By: Erica Pate, Fruit Crop Specialist, OMAFA; Katie Goldenhar, Pathologist-Horticulture, OMAFA
Published March 2024
Botrytis grey mould is a widespread fungal disease affecting strawberries in both field and covered production in Ontario. Botrytis grey mould causes blooms to turn brown and causes fruit to develop small, firm brown lesions, which will eventually soften and develop a grey, fuzzy mould (Fig. 1). Infected berries eventually become dried and mummified. Botrytis grey mould can be caused by multiple species of Botrytis, with B. cinerea being the most dominant species infecting strawberry in eastern North America. Botrytis cinerea has a very large host range affecting over 200 crop hosts along with many weed species.
Recently, a new species of Botrytis, B. fragariae, was identified on strawberry in the United States including South Carolina, North Carolina, Virginia, Maryland, Georgia, and Ohio. Botrytis fragariae is host-specific to strawberry, only infecting strawberry plants, and seems to cause blossom blight, as opposed to B. cinerea which is detected more as fruit rot. Additionally, B. fragariae differs in fungicide susceptibility from B. cinerea, and fungicide resistance has been reported in both species, which could affect the level of disease control and management options.
Since B. fragariae has been identified in multiple regions with different growing conditions, it is likely that B. fragariae is present in other countries as well. It is important to learn more about this species and if it’s present in Ontario to inform management decisions. To date, this species has not been reported in Ontario or Canada. Current management practices were developed for B. cinerea, which may not be sufficient for B. fragariae.
Botrytis grey mould management includes multiple strategies, including physical, cultural, biological, and chemical control. Growers should keep rows narrow and encourage air flow. Avoiding excessive use of nitrogen will also help, as lush growth is more susceptible to infection. Chemical control includes regular fungicide applications before and during bloom, before an infection period. Single site fungicides are becoming more common in disease management programs. Make sure to reduce the risk of resistance by rotating fungicides with different modes of action. Broad spectrum fungicides have multiple modes of action and are excellent tools to include in your management program to reduce selection pressure on single site fungicides.
The OMAFRA berry team is conducting a survey this season to determine what Botrytis species are present in Ontario field and covered production strawberries, which will inform future management decisions. If you are interested in participating in this survey, please contact Erica Pate (erica.pate@ontario.ca), Cara McCreary (cara.mcreary@ontario.ca ) or Katie Goldenhar (katie.goldenhar@ontario.ca).
Figure 1 – Botrytis grey mould on Strawberry.
References
Amiri, A., A.I. Zuniga, and N.A. Peres. 2018. Prevalence of Botrytis cryptic species in strawberry nursery transplants and strawberry and blueberry commercial fields in the eastern United States. Plant Disease. 102: 398–404.
Dowling, M.D., M.-J. Hu, and G. Schnabel. 2017. Identification and characterization of Botrytis fragariae isolates on strawberry in the United States. Plant Disease. 101:1769–1773.
Rupp, S., C. Plesken, S. Rumsey, M. Dowling, G. Schnabel, R.W.S. Weber, and M. Hahn. 2017. Botrytis fragariae, a new species causing gray mold on strawberries, shows high frequencies of specific and efflux-based fungicide resistance. Appl. Environ. Microbiol. 83 (9)