Written by Katie Goldenhar, Pathologist – Horticulture, ONfruit November 11, 2026
Strawberries growers are faced with many diseases throughout the season including crown rots. In Ontario, crown & root rot pathogens include Phytophthora cactorum, Colletotrichum species (spp.), Neopestalotiopsis spp., Verticillium spp., Macrophomina phaseolina, Rhizoctonia solani, Pythium spp. and maybe…. Fusarium oxysporum. Fusarium oxysporum is a common soil dwelling fungus, often present in any sample of a root or crown but occasionally, it can be a primary pathogen.
Fusarium oxysporum can colonize host vascular tissue causing a blockage of water flow, leading to plant collapse. Symptoms of Fusarium wilt in strawberries include stunting, wilting and eventually plant death. Older leaves are often first to die back (Figure 1a), followed by full plant death. In the crown, red marbling of the tissue can be seen (Figure 1 b&c). Unlike Phytophthora, declining plants do not start in the lowest parts of the field but often in uneven patches in the field (Figure 2). Little is known about how this disease manifests in the northern North America, but it has been a major disease in California strawberries since 2008 (Koike et al., 2009), was reported in South Carolina (Williamson et al., 2012), and was most recently described in the northeastern United States (Westrick et al., 2026).
In two Ontario field cases (2023 & 2026), severe plant collapse was seen in late summer in Albion plantings. In both cases, the affected field was the second planting where there was no crop rotation between strawberry plantings, yet chloropicrin fumigation was applied after bed formation between plantings. In both cases, there were no other crown rot pathogens identified, and symptoms matched those of Fusarium wilt. Using a diagnostic lab is the primary way to diagnose a pathogen, especially crown rots, as the symptoms of these many pathogens are indistinguishable.
Figure 1. Crown rot suspected to be caused by Fusarium oxysporum cv. Albion
Fusarium oxysporum is a highly diverse fungal species, now classified as a species complex. We know that pathogenic strains are specific to hosts (and even parts of the host plant!), designated with a formae speciales (f. sp.). Fusarium oxysporum f. sp. fragariae (Fof) is the specialised pathogen causing Fusarium wilt in strawberries. There are genetic markers used to differentiate Fof from other Fusarium oxysporum strains but to ensure a pathogen isolated from a plant is pathogenic, one must inoculate the host and re-isolate the same pathogen, known as Koch’s postulates. To date, this has not been done in Ontario.
To make things even more complicated, there are also races of Fof. Races of a pathogen are classified on how they interact with host resistance gene(s). Fof is known to have 2 races that are differentiated by how they respond to genetic resistance in certain cultivars. Westrick et al (2026) described Fof strains from the eastern US as race 1. Based on many screening studies conducted in California, cultivars with Fof race 1 resistance include Fronteras, Portola, and San Andreas. Albion and Monterey are particularly susceptible to Fof. No resistance data for Fof is available on June-bearing cultivars.
Figure 2. Fields showing severe wilt in raised plastic beds of Albion.
There are genetic markers that allow for host specific identification of Fof – but many diagnostic labs only test to identify all F. oxysporum and this is a common soil organism with many non-pathogenic strains. A positive diagnostic report of just F. oxysporum does not confirm Fusarium wilt in the crop.
Repeated crops of any species is not a recommended agricultural practice. Pathogens are able to build up in the first crop and persist in crop debris, especially in strawberry crowns, as they have not been able to break down in the soil with the help of soil microorganisms. Studies in California have shown that strawberry crowns can harbour Fof deep in the soil and need multiple years to break down. Crop rotation away from any strawberries (even Fof resistant ones) of at least 3 years is recommended and is especially important in more opportunistic pathogens like Fusarium species.
Pre-plant fumigation is used when there is an economic incentive to plant in the same field to supress plant pathogens. Historically, methyl-bromide has provided the best control to suppress Fusarium wilt but is no longer used due to regulatory restrictions. A recent study from California (Henry et al., 2025) evaluated chloropicrin and 1,3-dichloropropene fumigation on their efficacy against Fusarium wilt and charcoal rot (Macrophomina phaseolina). Chloropicrin and 1,3-dichloropropene fumigation is the standard treatment used in California production. With drip applications, the fumigant was not consistently effective against Fof. The study suggests that using drip fumigation does not get deep enough to have efficacy against crowns in the soil, and these serve as the primary inoculum once the crop roots are stablished in the soil. Flat fumigation is more effective in general than bed fumigation as it treats more of the field but is typically cost prohibitive.
A promising alternative to chemical fumigation is steam sterilization. Practices such as anerobic soil disinfection or solarization are also alternatives to chemical fumigation but are less practical as prolonged heat is needed to achieve full effect and removes a field from production for a long duration. More info can be found here: Non-Fumigant Alternatives for Soil Disinfestation / Strawberry / Agriculture: Pest Management Guidelines / UC Statewide IPM Program (UC IPM)
Any pathogen that causes asymptomatic colonization (like Fof) is challenging to detect and control in a nursery and provides a pathway for long distance pathogen dispersal. Pastrana et al. (2019) showed that Fof can be transmitted from mother to daughter plants. Given the interconnected trade of strawberry plants in North America, it is reasonable to assume that the pathogen has been present in our region for many years.
There is still a lot we do not know about Fusarium wilt in strawberries, especially in our growing region. However, given that this pathogen has likely been present for many years, proper crop rotation seems particularly important to keep Fusarium wilt at bay in strawberries.
If you have questions or concerns about Fusarium wilt in Ontario strawberries, please contact katie.goldenhar@ontario.ca; 519-835-5792.
References
Henry, P. M., Hewavitharana, S., Holmes, G. J., Miller, D. B., Gillis, M., Stanghellini, M., & Bolda, M. P. (2025). Field Efficacy of 1,3-Dichloropropene and Chloropicrin on Disinfestation of Strawberry Crown Tissue Infected with Fusarium oxysporum f. sp. fragariae and Macrophomina phaseolina. Plant Health Progress, 26(3), 301–307. https://doi.org/10.1094/PHP-10-24-0103-RS
Koike, S. T., Kirkpatrick, S. C., & Gordon, T. R. (2009). Fusarium Wilt of Strawberry Caused by Fusarium oxysporum in California. Plant Disease, 93(10), 1077–1077. https://doi.org/10.1094/PDIS-93-10-1077A
Pastrana, A. M., Watson, D. C., & Gordon, T. R. (2019). Transmission of Fusarium oxysporum f. sp. fragariae Through Stolons in Strawberry Plants. Plant Disease, 103(6), 1249–1251. https://doi.org/10.1094/PDIS-08-18-1353-RE
Westrick, N. M., Marin, M. V., Henry, P. M., Hoffmann, M., & Peres, N. A. (2026). Emergence of Fusarium oxysporum f. sp. fragariae in the Eastern United States. Plant Disease, 110(9), 3640–3645. https://doi.org/10.1094/PDIS-10-25-2145-SR
Williamson M, Fernández-Ortuño D, Schnabel G. First Report of Fusarium Wilt of Strawberry Caused by Fusarium oxysporum in South Carolina. Plant Dis. 2012 Jun;96(6):911. https://doi.org/10.1094/PDIS-02-12-0164-PDN
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