Heidi, agree with everyone it's saveable with copper.
Maybe Defender was already a dilute mixture, not enough "punch."
While it's never good when a new spear goes brown, the adjacent leaves look
so very healthy that it's likely not on its deathbed.
Zap it with copper, keep it dry.
Some people even drill a very small hole so the copper can drain away.
Heat will do it good.
If you get some, send it here too
Barb