Head rot is an airborne disease, so there's no way to avoid it. If your plant is susceptible, it will get it. The risk factors are heat and humidity when the head is maturing.
However, check out the red cabbage and the green kale -- they're not infected. That's probably because the green kale was planted as seed, not as seedlings, so it hasn't been maturing in the humidity. Either that, or the green kale just isn't as susceptible.
The red cabbage isn't affected probably because it's late maturing. Only one of the heads is close to being mature.
If you plan on growing kale next year, consider planting one of the sturdy green varieties, and start it in the garden from seed. If you do grow red kale, grow it from seed. You can plant kale up to July 1 for a fall harvest.
Also plant your kale so that it has lots of air. Avoid crowding it or placing it in the shade of another plant.
In the meantime, consider harvesting your red kale while most of it's still edible. Cook kale the way you'd cook broccoli (e.g., steamed 3 minutes for salads, stirfried with other veggies, cooked into quiches and frittatas, etc.). Dutch, Polish, and German recipes for traditional kale dishes are available on the web. And there are even recipes for making "kale chips."