Pecans - nuts moldy inside as soon as they fall from the tree.

I have five beautiful pecan trees. They are fairly old trees and produce exceptionally well as far as volume is concerned. I do not do anything special for them. The ones behind the house get whatever small amount of droppings that the birds leave around the ground and the one tree in front of the house is left alone.

The problem is that the nuts are not edible for the most part. Out of a 5 gallon bucket of pecans I might get a few handfuls that are edible and the rest have a brown moldy substance on them inside or are just black inside.

We do have a major problem with powdery mildew and other fungus/mildew issues here and I have read that can affect pecan trees --- but I really don't know what the problem is.

The trees are enormous so I'm not sure that there is anything I could actually do about it but I thought it couldn't hurt to ask.

I just picked up pecans tonight from an old grove where I work and the nuts are fine. These trees also recieve no supplemental watering or fertilizer.

Anyone have any ideas?

Not exactly related to your question, but have you provided any iron for the trees? That seems to be the cause of most the problems people have with pecans around here.
The reddish color on the shells is a good indication, the darker the better. Just sprinkle cast iron or steel filings/chips and cover with mulch inside the drip line (or bury a thin layer, if you're that ambitious), as they rust the tree will take up what it needs. A large tree will use up an amazing amount on each year's crop.
Any machine shop should be happy to get rid of some chips, just might need to wash them to get rid of cutting oils.

Joe, do you know if small pieces of iron, like cut pieces of concrete reinforcing wire, can be used to provide iron to trees?

Any iron or steel, with the possible exception of stainless steel, should provide the needed boost in iron levels. I would think the main factor is the size of the pieces. The smaller particles a given mass is broken into will determine the rate of oxidation and the rate of conversation to a usable form for the tree. Between working in machine shops and living near a 100+ year old cast iron foundry most of my life, I've never had a problem getting small chips to spread. I guess any rusting steel, no matter the size, is better than none.

A quick google for "iron deficiency in pecan" turned up quite a lot of info. My knowledge is just based on watching and listening to people older and wiser and watching the trees, so YMMV.

Edit to add; If you are keeping livestock under the pecans, I would think pieces of wire or rebar driven into the ground might be a way to avoid chickens or other animals ingesting the chips. I'm not sure if it would be a problem.