Mine are having the same issue and it's the first time I've grown them. They still appear to be growing fine and flowering lots so I'm not too worried.

I grew BK in 2014. It had leaf curl all season long. At the time I was a bit worried and did some search and found out that BK is prone to leaf curl. I should add that I had 3 more different variety in the same bed that were normal. Personally, I wouldn't worry about it.

Maybe other BK growers here can clarify that.

Sey

Thank you both. Won't worry about it then.

Most of my larger varieties have some degree of leaf curl, probably due to the stress of our rapid onset heat wave. BK has it more than some and less than other. Still growing and flowering, though. As long long as it's growing, I'm not worried about leaf curl.

BK is always my worst leaf curler. Doesn't seem to be anything other than cosmetic in my garden as they are still some of my most prolific and yummiest tomatoes.