Hi, neighbor. This is known as catfacing and has a number of causes.

For instance, catfacing can result from too much nitrogen, inconsistent soil moisture, cold temps while blossoms are forming, and exposure to pesticides. Of those reasons, cold spring temperatures are certainly a major reason -- or perhaps just the easiest to blame, as in my experience most catfacing is seen early in the season.

So essentially it has to do with the development, and the rate of development, of the fruit (something high nitrogen would have an obvious affect on). Or a combination of development and environment.

Catfacing is more common in beefsteak varieties like Cherokee Purple, so there seems to be a genetic component at least part of the time. Beefsteaks often form from double or extra-wide blossoms (known as fused blossoms or megablooms), and some people speculate an unusually-shaped blossom is more likely to catface.

I don't know if it really happens overnight. I always assume it happens while the fruit is too small to notice, or simply that I wasn't paying as much attention till the fruit got larger.

You can let them grow, but if there is a sizable split, it's probably best to pick them and let the plant spend its energy on more normal fruit.

And what I see are huge splits more than catfacing, which I can also see at the blossom end of the fruits and isn't the cause of the splits. Those splits are called horizontal splits, as opposed to radial and concentric splits and horizontal splits are caused by overwatering or XS rain when the cell wall and epidermis are at or almost at the maximum fruit size so any XS water taken up splits the fruits..

Are you near Asheville in the W part of the state? My brother is in that area and complains bitterly of all the diseases he sees there as compared what we see here farther north.

And Fletcher, just south of Asheville is the NCSU field station where so many wonderful varieties have been bred by Dr. Randy Gardner especially, whom I know well and have for many years. His Mountain series are very popular and of late his Mountain Magic F1 has been a real winner for me and many others.

Carolyn

when the cell wall and epidermis are at or almost at the maximum fruit size

Certainly you know infinitely more than I do about tomatoes, Carolyn. But to me those don't look at all like fruit which are at or nearing full size. Besides the general appearance of the fruit -- by which I think I mostly mean the texture of the skin -- consider the size of the sepals and the dried blossoms.

aisa didn't give a zone, but I'm taking "NC Mountains" literally -- in the mountains as opposed to simply surrounded by them as I am. So I assume aisa's a zone or two cooler than here, and I think that's probably too early for full-size Cherokee Purples.

USDA's 2012 Plant Hardiness map:
http://planthardiness.ars.usda.gov/PHZMWeb/#

Thanks very much for the responses! I'm just outside Hot Springs, NC, and that's zone 6b. These are not nearing full size...more the size of golf balls. It really did seem to happen overnight - I spend a couple hours each morning investigating and admiring so may have missed it one day, but not more. Don't use pesticides. I did find a yellow striped armyworm on the same plant but I'm thinking that didn't cause this. It could be overwatering. It hasn't rained in a few days and I throw a half gallon or more on them every 2 - 3 days. I'm going to check again for worms or bugs this evening. But it sure looks like some kind of splitting to me. Thank you again for your help. Last year I tried to grow tomatoes in both South Florida and in the high mountains of Colorado (7500 ft up)and failed both times....I'm still hoping for a success here. I'd choose a cherokee purple tomato over chocolate any day.

I can only see what I can see and I expect to see catfacing at the bottom of a fruit since that situation occurs when pollenization occurs during cool weather or the blossoms in some way are disturbed.

And I just don't see catfacing occuring half way up a fruit unless it's very severe catfacing.

Below is a link to some catface pictures and note that fruits of different sizes are involved as well as fruits in all stages of ripening and lots of immature green ones as well/

For anyone looking at Google images put your mouse pointer over each picture to confirm that what you're looking at is really catfacing b'c not all the pictures show that.

I looked at several pages of pictures and nowhere did I see any of the pronounced splitting that was shown in the picture put up by the original poster.

aisa, I had to chuckle a bit b'c first I talked about the NC mountains and then you brought up CO and I was there for several years, but at a slightly lower elevation than you mentioned, which is Denver, well, a couple of thousand feet lower actually, LOL, and yes, I grew tomatoes there, and that was in the late 60's through the 70's primarily b'c I moved back East to NYS in 1982.

Thank heavens. ( smile)

Ah well, it's seldom that there's total unanimity in diagnosing most of the problems presented by others.

And onward we go.

Carolyn

Here is a link that might be useful: Catfacing; Google images