Well.. Hopefully..
Thanks for all the comments.
I called the airport. Old VET's suggestion . Funny

never thought of that! Still waiting for a call back from the Dept. of agriculture

and tracking down the company that owns the property.
All those Governmental Depts. I called? No response! Nothing!
Got my info from some airport guy who answered the phone . He said he would sometimes shovel the stuff up they spilled and take it home.
Those of you who said
Fertilize get the last laugh. However I'm still following up with a few more people. Great news to me but I had rather them not spread anything on my property. Was happy to be wrong on this one.
Bottom line is someone spread a chemical all over my property. And basically I can do little about it.
I dealt with this a few years back when they were spraying to kill hardwoods and they assured me they knew the property line even though they were constantly circling overhead. Somehow I didn't trust their word. And I have lost an unusually large number of hundred year plus trees since. So many I could never find the time to harvest all of it, so it goes to waste. The value is hardly worth the harvest anyway. I just like having them and will never cut the mature ones. No worry, in hundred years I'll have those dead ones replaced like new.
I have thousands of feet in property line with the company's pine plantation and my property has a large stand of mature hardwoods. Getting to be a rarity in these parts due to pine timber value. These companies strive to eradicate hardwoods in their pines. They just kill'em and let'em lay. We once got a contract to log a large tract of recently poisoned hardwoods, they gave'em to us! We sold them as Tie timber.
I depend on spring water and grow vegetable crops so yeah it worried me when a plane flew over and rained down white pellets on my head. Might have never noticed had I not been standing there when the plane came directly overhead. I'm sure my chickens were eating the stuff too! Eggs for free for a week or so

..
The only interest of these timber companies is growing pines, they don't live here I do.
Once again thanks for all the serious replies and info. Great people on this forum.
Gotta get back to work.