Your Dill has put up a flower stalk so it's now on its way out, I'm afraid. Dill is a short lived annual and the best way to have a constant supply is to sow at intervals throughout the season. Your best bet now is to use yours up asap and start some more. I would also grow it in a plastic pot (inside a clay pot if you prefer the appearance) and give it a drip saucer. Terracotta with no saucer is going to dry out very fast through draining and evaporation.

Thank you! I have the herbs in this standing planter to keep my dogs away. Plus I'm a renter so I can't really plant directly in the ground. I'll consider the plastic inside the terracotta though. That definitely would explain why my plants seem to be thirsty all the time. Thanks for your advice!

Dill freezes really well if you want to preserve as much of it as you can. I just cut whole sections and put them in a freezer bag. Then you can replace the plant and get a second harvest.

It looks like you've got powdery mildew. Google it and compare the images to your plant to be sure. I've never dealt with it, but I've read that spraying the leaves with diluted milk (milk 1:10 water) is sometimes effective. Like floral said, though, it's going to go to seed soon anyway.