how do I save a tree that was sprayed with weed killer

I don't know, but I think it takes a whole lot of weed killer to kill a developed tree.

It you washed it off the leaves before it soaked in, that's good.

Don't trust me of course; I'll await more knowledgeable replies.

That sounds good. In addition to washing the leaves, avoid stressing it. In the summer, this usually just means keeping it watered, and a quick, cooling spray on the leaves. If it does look dead, give it till next spring to recover. It may fool you.

If it was something like Roundup, you have a chance if you water it off and hit it with some detergent in water within a few hours after spraying. If it was like Pqaraquat, or dicamba /24 D-that tree is probably toast. Both of those initiate an oidation process that the tree resperates itself to death.

Also, many sprays like Diuron , can kill from the root infiltration too.

Im not trying to be snotty but youve gotta pay way more attention, what if it were a pet watering can .Many of these herbicides, like roundup , Ally, or lasso, are often used as leaf hopper and moth pesticides also.