The problem is that you sprayed a product on your hydrangea without knowing
what was wrong with it. Are your hydrangeas sited in full sun? If they are,
they are probably just scortched a bit from too much sun. Some pesticides can
cause damage to certain plants. There should be information on the label
telling you what plants it should not be applied to. I dont want to sound like
a jerk, but you really should gather more information about a problem before
you apply any sort of chemical to your plants. You should also read the label
thouroughly so you know how to properly apply it and for saftey reasons. If I
felt like I was sick, I would go to the doctor and find out what was wrong with
me, rather than raid the medicine cabinet and eat a bunch of pills. The same
thing can be applied to the landscape, if you have a problem, take a sample to
your local nursery and someone should be able to help you. I hope your
hydrangea pulls through, but more than likely you just needed to water it.

Toad