Brown corky cracks and a hollow brown stem in my cauliflower curds

Brown corky patches on the curd with a hollow brown stem inside, on otherwise healthy plants in light soil, is most likely boron deficiency, a physiological disorder rather than a disease. Cauliflower has a high boron need and light or high pH soils are often short of it, which causes the hollow browned stem and corky curd. Confirm with a soil test, then correct it. For a standing crop a foliar spray of borax or a boron product can help if applied early, and for the longer term apply borax to the soil at the recommended low rate before the next crop. Be careful, boron is needed in tiny amounts and too much is toxic, so never overdose, follow the exact rate from your soil report. Also keep moisture steady since dry spells worsen the disorder. Get a soil test and the precise borax rate from your KVK before applying, as the safe and toxic levels are close together.