Will it affect herbicide efficacy? Is it safe or effective to spray in smoky conditions? Could it influence inversions?

The short answer: it’s complicated — but there are some educated guesses and early-stage research that can help.

Don’t delay spraying

Tom Wolf, a longtime spray expert and contributor to Sprayers101.com, says while there’s no direct research on the impact of wildfire smoke on herbicide application, some inferences can be drawn based on how smoke affects plant growth, solar radiation and atmospheric conditions.

“It is difficult to say, because we don’t have very specific information on the effect of smoke on the spray operation itself,” Wolf says. “We do have some information on plant growth, so we can infer a few things about herbicide performance that might be a result of its effect on plant growth.”

One of the key concerns, he says, is that wildfire smoke may reduce thermal turbulence during the day. This turbulence plays an important role in spraying by helping droplets settle into the canopy and by dispersing them to minimize drift. Smoke blocks sunlight, reducing surface heating and weakening the air mixing that creates thermal turbulence.

“So it’s possible that if drift occurs, it will likely have a longer reach,” he says.

On the other hand, the effect of smoke at night might actually be positive. Wolf says it’s possible smoke could suppress nighttime inversions by trapping heat near the surface. If that happens, it could delay the onset or reduce the severity of an inversion.

Beyond air movement, smoke can also affect the plants themselves — potentially impacting uptake and efficacy. Smoke reduces photosynthesis in plants and overall plant growth, and Wolf points out that vigorous plant growth helps herbicides move through the plant effectively.

“If the plant hurts, then herbicide translocation hurts,” he says.

Another concern is atmospheric humidity. Smoke particles absorb moisture from the air, which can dry the atmosphere — not ideal for spraying. It means the spray droplets arrive a little smaller, and more prone to drift.

A drier atmosphere can also hinder herbicide uptake. Sprays are most effective when droplets remain wet on the leaf surface, since the herbicide is absorbed more efficiently during that time.

“We really want drops to stay wet as long as possible,” Wolf says.

Still, he emphasizes, any negative effects from smoke are likely to be minor compared to the risks of delaying a spray. Waiting too long can allow weeds to get ahead of the crop and start causing yield losses.

Sunlight dependency

As for specific herbicides that may be affected, Manitoba Agriculture weed specialist Kim Brown says smoke-related conditions — particularly, reduction in sunlight — may affect the performance of some light-activated herbicides.

“The main one I think of is Liberty,” she says. “We know that it requires a good dose of sunlight to really be effective.”

That’s because Liberty (glufosinate) relies on photosynthetic activity in the plant to facilitate uptake and injury. “We might see reduced activity from Liberty if it’s cloudy or smoky,” Brown says, though she emphasizes there hasn’t been formal study of this in smoky conditions specifically.

Another product that might be affected is Reglone (diquat), used for crop desiccation. “That’s another one where we know sunlight plays a role,” she says.

Brown also echoes Wolf’s point that inversions — the calm, cool conditions that trap spray droplets close to the ground and increase drift risk — could be influenced by smoke.

“Reduced sunlight could delay the warming of the ground in the morning, which may extend the inversion period,” she says. “But we really don’t know enough yet to quantify how often or how significantly that happens.”

Limited research, some emerging data

The lack of data is a recurring theme in talking about the effects of wildfire smoke on cropping systems. While most experts agree smoke is unlikely to affect yields in a major way, they also caution that very little research has been done.

While formal research remains sparse, growing recognition that wildfire smoke may be a recurring issue is beginning to drive more scientific attention.

A 2024 PhD dissertation from Kansas State University used satellite data and historical yield records to show that wildfire smoke exposure has been reducing soybean yields in parts of the U.S. northern Plains.

That’s certainly the expected result: less sunlight means less photosynthesis, which can lead to lower yields. But not all early findings point in the same direction.

Research out of Purdue University in Indiana found wildfire smoke may actually have a small benefit for corn under certain conditions.

The study looked closely at how smoke affects solar radiation — and what that means for corn.

“Smoke reflects sunlight,” says Dan Quinn, assistant professor of agronomy and extension corn specialist at Purdue. “But it also scatters it, and that can actually help tall crops like corn.”

Speaking at CropConnect in Winnipeg last year, Quinn explained that scattered, or diffused, light penetrates the corn canopy more deeply, which can boost photosynthesis in the lower leaves. That slight cooling can also reduce crop stress during extreme heat.

