Shelf life of products with 2-4 D
How long is weed killler effective if it is stored in a garage over multiple hot summers in Texas?
Certified GKH Gardening Expert
This is, typically, good for anywhere between 2 to 8 years depending on the care of it. Since it has been hot, I would assume that it is on the lower end of that, since it has been exposed to heat. There would be not extra harm in trying it to see if it works still.