Woad (Isatis tinctoria L.), a biennial or annual herbaceous plant in the family Brassicaceae, is used in traditional Chinese medicine with its root known as “Ban Lan Gen” and its leaves as “Da Qing Ye.” It is cultivated widely across China, with major production areas in Hebei, Heilongjiang, Shandong, Henan, Gansu, Anhui, and Jiangxi. The root is cylindrical, slightly twisted, with a light gray-yellow to light brown-yellow skin and a yellowish cross-section. It has a mild fragrance, initially sweet, followed by a bitter aftertaste. It is used to clear heat, detoxify, cool the blood, and relieve throat inflammation. Major diseases affecting woad include downy mildew, root rot, black spot, and viral diseases, with downy mildew, black spot, and root rot being particularly severe.