Because of the cold weather and freezing temperatures we have been experiencing, Sclerotinia sp. can be a problem in our cabbage, cauliflower, collards and other leafy brassicas.
I would recommend a 5-day rotation with following fungicides; (Fontelis; at labeled rate) and (Endura; at labeled rate).
Sclerotinia sclerotiorium usually begins on the lower stem, causing a watery soft rot followed by white, cottonlike growth. Black sclerotia, overwintering structures that give rise to the spore-producing apothecia, develop later. The disease is favored by cool, wet weather, which may result in a massive steamlike cloud of spores being spread throughout an area. The disease can infect cabbage from the seedling stage to maturity. On mature cabbage, the entire head is often covered with the white mycelium and black sclerotia, sometimes referred to as “raisin head.” The entire heads melt down, basically leaving a pile of sclerotia.