Oh darnit. Maybe it is leaf spot or smut. :-(
http://vvv.state.ct.us/caes/PlantPestHandbookFiles/pphC/pphcale.htm

It looks like it could be powdery mildew, but the variety that I'm growing this year appears to be naturally variagated.

It doesn't look like mildew to me. It looks more like insect damage.

barbe_wa-I would love to see pictures of a variegated calendula. I've never heard of one. Do you know the name?

F. DeBaggio

They did have a TON of black aphids on them, could that have caused insect damage?

As soon as I noticed them I cut off all the spent blooms, where most of them were. Then I sprayed the rest off with a hose. It seems to have worked- that was last Wed. and this weekend I only saw a few remaining and sprayed those off too.

Not likely to be damage from aphids, although some of it could be if they were feeding on the leaves. The serpentine damage looks like that of leaf miners. They leave trails like that as the nymph matures and burrows out of the leaf. Preventing the adults from laying their eggs by covering the plants early in the season is the only way to prevent the adult from laying eggs. Once the eggs are laid inside the leaf, there isn't much that can be done.
Other possible culprits for any other type of damage are: Leaf hoppers and thrips. It could also be damage from a type of true bug like the tarnished plant bug.

As long as the damage doesn't get too severe, your plants will likely survive.

F. DeBaggio

Here is a link that might be useful: Picture of Tarnished Plant Bug

Thanks. Leaf miners hmm. I think one of my chard plants did have leaf miner damage - is that the same bug that would attack both types of plants?

I cut the damaged leaves off the chard and it seems fine now, and none of my other chard plants were affected. But maybe they attacked the calendula instead!

This is only my 2nd year gardening so I've still got lots to learn.

Leaf miners will lay their eggs in the leaves of many different plants, including chard.

F. DeBaggio

F. DeBaggio - the variety I have that has spotted leaves is Zeolights. The spots are more yellow and smaller than what aubabe shows in the picture. I don't know if it is a characteristic of the variety or not, but the ones I grew last year had the same spots.

barbe_wa,
I looked up 'Zeolights' on several sites. No clear pictures of the foliage on any. No mention of it being variegated either. Any possibility of posting a picture of yours?

F. DeBaggio

I'm sorry but I've never mastered the art of adding photos, and I'm beginning to think I'm too old to learn. LOL. My grandson is visiting for a few days so if I can talk him into it, maybe he can help me out.

This is a picture of the Zeolight leaves.

barbe_wa-I'm afraid that is not variegation. It looks like a disease. Possibly leaf smut.

F. DeBaggio

It could be a disease, but like I said it was there on last year's plants, too, and doesn't seem to affect the flowering at all. The other varieties of calendula I've grown haven't had the same coloring.

I think mine may have had the same type of spots they have now last year too. Barbe yours are definitely more round and smaller than mine are though. I have to take another pic because it is actually much worse now. :-( I'm so bummed. Was going to use the flowers to make bath salts for Christmas like I did last year, now everyone is going to be dissapointed.

Well here's the latest pictures of my sad calendula plants.
At least yesterday I went to Bartram's Gardens in PA, which are the oldest botanical gardens in the country and noticed their calendula looked just like mine. At least I don't feel like such a terrible gardener now, if they can't even stop it! lol

The problem is likely due to mulching around the flowers. I have two separate beds. One is mulched with pine needles and the other has no mulch at all. Both beds receive the same amount of watering and were planted the same day and are from seeds I germinated in 4 inch pots before moving to the gardens. The bed with mulch has pale yellow blotches as described above while the non mulched flowers are larger, more flowers and no signs of blotches. It is either a soil moisture problem or an air circulation around the crown issue.