Smoke from wildfires has been more prevalent in recent years, and this year is no exception. Haze from fires is coming into Ohio and other states in the northern region as our crops approach or already are in early reproductive growth stages (Figure 1). Haze at the end of June and early July in 2023 had minimal effects on crop yields (state record yields were observed for both corn and soybeans in 2023). Although we are about 3-4 weeks ahead developmentally this year compared to 2023, we would still anticipate yield effects will be small from this year’s conditions.
The major concern with haze comes from overall reductions in light availability to crops. Reports have shown that a reduced light intensity of 15% did not affect corn yield, though yield losses have been evident when sustained reduced light availability of 30-50% is imposed on corn plants (through shading treatments). One estimate from Nebraska suggested a 46% decrease in light intensity for 7 days in mid/late August reduced corn yields by about 5%. At the Northwest Agricultural Research Station (Wood County), daily light integrals over this past weekend (July 17-19) were 0.6-15.6% less than the 10-year average. On the other hand, at the CFAES Wooster Research Farm (Wayne County), the daily light integrals ranged from 9.2% lower to 15.8% greater than the 10-year average.
Haze is a concern as it can reduce light totals, but it can increase the percentage of the light that is diffuse (rather than direct). Diffuse, or scattered, light is more readily used by plants compared to direct sunlight because direct light can overload photosynthetic mechanisms (too much light per unit of leaf area). Haze may also reduce fluctuations in light intensity during the day, which may help plants maintain steady levels of photosynthesis. Fluctuations in light as can happen on partly cloudy days when plants go from full sun conditions to shade (from passing clouds) and back can result in short-term photoinhibition. Acclimation to the different light conditions metabolically can cause a drag/lag in photosynthesis during the ramp-up/ramp-down periods, and can happen multiple times per day. C4 plants (like corn) are much slower to acclimate than C3 species (like soybeans). So, steadier-state light (even if less intense) could help offset lower light/radiation intensities during the hazy period because plants spend less time acclimating to changing light intensity.
The haze that came in late last week is forecasted to move out of the area this week, which also should lessen the impact on this year’s crop. Longer durations of hazy conditions would be more impactful on yields due to the compounding effects of reduced light, but short durations are unlikely to cause significant yield reductions. We will continue to monitor this and will provide additional updates as necessary.
References:
Ortez, O., Lindsey, A., and Wilson, A. 2024. Corn response to long-term weather stressors. OSU Factsheet ANR-0150. https://ohioline.osu.edu/factsheet/anr-0150
Lindsey, A., Wilson, A, Ortez, O., and Lindsey, L. 2024. Effects of haze and weather in 2023 on crop maturation and yield in Ohio. Crop, Forage & Turfgrass Management. https://acsess.onlinelibrary.wiley.com/doi/10.1002/cft2.20299