Charles, I’m in Somerset. My kale is rotated each year and I’ve never had a problem with it before, In fact it is usually too bountiful. The particular raised bed growing them this year was filled with well rotted horse manure several years back and last grew kale three years ago. I can only think that this bed is the nearest to a fence and my apple tree and perhaps the airflow is somewhat reduced here? I usually keep this bed for high summer stuff as it’s a little shadier, especially for lettuce, but every third year is my kale rotation. Perhaps no longer? By the way I mulched the bed last Autumn with my own compost.. The Taunton Deane kale grows in what was once a bed but is now a pathway (a blocked one of course!) and doesn’t seem to care a fig. Not had a problem with any other crop at all this year.
Eliza