If downy mildew is the cause, following wet cool weather, a violet to gray mold will appear on the underside of leaves, directly under the yellowish area observed on the top surface. Affected areas on leaves die. Where disease is a persistent problem, plant resistant varieties and rotate with other crops. Where necessary, consider trying labelled garden sprays that contain a fixed copper. This can be a problem in fall crops.
High temperatures promote rapid development of symptoms.
The first sign that clubroot is present is a wilting of plants, especially where soil has been wettest. Pull a wilted plant to determine whether the wilting is caused by clubroot or insect grubs. Clubroot is characterized by distinct swellings on the tap and branch roots. Information provided is intended for consideration by the user, but is not intended to be a recommendation.