From my experience late blight affects the whole plant, not just leaves. It spreads fast and in few days the whole plants, leaves, and fruit, are done.

Check the soil if it is not to dry.

Thank you for the reply. The soil seems to be plenty moist. I have an automatic watering system hooked up to my earthboxes. I pulled out the sensor to make sure water is still flowing and it is. I also lifted up the mulch cover and the soil feels moist.

Could the temperature of the water dripping into the water reservoir cause this? The irrigation tubing is black and has to travel about 15-20 feet to get to the fill tube. Most of the tubing sits in the sun for at least 6-8 hours heating the water. I've never had issues in the past or with other vegetables that I have in Earthboxes (I have 6 others). Perhaps Cherokee Purple is more sensitive to the water temperature than my other tomatoes. Just a theory.

Is it possible to check the temperature of the water? Certainly, plants don't like to be watered with warm water. May be you could shade your irrigation tubing and the fill tube?

Or may be the soil in the earth boxes gets too warm anyhow? It could be beneficial to shade them, too.

I have other earthboxes that don't seem to mind the water temperature but I think I'll disconnect the Cherokee Purple from the watering system and water by hand for a few days with the colder water directly from the hose. If that works I'll report back.

I'm happy to know it's probably not late blight if you're saying that it works quickly and can impact the whole plant. So far the stems and fruit still look good.

Good luck!