Yeah same thing here – slug grazing starting on lettuce pre-harvest. Is it a potassium deficiency? I’ve only read a bit about this, but it seems potassium demand is very low until a certain stage of development, and then becomes high.

I changed our lettuce planting to two rows in a bed, attempting to lower slug activity generally. More air between plants, easier to weed, easier to water, more nutrition. I’m planting less plants per bed but having much better efficiency, especially harvest and washing.