Fusarium Wilt

Symptoms of Fusarium wilt in strawberries consist of wilting of foliage, plant stunting, and drying and death of older leaves, while the youngest leaves in the center of the plant often remain green and alive. Symptoms usually first appear well after plants are established. Plants bearing heavy fruit loads or subjected to stress often show the most severe symptoms. Plants can eventually collapse and die completely. When internal tissues of plant crowns are examined, vascular and cortical tissues are dark to orange-brown. Internal tissues of the main roots are typically not discolored.

Fusarium wilt is often most severe if the infected plant is subject to stresses due to weather extremes, deficiency or excess of water, poor soil conditions, or heavy fruit loads. Note that foliar dieback and internal crown discoloration symptoms are identical to those caused by Macrophomina crown rot. Therefore, confirmation of Fusarium wilt requires diagnostic procedures in a pathology lab. This soilborne fungus only attacks strawberry and will not cause disease on other crops. The fungus persists in the soil in the form of small survival structures called chlamydospores, which can last years in the soil in the absence of a host.

Select locations that do not have a history of Fusarium wilt. Preplant fumigation, which historically has been an important component of managing Verticillium wilt in strawberry fields, will also help control Fusarium. Fumigation will be most effective when crop residues have fully decomposed. Consequently, it is advisable to allow some time after incorporation before the fumigant is applied. Shank application of fumigants such as chloropicrin or chloropicrin plus 1,3 dichloropropene (Pic-Clor 60) applied at high rates under retentive film can control fungal pathogens, such Fusarium and Macrophomina (though only chloropicrin affects the fungus). Bed fumigation will not control pathogens in the untreated furrows.

Crop rotation with broccoli has been shown to help reduce Verticillium levels in the soil; the practice of crop rotation may also help manage Fusarium; it has not yet been thoroughly researched but is under current investigation.

Strawberry Cultivars

Field tests have shown that cultivars such as Fronteras, Portola, and San Andreas are resistant to Fusarium wilt, whereas Albion and Monterey are susceptible. Additional research is being conducted to develop new resistant cultivars.

Manage Stress

Manage the strawberry crop so as to reduce stress on the plants. Irrigate the crop as appropriate for the stage of development, current evapotranspiration requirement, and soil moisture levels. Control pests, especially mites, which can exert significant stress on strawberry plants.

Crop Rotation

Rotating strawberries with broccoli can significantly reduce levels of the Verticillium pathogen in the soil. While not yet tested with Fusarium, crop rotations may also be useful.

Select fields that do not have a history of Fusarium wilt. Plant resistant cultivars. Rotate with any non-strawberry crop or with crops, which have the capacity to suppress the pathogen. Avoid stressing the plants.

Drip fumigation of pre-plant fumigants may not effectively control soilborne pathogens in the entire bed; field research has demonstrated pathogen survival at the bed shoulders and in soil profiles deeper than 12 inches. Use of this application method should be considered carefully. Growers may improve fumigant distribution by using more than two drip lines per bed and by applying larger volumes of water to deliver the fumigants. Bed fumigation will not control these pathogens in the untreated furrows.