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 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 while 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.

The system algorithms are based on simulation models that are developed, tested and regularly modified by scientists in apple and grape-producing regions around the world. Spaying recommendations are updated every 30 minutes, based on local weather data. Using five system-compatible weather stations strategically located throughout the farm, Boonzaier will have the ability to micro-manage spray applications based on localized needs.

Manitree Fruit Farms, another apple grower near Blenheim, Ontario, is also experiencing  the need for increasingly complex protection planning due to the loss of some uses of group M fungicides and others.  

“I saw the writing on the wall in 2017 when I attended a minor use priority setting meeting in Ottawa,” recalls Brian Rideout, farm manager. “The trend in product registrations was moving away from broad-spectrum fungicides to single-site fungicides. And the alternatives were clearly in biologicals.”

This was a wake-up call for directing forward-looking crop protection strategies for his 400 acres of tree fruits – peaches, pears, tart cherries, apples – as well as vegetables. Located on the north shore of Lake Erie, he’s in a micro-climate that favours a multitude of crops.  Fortunately, given his role as chair of the crop protection section of the Ontario Fruit & Vegetable Growers’ Association (OFVGA), Rideout is a guy who questions the status quo and teases out the strands of complex problems.

In the last two years, PMRA has stipulated that many fungicide products must be used more sparingly in quantity, less frequently in timing and with more limits on re-entry and pre-harvest intervals. Mancozeb, for example, is now labelled for a 35-day re-entry interval for hand thinning and a 77-day pre-harvest interval. Backtracking from harvest date, it’s easy to see that application windows have become narrower.

“In the past, group M fungicides formed the backbone of our crop protection programs,” explains Rideout. “If you think of a pyramid, they have been the base because you could use them more than once and on more than one crop.”

Decreasing reliance on these products has a cascading effect on farm decisions, from warehouse inventory to the cost of more biological products and management of orchard workers. The bottom line ends up taking a double hit through an increase of about 10 per cent in upfront costs and through a higher risk of disease outbreaks.

As Rideout has determined through several years of on-farm trials, biologicals and chemistries together have their strengths.  But removing the umbrella control offered by group M fungicides invites the return of heretofore little-seen diseases such as sooty blotch, flyspeck and frog-eye leaf spot.  Clearly, no grower wants to apply expensive crop protection products from early spring to August only to find cosmetic blemishes on apple crops come harvest.

Given a reduced application window of group M fungicides occurring earlier in the season, apple growers need to develop new protection strategies for the rest of the summer. Like many other growers, Rideout uses Buran, a liquid formulation containing garlic extract to protect his harvest. It may not be the perfect bullet, but it helps.

For extension workers such as Katie Goldenhar, plant pathologist, OMAFRA, the relatively inexpensive group M fungicides have been a critical component of resistance management for single-site fungicides.  She agrees with Rideout that there’s an outstanding question. “How and when do we use the tools that are left to manage apple scab and summer diseases?”

 “In my opinion,” she continues “the reduction of uses and cancellations of group M products are leading the horticulture industry towards increased disease management costs: increased disease outbreaks, increased resistance to single-site fungicides and increased emergency use registrations.”

For Boonzaier, Rideout and many other growers, micro-management of each orchard block is fast becoming the new order - seven days a week, all season long.