MARCH 2023
CELEBRATING 144 YEARS AS CANADA’S PREMIER HORTICULTURAL PUBLICATION
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Why more precision is required to protect apple crops
What to put in the spray tank? Decisions are harder than ever this spring as growers seek alternatives to group M fungicides, the ones with multi-site modes of action. Label rates are changing and the amount of active ingredient allowed per acre is diminishing. Manus Boonzaier, farm manager at Algoma Orchards, Newcastle, Ontario, has been testing his options for more than 1,500 acres of apples. Photo by Eric Forrest. KAREN DAVIDSON It’s a good practice to test your brakes on an icy road to prevent an emergency stop that sends you into the ditch. Such practical thinking is driving Manus Boonzaier’s crop protection program as changing regulations now impose new limits on group M fungicides, restrict others such as captan in 2022, and narrow mancozeb use in 2023. The 33-year-old farm manager has a lot at stake directing operations for more than 1,500 acres of high-density apples at Algoma Orchards near Newcastle, Ontario. “In 2022, I tried to play with some options,” says Boonzaier. “I’m still crossing my fingers that using half the labelled rates will get approved.” The Pest Management Regulatory Agency (PMRA) previously allowed eight applications of some group M fungicides per season, labelled as specified amounts of active ingredient per acre. That has now been changed to
just four per season. “We are hoping the manufacturers can get the label amended to four full rates or eight half rates per year,” says Boonzaier. “Eight half rates will help us a lot as we don’t use full rates when we use a group M with a SDHI product.” (SDHI refers to FRAC group 7 fungicides known as succinate dehydrogenase inhibitors.) Deciphering this regulatory labyrinth falls to Kristy Grigg- McGuffin, Horticulture IPM specialist for the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA). As she explains, “Currently, half rates are not permitted as per the label. To have half rates for mancozeb would require new data package submissions from the manufacturers. Crop protection companies are working with PMRA to change the current wording to allow flexibility in interpreting the maximum allowable amount so that half rates could be used if that’s common practice for a grower.” All of this to say that spray timing needs to be targeted with maximum efficiency. Most of Boonzaier’s group M
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fungicides will be employed from bloom through to petal fall. These products are intended to control apple scab, the most economically damaging disease, but also other diseases that affect quality. The fungus that causes apple scab overwinters as perithecia in dead apple leaves on the orchard floor. With spring rains, ascospores, the primary inoculum, are released from the perithecia. Apple trees become susceptible at the green tip stage which can occur as early as April in the Newcastle area. Understandably growers need to plan their spray programs very early in the year allowing for alternate plans that take into account changing weather scenarios. To become more flexible, Boonzaier subscribes to RIMpro, a British modelling system that forecasts ascospore release scenarios. Analyzing localized information on rainfall, leaf wetness, and relative humidity, RIMpro calculates the best time to spray for spores. Continued on page 3
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