that looks as if it has got too dry/hot. How many plants are affected?
the brown leaves will drop off but you should get new growth.

Did it get car exhaust on it?

I agree with SBG. It looks live a lack of water. If you have the energy, I would you go along the row and water with a can and then go back an hour later and repeat the action. Give it a week or so and if they are perking up, give them another treatment.