkins on the protandrous cultivar are already well developed while  catkins on the protogynous cultivar are barely showing (red arrow points to emerging catkins).
    Besides watching for the time of pollen shed, you will note that catkins produced by protandrous cultivars are short and fat while the catkins produced by protogynous cultivars are long and narrow.