Question: Why do my pecans turn black and watery and fall prematurely?

Answer: That is pecan scab, a fungal disease that is quite common in the eastern half of the state. It infects the pecans in early summer and causes them to start dropping by late August and into September. You should plant disease-resistant varieties. Apply a labeled fungicide in early summer and again with each successive spray you make into early fall. Get the complete spray schedule online by searching for "Homeowner Fruit and Nut Spray Schedule Texas A&M."
http://tcebookstore.org/pubinfo.cfm?pubid=206