The disease appears as faint, yellow spots on the leaves, and may show a white, fuzzy growth on the underside of the spots. These spots rapidly grow together and may kill the whole seedling. These symptoms usually appear only on the outer leaves of plants in the field. The fungus overwinters in the soil. To avoid an outbreak, it is best to keep the cold frame as dry and warm as possible, without inhibiting plant growth.
Infected plants appear stunted, sickly and yellow.
The leaves turn purple to brown, and the older leaves drop off. Scraping the lower stem will show streaks of discoloration. The fungus which causes cabbage yellows survives in the soil for many years and attacks the cabbage plants through the roots. The disease is favored by high soil temperature and high soil moisture. Fortunately there are many cabbage varieties very resistant to the cabbage yellows fungus.