Fusarium Yellows

Symptoms of Fusarium yellows usually begin to appear after plants are established. Infected plants turn yellow and are stunted. Some of the large roots may have a dark brown, water-soaked appearance. The water-conducting tissue (xylem) in the stem, crown, and root show a characteristic orange-brown discoloration resulting from infection by this soilborne, vascular fungus. In the later stages of infection, plants remain severely stunted and yellowed and may collapse. Invasion by secondary rot organisms results in soft rots and hollowed cavities in the plant crowns.

Note that aster yellows also causes similar yellowing and stunting; however, aster yellows usually causes severe petiole twisting and lacks the vascular discoloration caused by Fusarium yellows.

Once introduced into a field, this pathogen can survive for a number of years in the soil even in the absence of celery crops. The fungus can be moved about in infected plant residues and in infested soil. Symptoms are most severe on the summer celery crops because of warmer soil and air temperatures.

Until recently, Fusarium yellows in California was caused by a single pathogen, Fusarium oxysporum f. sp. apii race 2. However, a distinct new race, F. oxysporum f. sp. apii race 4, is now established in the state and can cause significant damage on celery cultivars bred to be resistant to race 2. Pathogenicity tests with differential cultivars or molecular tests are needed to identify which race is causing the disease in celery plants infected with this Fusarium. Depending on weather conditions (especially temperature), race 4 appears to be more aggressive on celery compared to race 2.

Note that this newer race 4 can also cause disease on cilantro.

• Avoid fields with known histories of the disease if possible.
• If the field is known to be infested with only race 2 of the pathogen, plant celery cultivars with race 2 resistance.
• Celery cultivars resistant to race 4 are not yet widely available.
• Avoid contaminating fields by preventing introduction of infested soil or crop residue.
• Growers who produce celery and cilantro should remember that race 4 infects both crops, which should influence crop rotation decisions.

Use cultural controls in a certified organic crop.