Fusarium Wilt

CAUSAL AGENT

Fusarium wilt in cucurbits is caused by Fusarium oxysporum (fs. spp. cucuerinum, cucurbitae, melonis, and niveum). The specific strains are adapted to specific hosts.

SYMPTOMS

Wilting is the primary symptom of infection by F. oxysporum. Wilting does not occur until several weeks after infection; therefore, young plants can unknowingly be infected. Sometimes, wilting only occurs on one side or portion of the host. Initially, plants may recover in cooler evening temperatures. Older foliage becomes chlorotic and dies. Over time, and especially with hot temperatures, permanent wilting sets, in followed by plant death and sometimes vascular discoloration.

DISEASE CYCLE

Fusarium oxysporum can occur in most soil types across Utah. It survives in the soil or plant residue for multiple years as mycelium or thick-walled resting spores called chlamydospores without a host plant. It may also be present in soil debris on greenhouse benches, irrigation pipes, mechanical equipment, and other field supplies. Fusarium wilt is a disease of warm, wet conditions. In these circumstances, chlamydospores germinate and produce infection hyphae. These hyphae penetrate the root cortex or may enter through wounded or damaged roots. Hyphae then invade the xylem (vascular) tissue, where the pathogen repeatedly sporulates and grows hyphae throughout the plant, essentially clogging the vascular system. If plant defenses cannot prevent the spreading of the pathogen, the plant wilts and dies. Upon plant death, the fungus spreads and grows on the outer, decayed areas of the plant, forming masses of mycelium and subsequent chlamydospores for longterm survival.

Management

Both diseases are very difficult to control due to the production of the long-term survival structures in the soil. 

• Use resistant varieties when available. Resistant tomato varieties are available for Verticillium race 1 but not race 2, and for Fusarium oxysporum races 1, 2, and 3.
• Plant on raised beds for better water drainage.