Managing wildfire smoke: impacts to crops and workers

Author: Natalie Hoidal. Originally published 2021, updated 2026.

Over the past few days, much of Minnesota has been blanketed by unhealthy concentrations of wildfire smoke from fires burning in Canada and northern Minnesota. How does the smoke impact you, and how does it impact your crops? 

First, it's worth acknowledging that wildfires have gotten worse in the US over the past few decades, which is attributed to historical forest management strategies and climate change. 

Impacts to plant health

When the sky is thick with smoke, it’s hard to imagine that there’s not an impact to crops. However, the impacts are a bit nuanced.

Access to light 

Wildfire smoke aerosols do create a shadier atmosphere, so you’d think that sunlight isn’t reaching plants as well. However, studies like Hemes et al. (2020) have found that wildfire smoke creates more diffuse radiation (aka light is scattered throughout the atmosphere), and plants can use this light more efficiently than direct solar radiation. Therefore, photosynthesis can actually increase in these conditions. However, this must be balanced with the impacts of other pollutants such as ozone.

Ozone damage  

Fires generate ozone and other aerosols. Plant stomata are pores on the leaf surface where gas exchange occurs, and while plants primarily intake CO2 and exhale oxygen, other gases also enter plants through their stomata. When high concentrations of ozone are present in the atmosphere, it can enter plants through their stomata, and can interfere with photosynthesis. These impacts can occur hundreds of miles from the area that’s actively burning (Yue & Unger, 2018).

The scale of these impacts differs between ecosystems: the uncertainty is based on ozone damage sensitivity, cloud cover, and aerosol properties. Symptoms of ozone injury vary by plant family but include interveinal chlorosis and necrosis (the leaf veins stay green, but the areas in between them turn yellow, and sometimes brown). Those areas can become bleached in some species. You might see irregular, tiny brown spots, almost like the damage you see from spider mites in cucumbers. 

The APS compendium series includes ozone in the chapters about abiotic stressors in most crops. In Brassicas, ozone exposure can cause chlorotic flecks. In cucurbits, it can cause chlorotic flecks, bleaching, stippling, and premature necrosis of leaves. Potatoes can respond with either chlorotic spots or darkly pigmented spots on the leaves. 

Ozone damage on a potato leaf. Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

Ozone damage on a watermelon leaf. Gerald Holmes, Strawberry Center, Cal Poly San Luis Obispo, Bugwood.org

 This article from Purdue shows additional examples of ozone injury on a variety of vegetable crops. 

These symptoms can easily be mistaken for other things like aging leaves, insect damage, or nutrient deficiencies.

Ash

In places like California and Australia where wildfires are much more common, people have cited problems with ash settling directly on crops, creating a physical barrier on the leaves, which prevents access to light. Grapes in California and Australia have had to be discarded after fires due to flavor changes, but this doesn’t happen all the time, and seems to be most common when wildfires are happening within a couple of miles of farms. If you're on the north shore where it's literally raining ash, these direct impacts are more likely than farms 100+ miles away from the fires.

A hazy, smoky morning in Minnesota. Photo: Natalie Hoidal

Human health and safety

While the potential impacts of smoke on vegetables are more speculative, the impacts on people are clear. Symptoms of smoke exposure include burning eyes, runny nose, chest pain, fatigue, coughing, difficulty breathing, and rapid heartbeat.

In 2024 we worked with the University of Minnesota's Doctorate in Nursing Practice program to develop air quality safety guidelines for farmers. These are research-based recommendations that can serve as a basis for decision-making on the farm. They are presented alongside heat safety recommendations, as we often experience poor air quality and heat at the same time. 

Review the air quality guidelines for farmers here, and keep a close eye on Minnesota's daily air quality forecast as you plan your farm work for the week. 

Sources

Hemes, K.S., J. Verfaillie, D.D. Baldocchi. (2020). Wildfire-smoke aerosols lead to increased light use efficiency among agricultural and restored wetland uses in California’s Central Valley. JGR Biogeosciences 125(2). DOI 10.1029/2019JG005380.

Keinath, A.P., Wintermantel, W.M. and Zitter, T.A., 2017. Compendium of cucurbit diseases and Pests (No. Ed. 2, pp. 228-pp).

Rimmer, S.R., Shattuck, V.I. and Buchwaldt, L., 2007. Compendium of brassica diseases (pp. viii+-117).

Shattock, R., 2002. Compendium of potato diseases, WR Stevenson.

Wotton, M., K. Logan, R. McAlpine. (2005). Climate change and the future fire environment Ontario: Fire occurrence and fire management impacts. Ontario Ministry of Natural Resources. Climate change research report; CCRR-01.

Yue, X., Unger, N. (2018). Fire air pollution reduces global terrestrial productivity. Nat Commun 9, 5413. https://doi.org/10.1038/s41467-018-07921-4