Weeds, pests, and disease

A MILD WINTER, WET SPRING, SURPRISE PESTS AND SOME USUAL SUSPECTS: 2024 was a typically atypical year in many respects. Here, Ontario Ministry of Agriculture, Food and Agribusiness (OMAFA) extension specialists share what stuck out to them – and what they’re thinking about ahead of spring 2025.

MILD WINTER CHALLENGES

A fairly mild winter in 2023/2024 ensured surface roots of some perennial weeds survived in greater numbers, making them tougher to control in the growing season, says Mike Cowbrough, the Ministry’s weed management specialist. Indeed, many weeds “came earlier and grew larger,” with control being even tougher in light of excessive moisture in some areas – west of London and Lambton County, for example.

“Some wild carrot reached a stage of tolerance that it didn’t matter what you threw at it,” says Cowbrough. At the time of writing [mid-October], he expressed hope that a continuation of mild autumn conditions would provide an opportunity to attack weeds when susceptible going into winter.

The proliferation of waterhemp is also continuing, albeit not necessarily quickly. Still, Cowbrough emphasizes that growers should be aware that it remains on the march. More unusual was a generally observed increase in pressure from grasses in the Lolium genus – ryegrass and bluegrass, for example.

“It’s a complicated genus with lots of hybridization,” Cowbrough says. Through a weed identification program operated in conjunction with his horticulture counterpart, Kristen Obeid, a high percentage of submitted Lolium grass samples were found to be glyphosate-resistant.

Cowbrough is unsure why this is happening, although possible sources of pressure could be turf blends – Lolium grasses are very common in turf blends – or seed spread from roadsides. But whether the grass problem of 2024 is a sign of things to come or a weird anomaly remains to be seen.

Problems aside, 2024 also reinforced some positive trends in weed control.

“I’m encouraged by the adoption of residual herbicide programs. Two-pass strategies in corn and soybeans, which maybe wasn’t there five or ten years ago. It’s minimizing risk,” Cowbrough says.

“I think there are some progressive people who dabble in entry-level cover crops like cereal rye or oats. I think that’s been helpful. I do see a little bit more diversity in terms of weed management.”

Getting on top of soil management is also critical, given the mild 2023-2024 winter. According to Colin Elgie, OMAFA field crop soil fertility specialist, the lack of winter frost and generally wet conditions holding until August made soil conditions “tight and challenging” for root development and nutrient uptake. A clear difference was observed between fields where more active soil management programs were implemented and those where planting occurred in less-than-ideal conditions – the latter showing earlier and more nutrient deficiency symptoms.

Elgie’s take-home message, consequently, is “the need to soil sample.” “Lately, I’ve been getting questions on where [and] how to cut back on fertilizer with crop prices dropping off and fertilizer prices staying relatively steady,” he says. “The short answer is, if you don’t have a soil test to start with, it’s all a guessing game. If you don’t soil test, you can’t complain about the price of fertilizer.”

MIXED PEST PRESSURE

As with some weed species, the mild winter also enabled greater survivability and earlier emergence for many insect pests. Tracey Baute, OMAFA’s field crop entomologist, says the volume and wide variety of cutworms pressuring crops in more northern regions early in the growing season was significant. With comparatively few boots on the ground to scout, tracking each species was a challenge.

“Part of the reason we learned about some of these cutworms was because of our collaboration with Manitoba and Quebec. The theme of all of this is our best efforts come from learning from our partners too,” says Baute.

Other standout cases include slugs and corn leaf aphids – the latter generating particularly high infestations in some corn fields in the province’s border regions.

On slugs, Baute says populations were frequently active all season despite some instances of hot, dry weather. They were particularly notable in no-till fields and those with cover crops. While expected, she says it is an unfortunate situation for those trying to build soil health.

