Disease Management

Pumpkin Vine Fusarium

Fusarium Diseases of Cucurbits

Species of Fusarium can cause three distinct disease syndromes on cucurbits: vascular wilt, root and stem rot (damping-off), and crown and fruit rot.

 Different formae speciales of the Fusarium oxysporum fungus cause vascular wilts of cucumber (cucumerinum), melon (melonis), and watermelon (niveum). Squash can be infected by the watermelon pathogen. Symptoms of the disease can vary with plant age, host, environmental conditions, amount of pathogen in the soil, and the aggressiveness of the pathogen strains. Seedlings can develop damping-off and lower stem infections. Vascular wilt symptoms first appear as dull-green coloring of the foliage, yellowing of older leaves, and temporary wilting. Symptoms may initially occur on one side of the plant. As the disease develops, wilt may affect all leaves and shoots, plants become stunted and suffer from poor growth. Leaves eventually become necrotic and dry up, and vines collapse and die.

A distinct F. oxysporum pathogen causes root and stem rot (radicis-cucumerinum).

Symptoms occur as tan to brown lesions on the plant crown and upper roots. Infected plants grow poorly and may collapse.

Crown and fruit rot is primarily a problem on squash and pumpkin and can severely affect the quality of fruit. The pathogen, Fusarium solani f. sp. cucurbitae, infects the crown and root tissues of seedlings and older plants causing water-soaked lesions near or below the soil line on crowns and upper roots. Lesions may darken, girdle the plants and cause wilt and plant death. Surfaces of fruit that are in contact with the soil develop tan to brown, firm, dry and sunken lesions. Lesions may occur in concentric rings and remain firm unless invaded by secondary organisms.

All Fusarium pathogens are seed and soil borne. The vascular wilt pathogens can persist in the soil for long periods as saprobes or chlamydospores. Wilt diseases are more severe in sandy, porous soils with high nitrogen content and acidic pH. Fusarium diseases increase whenever plants are stressed by unfavorable growing condition or heavy fruit set.

Management:

• Plant resistant cultivars. Because pathogens exist in numerous races, knowledge of the prevailing races is needed.
• Rotate out of cucurbits for 3-4 years.
• Start with certified, disease-free seed.
• Avoid moving contaminated soil by equipment or water.
• Soil fumigation is initially effective, but soils are quickly recolonized.