The first symptoms of wilt are yellowing and browning of the leaves, which die from the base of the plant upwards. Infected plants are stunted and often fail to produce flowers. The entire plant may wilt and die. The fungus is soil-borne, and enters the plant through the roots, later invading the vessels of the stem and cutting off the water supply. Remove and destroy all infected plant material.
Ultimate control lies with purchasing certified disease-free plants and strict sanitation locally.
It is best to use resistant varieties. If Fusarium has been a problem, increase the pH of the soil to 6.5 7.0. This disease is caused by the fungus Erysiphe cichoracearum . The leaves are covered with a whitish, ash-gray powdery growth. The spores require a very moist atmosphere in which to germinate and spread the infection.