While he says it’s difficult to pin down the yield impact exactly, Quinn suspects the 2023 smoke in Indiana may have been a net benefit.

“It likely resulted in a net positive for corn grown in the state,” he said, but added that same benefit could be specific to corn because it’s a tall crop with a deep canopy.

A grey area

For now, there’s more inference than certainty around the effects of wildfire smoke on Prairie farming. With research still in early stages, farmers will have to make decisions based on best practices and observation rather than established data.

So, for now, Wolf’s advice still holds: don’t wait to spray.

Wildfire smoke poses a mounting threat to public health, even when fires aren’t visible nearby, according to the Manitoba Lung Association (MLA).

The association warns that breathing wildfire smoke can cause both immediate and lasting lung damage, with seniors, children, outdoor workers, pregnant individuals and people with respiratory conditions like asthma and COPD (chronic obstructive pulmonary disease) more at risk.

Less risk, though, does not mean no risk. A press release sent out by the organization May 30 noted that smoke can harm anyone’s lungs regardless of age or health status.

“Wildfire smoke doesn’t respect boundaries — and it doesn’t take a visible fire to put your lungs at risk,” said Juliette Mucha, president and chief executive officer of the MLA. “We’re urging Manitobans to act now, not later. Know the risks, check the air quality health index, and protect your lungs before smoke becomes a crisis.”

Health risks for farmers and outdoor workers

When smoke is heavy, farmers and others in the agricultural industry who often work outside should wear properly fitted N95 masks or P100 respirators, which provide protection against fine particulate matter in smoke.

Cloth and surgical masks are ineffective against wildfire smoke, the lung association says. Vehicle occupants should also use the recirculate vent feature while driving.

Protecting livestock from smoke exposure

Livestock and large animals suffer similar smoke effects as humans.

“Prolonged wildfire smoke exposure may cause respiratory irritation, inflammation and negatively impact cattle health and production,” said Dr. Leigh Rosengren, the Canadian Cattle Association’s chief veterinary officer. “Producers in affected areas are encouraged to monitor animals closely and contact their veterinarian if they have concerns.”

Like humans, animals can suffer immediate and long-term effects from breathing wildfire smoke, including eye and respiratory tract irritation that makes breathing difficult, according to U.S. Environmental Protection Agency (EPA) guidelines. Animals with existing heart or lung conditions and older animals face heightened risks during periods of poor air quality.

Caring for livestock during smoke events

The EPA also advises that farmers should limit strenuous activities for their animals during smoke episodes and provide plenty of fresh water near feeding areas. Animal health experts also suggest using low-dust or dust-free feeds and sprinkling or misting livestock holding areas to reduce dust exposure.

For outdoor birds, owners should consider moving them to less smoky environments such as garages or basements when air quality deteriorates.

Livestock require four to six weeks to fully recover from smoky conditions before resuming strenuous activity, the guidelines say.

Emergency evacuation planning

Preparation before wildfire season is another key part of livestock safety, said the EPA. Farmers need to identify evacuation locations and maintain good barn and field conditions to reduce fire danger for horses and other livestock.

Proper record keeping becomes essential during emergencies, backed up by animal-specific identification through ear tags, tattoos, electronic microchips or brands. Farmers should maintain current photographs of high-value animals like horses and keep detailed lists of species, numbers and locations with evacuation supplies.

Evacuation kits should contain seven to 10 days’ worth of feed, supplements and water, along with blankets, halters, leads, water buckets and manure forks. Vaccination records, medical records and proof of ownership should be easily on hand.

Farmers should also identify trailer resources and train livestock to load properly. Multiple evacuation routes should be planned, with temporary shelter arrangements made at local fairgrounds, stockyards or equestrian centers.

When evacuation isn’t possible

If they can’t evacuate, farmers should move animals to preselected, cleared areas with lower fire risk. Gates should be opened and fences cut to allow animal movement. Neighbours and first responders should be notified about animal locations, the guidelines say.

Food and water supplies for 48 to 72 hours must be left behind. Automatic watering systems may fail during emergencies, the document warns farmers.

Property owners must not return until officials declare it safe to do so.

The guidelines also emphasize that human safety remains the top priority during wildfire evacuations, with animal welfare considerations secondary to protecting farmers and their families.