Fusarium infected cotton plants. (Photo by Robert Hutmacher)

• Information leaflet
• Identification videos
• General Fusarium information 
• UC IPM Cotton Pest Management Guidelines

Fusarium Wilt, caused by Fusarium oxysporum f. sp. vasinfectum, is a widespread disease causing damage to a wide host of crops. Until recently,  cotton was affected only through the association with root knot nematode. However with the emergence of Race 4, its presence has been felt throughout the San Joaquin Valley.

Current research efforts by USDA-Ag Research Service  and University of California Agricultural Experiment Station and Cooperative Extension  is working hard to find ways to manage this disease. Thus far, breeding for resistance and tolerance to the fungus is the most promising approach.

In order to use the variety best suited for your situation, knowledge of the infestation is required. This early period of plant development (emergence to first fruit) is a good time to watch for symptoms in the field. In seedlings and young plants, cotyledons and leaves wilt and drop, resulting in bare stems. In severe cases, plants die. In mildly affected plants, lower leaves develop symptoms but plants survive, but with reduced vigor. Look for breaks in the plant stand with associated dead or drying plants. Other symptoms include a general wilt, which is especially evident on warm days, and yellowing and necrosis of lower leaf margins. The vascular system of infected plants is brown. This is most apparent in the lower stem and upper taproot.

The UC CE Cotton Team has developed valuable information for identification and management of Fusarium Wilt Race 4. The UC CottonInfo website  provides current information including UCcottoninfo Channel on YouTube.  Bob Hutmacher and Brian Marsh have developed a video about “how to” look for disease symptoms, including which plant to sample which is very helpful.

COMMENTS ON THE DISEASE - From UC IPM Cotton Pest Management Guidelines

Four genotypes (called races) of Fusarium oxysporum f. sp. vasinfectum presently occur in California. Races 1, 3, and 8 are mildly virulent and cause few, if any, symptoms on cotton unless the plants are also infected with root knot nematodes. Race 1 is widely distributed in the San Joaquin Valley; races 3 and 8 are found in a limited number of fields in Tulare and Fresno counties. Race 4 is significantly more virulent and can cause severe symptoms on certain Pima varieties and mild to moderate symptoms on most Acala varieties. Seedlings of susceptible Pima varieties often die and resemble plant losses caused by damping-off fungi. Stand establishment in some fields is markedly reduced. The distribution of race 4 is not fully known, but it is becoming more common in Fresno, Tulare, Kings, and Kern counties.

     The fungus sustains itself on the outer surface of roots of many crops and weeds and survives indefinitely in soil. In addition, the pathogen is seed-borne in cotton, which accounts for long-distance spread, and is also spread whenever infested soil is transported on boots, farm equipment, in flood irrigation, etc.