Hi, mine are like that too! I'm not sure what it is, but I saw a cucumber beetle chowing down on one the other day?? Maybe it's something else too though.

Hope someone else will chime in with what it is and how to stop it.

Maybe slugs?

Went out last night around 11 pm and saw the culprits - Asiatic beetles. Found this on Gardens Alive! and will rig up my light tonight:

"Remove the mulch temporarily and lay down wooden boards or old flat pieces of scrap wood on the soil around the plants being eaten. In the morning, go out with a five gallon bucket with a few inches of soapy water in the bottom and use a piece of flat metal to scrape the beetles (and any slugs cohabitating with them) into the soapy water. Never use gasoline, kerosene or other dangerous material for this chore; soapy water works perfectly well and you wonâÂÂt risk destroying your garden (and groundwater) if you stumble and spill the bucket.

And rig some long-term light traps outside the garden. Not too far away, but not in the center of your plantings either; no sense leading the pests to dinner. If you have a lamppost, wrap the area underneath the mantle in sticky paper and leave the light on at night for awhile."

Thanks, Jan. I found an Asian beetle on a bean plant the other day. I bet they're eating the Zinnias too...

Thanks, Jan. I found an Asian beetle on a bean plant the other day. I bet they're eating the Zinnias too...

Known enemy = plan of attack! I set up a lamp with a flood light and taped fly strips to the rim. Caught a few but they would end up dropping off onto the cardboard below. They were too heavy for the fly strip. Don't know if there is tackier tape out there. Had it set up about 15' from the plot.
When I saw it wasn't working I just went out with a bucket of water and hand picked those buggers. My husband checked on the plants about an hour later and said that there were markedly less beetles. I probably picked about 30. It was hard to stop!

Better to hand pick. Sticky traps like those kill other bugs that may be beneficial to your garden.