“We need more integrated strategies,” she says, suggesting that plants that could lure slugs away or deter them from entering a crop might be a future remedy. “Can we limit the areas we have to control to make it more cost-effective? Just more predictability is needed. I think a lot of growers who had this problem were looking for answers, and we unfortunately didn’t have them right away. It’s going to be a lot of ground-truthing and testing ideas … A decent winter could help reduce our risk.“

“Unfortunately, we don’t necessarily see that as well as we used to, and even further north. It’s definitely enabling the extension of some pests. We really need to be more aware. Predictive tools would help, and ensuring we’re staying in touch within and outside of the province so we can respond more quickly.”

PATHOGENS MOVE QUICK

On the disease front, cereals specialist Joanna Follings says the past year served as a good reminder of the importance of timely scouting and fungicide application.

2024 started off well, with good winter cereal survivability and vigorous early growth. Nitrogen and sulfur application was a challenge, though, given spring rains and the rapid spread of stripe rust alarmed many cereal growers. Follings says it took just two weeks to spread province-wide.

“I think for growers that had resistant or more tolerant varieties, they had a wider window for [control] decision making,” she says. “It was a clear learning year in this regard. It was a reminder to all of us just how quickly stripe rust can move and how impactful it can be.”

Fusarium head blight was also identified as a common issue in winter wheat due to warm and humid conditions during pollination and grain fill. However, Follings says this did not appear to translate to high toxicity. She also echoes Baute’s assessment of how warmer winters are affecting cereal pests – particularly cereal leaf beetles.

“We had high insect populations, like cereal leaf beetle, in areas that historically haven’t needed control. That’s another reminder for us all to be out in our fields, so we’re always prepared for what comes next.”

For Albert Tenuta, OMAFA’s field crop pathologist, tar spot continues to illustrate how crop pathogens can still bring surprises. Tar spot, he says, was slow to develop in 2024 compared to previous years, suggesting it would be less of a problem. But when conditions turned favourable, it immediately took off.

“Diseases under favourable environmental conditions can still surprise me. Even after 33 years, I can still be surprised for the ability of those good pathogens, how quickly they can develop, and what an impact they can have on the plants themselves and yields,” says Tenuta. He adds that tar spot is now considered a risk at the regional level, not the local or field-specific level.

Other disease pressures were more routine – although tar spot has become a routine consideration across much of the province. Tenuta encourages growers to determine what risks they face in each field going into winter, address them where able, and select crop varieties with tolerance to the unique circumstances in which they will be planted.

“We all know there are certain fields that will have a white mould risk every year. Others will not,” says Tenuta. “Don’t just go by yield. Think about other impacts in terms of lodging, standability, disease resistance … I think the other thing is, we can’t predict the weather, but we can utilize new models, new forecasting tools, using technology to assist us in making better management decisions.”

DRONING ON

Weather can change on a dime – the regulatory environment, not so much.

For Jason Deveau, drones and the potential use of drones for spray applications is a perennial subject of interest and one which made minor advances in 2024.

Deveau is awaiting regulatory updates from Transport Canada, which might make it easier for drone pilots to acquire permission to operate. Currently, those wishing to operate a drone over 25 kilograms – the size you would need for spray applications – must apply for a Special Flight Operations Certificate every time they want to use it.

It’s a time-consuming and impractical process for both the applicant and Transport Canada, and Deveau says it is expected to be streamlined in December 2024.

Should operational regulations relax, though, it doesn’t mean drones spraying fertility and crop protection inputs will immediately fill the skies. Health Canada has yet to allow for the application of products by drone – with the exception of a mosquito-targeting larvicide, one fertility product, and one herbicide used primarily in forestry and road maintenance.

Even if drone-applied herbicides and fungicides were allowed tomorrow, many issues need to be addressed.

“We see planes and helicopters leaving these tell-tale green-brown stripes, and it suggests they need to spray a tighter pattern … Drones are no different,” he says, citing one challenge among many.

“A rotary drone operates in a unique way. It is more like an air blast sprayer in the sky. That factor alone has to be taken into account, good or bad … We’re still figuring these things out …we’re doing our best to give everybody some guidance here.” •