Erica Pate, Fruit Crop Specialist, & Katie Goldenhar, Pathologist- Horticulture
Fungicide options for strawberry anthracnose control have become more limited for Ontario strawberry growers in recent years. In 2015 OMAFRA detected resistance to pyraclostrobin (FRAC group 11), the active ingredient in Cabrio and one of the active ingredients in Pristine (pyraclostrobin + boscalid) and Merivon (pyraclostrobin + fluxapyroxad). Additionally, a recent re-evaluation of the broad-spectrum fungicide captan resulted in the restricted entry interval (REI) for captan products increasing to 6 days. This longer REI means growers can no longer use captan during harvest for broad-spectrum disease control and resistance management. This is particularly challenging for day-neutral growers, who need to apply regular fungicide applications throughout the long day-neutral season for anthracnose control.
A better understanding of the presence of fungicide resistance in Ontario is important, and new and lower risk fungicides are needed for control and to help slow the development of resistance. Research in 2021 was targeted at addressing the challenges with anthracnose management and included fungicide resistance survey and fungicide efficacy screening.
Group 11 resistance testing
A plate dilution test was used in 2015 when resistance to pyraclostrobin, a FRAC group 11, was first confirmed in Ontario. This test is time-consuming and expensive, so only 5 farms were included in the original survey. Fortunately, there is now an alternative method for detecting anthracnose resistance. Anthracnose resistance to group 11 fungicides is associated with a known genetic mutation that confers complete resistance. This mutation is known as the G143A mutation, and has been identified in anthracnose in other regions, including the northeastern US. Detecting resistance using this genetic mutation is a faster and cheaper method and identifies resistance to all group 11 fungicides, not just pyraclostrobin. This method was used in the 2021 survey. Additionally, older isolates of Colletotrichum sp. collected from strawberries were screened for the G143A mutation.
In 2021, the Ontario berry team collected two samples from ten farms across the province. The G143A mutation was confirmed in every sample we collected. These results confirm that group 11 fungicides (as well as premixes containing a group 11) may not provide adequate control of strawberry anthracnose fruit rot, and that strawberry growers should not rely on group 11 fungicides for anthracnose control. FRAC group 11 products registered for anthracnose in strawberries includes Cabrio (11), Evito (11), Pristine (11+7), Merivon (11+7), Quadris Top (11+3) and Luna Sensation (11+7).
Some of these group 11 products provide control for other diseases. If using a group 11 product, make sure to include another effective product against anthracnose or include a group M fungicide when possible for broad spectrum disease control. Growers interested in having their farm surveyed for anthracnose resistance are encouraged to reach out to email@example.com
Fungicide efficacy testing
There are only two fungicides registered for anthracnose control that do not include a group 11: Switch (group 9+12) and Diplomat (group 19). New and lower risk fungicides are needed for control and to help slow the development of resistance. A fungicide efficacy study was established in 2021 at the Ontario Crops Research Centre- Simcoe to screen promising fungicides and biofungicides, to understand the control options available to growers and develop management recommendations.
Day-neutral strawberries cv. ‘Albion’ were planted in May in a randomized complete block design with 4 replications. Plants were inoculated with Colletotrichum nymphaeae spores on July 21 (after the first 2 fungicide applications). Fungicide treatments were applied on a 7 to 10-day schedule, starting at first flowering until September 7. The trial was harvested twice a week until September 7th.
- Control (no fungicide)
- Serifel (Bacillus amyloliquefaciens MBI 600) – FRAC BM02
- Problad (BLAD polypeptide) – FRAC BM01
- Diplomat (polyoxin D zinc salt) – FRAC 19
- Switch (fludioxonil + cyprodinil) – FRAC 9 + 12
- Cevya (mefentrifluconazole) – FRAC 3
- Mettle (tetraconazole) – FRAC 3
- Inspire (difenoconazole) – FRAC 3
- Fullback (flutriafol) – FRAC 3
- Sercadis (fluxapyroxad) – FRAC 7
This trial included non-group 11 active ingredients in two products registered for anthracnose control: difenoconazole (the other part of Quadris Top) and fluxapyroxad (the other part of Merivon). Diplomat and Switch are also registered for anthracnose control. The other products were promising potential products for anthracnose control.
DIPLOMAT 5 SC
SWITCH 62.5 WG
METTLE 125 ME
1 ns= no significant differences at a confidence level of 5%, Tukey’s HSD.
2Numbers in a column followed by the same letter are not significantly different at P = 0.05, Tukey’s HSD test.
Anthracnose pressure was low at the beginning of the season, and there were no significant differences between the fungicide treatments and the untreated control until August 10. However, disease pressure began to increase on August 10th and for the rest of the season Switch was consistently more effective than the other fungicide treatments and untreated control. When disease pressure was high Switch was the only effective product at reducing disease.
This project was funded by the Berry Growers of Ontario and the Canadian Agriculture Partnership. Thank you to the participating growers and OMAFRA summer students Ali Collingwood and Mathew Wake.