Fusarium Wilt

Fusarium wilt typically causes yellowing that begins on lower or older leaves, often more pronounced on one side of the plant or even one side of a single leaf, followed by progressive wilting that can be most visible during the heat of the day. Affected plants are frequently stunted and may die as the disease advances. Cutting a stem near the soil line usually reveals dark brown or reddish vascular discoloration, a key diagnostic sign of vascular wilt disease.

Fusarium oxysporum survives in soil for many years as thick-walled resting spores called chlamydospores, even in the absence of a host plant. The fungus infects through root tips and wounds, then colonizes the xylem, where its growth and the plant’s own defensive responses combine to restrict water transport.

Local spread occurs through infested soil, moving water, and contaminated tools or equipment. Longer-distance spread is mainly associated with infected transplants, seed, or the movement of infested soil between locations.

Fusarium oxysporum comprises many formae speciales: genetically distinct strains, each generally adapted to infect a specific host or narrow group of related hosts. Well-documented examples include tomato (forma specialis lycopersici), banana (forma specialis cubense, the cause of Panama disease), and cotton (forma specialis vasinfectum). Related Fusarium species and host-adapted strains cause comparable vascular wilt syndromes in other crops, including soybean.

Forma specialis

A physiological race of a fungal species defined by the specific host plants it can infect, rather than by visible structural differences.

Vascular wilt

A disease pattern in which a pathogen colonizes water-conducting tissue, restricting water movement and causing wilting.

Tomato is among the best-studied hosts of Fusarium wilt, and resistant varieties bred with specific resistance genes are widely available. Many other vegetable, fiber, and fruit crops have their own host-adapted forms of the fungus. Soybean and other legumes can also be affected by wilt-causing Fusarium species and formae speciales, though the specific strains involved differ from those affecting tomato.

• Tomato
• Soybean and other legumes
• Cotton
• Banana
• Melon and other cucurbits

• Previous presence of the pathogen in a field, due to its long persistence in soil
• Warm soil temperatures that favor fungal development
• Repeated planting of susceptible varieties in the same soil
• Movement of infested soil, water, or equipment between fields
• Root wounding from nematodes or cultivation
• Soil pH and fertility, which can influence disease severity in some host-pathogen combinations

Because the fungus can persist in soil for years, management relies primarily on prevention and host resistance rather than eradication.

• Plant resistant or tolerant varieties where available, often the single most effective tool
• Use certified disease-free seed and transplants
• Sanitize tools and equipment between fields
• Avoid moving infested soil or water between locations
• Rotate with non-host or less-susceptible crops as part of a broader strategy
• Monitor fields and diagnose symptomatic plants promptly