When dense wildfire smoke wafts in from fires miles away, it brings with it a heavy blanket of smoke particles. These particles act like tiny mirrors, reflecting the sun away from crops.
"When conditions are very smoky, those smoke particles scatter or reflect light and reduce the intensity of light that reaches the leaf," Jones says. "With the light intensity reduced by a smoky sky, there can be less incoming energy to power photosynthesis and the process slows."
Since photosynthesis powers all of a plant's processes, from how fast they grow from seed to sprout to when they ripen, plants need access to quality light. When wildfire decreases light availability, many functions of the plant will suffer. That's why heavy wildfire smoke, particularly in areas like the Pacific Northwest, is a concern for some farmers. Struggling plants mean a less productive yield.
Wildfire smoke doesn't mean imminent doom for a crop, though. The success or failure of a crop that's been affected by smoke ultimately comes down to timing. "In most cases, plants harvested for their fruit or seeds only have one chance to ripen," says Jones. "Reduced light conditions from smoky skies will likely slow ripening, and perhaps if ripening is slowed sufficiently and an early frost occurs that frost could damage or kill the plants before the crop is harvestable."
Jones remembers being called out to a pumpkin crop a few years ago. It had been a particularly smoky summer in Oregon. The Halloween market was approaching, and the farmer's pumpkins were still green. Jones suspected that a smoke-heavy summer was the culprit of immature squash. That was not good news for the farmer's yield come harvest.
"Pumpkins, headed to the jack-o'-lantern market, are one of those crops that have a deadline: Halloween. Those pumpkins may well have 'recovered' and turned color if the skies had cleared, but to the farmer, pumpkins only have real value the week before Halloween and are nearly worthless the week after."