I'm no expert but this link may help. I'm looking at Alternaria Leaf Spot and Septoria Leaf Spot.The second also affects tomatoes. With tomatoes I've found that the only thing that helps, for me, is rotating crops to a new spot.

Thanks for the response. It does look a lot like the Alternaria. This is planted in a bucket in new potting mix and peat moss, so it's not a matter of rotation. It doesn't say what could be used to halt the spread, unfortunately. Thanks again.

I once put too much manure in my tomato garden. The plants grew 12 feet tall, but still produced about the same amount of tomatoes. It grew so much that it outgrew the blight/Septoria problem as I call it. So I'm suggesting slightly over fertilizing. Don't go too far, just the right amount!

I've tried the copper spray which didn't work for me, I think because as soon as I apply it we get some rain. AND it's a preventative.

lilyd74 ... There are holes in the bucket for drainage but we have been having a LOT of rain here in NYC lately.

John D ... Thanks for the suggestion. I originally planted with some composted manure ... not too much ... but I fertilized with some high nitrogen fertilizer today.

Actually, browning leaves in cantaloupe is often indicative of overwatering. That's well understood. If you've had a lot of rain, and maybe a not-so-well draining bucket. that would do it. Overnight browning doesn't sound like fungal activity.

John D preventatives can still work to keep the rest of the plant healthy enough to produce fruit. Fert is of course also helpful with container plants. But given how much rain there has been lately, I lean more toward overwatering, even considering that the bucket has drainage. There's just a lot of water around this spring. My own cantaloupe hill is not thrilled with the moisture levels, and it's in a large bed. Containers are just more sensitive.

Thank you daninthedirt and lilyd74. The buckets do drain well, but we had 2 downpours today that flooded out some streets and similar weather is predicted into Friday! I guess were just at the mercy of Mother Nature. Notwithstanding, There are already a couple of little cukes growing on that plant so maybe it'll be okay. Thanks again for your input, all.