UGA Extension Pecan Specialist Dr. Lenny Wells has this to say about Pawnee nut drop:
We have seen a fairly large Pawnee drop over the last week. It is not uncommon for Pawnee to shed a few nuts this time of year but this year’s drop looks a little heavier in places. Still, I don’t think its anything much to worry about in most cases. Most of the Pawnee trees I have seen with a heavy drop under them still have a heavy crop on them. The drop probably helped them more than hurt them. The trees should be able to produce better quality and have a better chance of a return crop.
As the graph above shows, pecans undergo 4 separate fruit drops during the growing season, most of which are related to pollination problems. Pawnee is about a month ahead of most of our other varieties, so this drop would coincide with the 3rd drop in the graph above (which is based on Desirable). This drop occurs just before rapid fruit expansion and is due to the failure of the endosperm to develop properly. This drop is known to be accentuated by self-pollination. The low chill hours of this past winter and the resulting effect on budbreak (see Warm Winter and Pecans) could have affected cross pollination, leading to more self-pollination. If so, we may see a similar drop on other varieties in a few weeks.