I'm not sure either but this is the first year that I seem to be having the same problem. 4 of my tomato plants are getting the leaf curl and the bottom leaves look to be dry, even though I'm watering daily and they have straw mulch around them to keep in moisture. I forget what variety these are, but I bought all 4 of these in a ponypak container, so I guess I chalked it up to not being very healthy. My other four (medford tomatos) appear fine.