Potato growers across Prince Edward Island are being told to watch for grey mold after spore counts in Queens County hit their highest level of the season this week.
The PEI Potato Agronomy team says counts reached 6,133 on August 26, up from just 18 two days earlier. The warning comes as most fields are still green and in the critical tuber bulking phase before harvest begins in September.
Ryan Barrett, research and agronomy specialist with the PEI Potato Board, says 10-foot strip yields are currently in the 250 to 300 hundredweight per acre range, which he calls quite encouraging for late August. But the sudden rise in grey mold pressure means growers should adjust their fungicide programs now.
Barrett recommends switching from mancozeb to chlorothalonil-based products such as Bravo or Echo for the next couple of weeks, especially on susceptible varieties. Vertisan offers good control of grey mold, while Miravis Duo can suppress it.
White mold is also starting to appear in some fields after about 10 days of wet weather. Sclerotinia mushrooms visible on the soil surface are a source of infection, the update notes.
There is some good news for growers. No late blight spores have been detected in PEI, New Brunswick, or the broader Eastern Canada and Northeast US region as of August 28. Aphid pressure also remains low, with just 38 aphids found in 37 samples province-wide on August 24, an average of about one per sample.
The advisory also includes cover crop recommendations for wireworm control. Brown mustard and buckwheat planted as fall cover crops have been shown to kill wireworms because of chemicals in their roots. However, tillage radish and oilseed radish have not been proven effective, as most brassicas have had the beneficial glucosinolates bred out of them.
According to the August 28 agronomy update, the province is coming off a tough 2025 season, when drought cut production by 16 per cent, the largest decrease in Canada. Inventory levels entering 2026 are 8 to 10 per cent below last year, making a strong finish to this year’s crop especially important for the industry.
