I am wondering how long an opened bottle of diazinon 25% is "good". I bought a huge bottle a few years ago and it says it should be used within 6 months of opening it. At a tablespoon or 2 per gallon I could have made hundreds of gallons of the stuff. Certainly more than I could have safely used on my lawn. What happens to diazinon as it sits? Does it become less effective as it ages? How long am I able to use it with the desired effect? Lastly, what do I do with the nearly full bottle of diazinon when it needs disposed of? Thanks a million for any help.