May 2022 - 10

Thornton said the 2021 growing
season wasn't just " unusually hot, " it was
" unusually hot early. "
Heat stress during tuber initiation is
particularly impactful on potato plants. If
stress occurs prior to tuber initiation the
plant will often not develop tubers but
instead will continue growing a greater
canopy of leaves.
In 2020, the first 90-degree days
occurred in mid-July. Last year, the first
90-degree day was June 3.
" The timing of the stress in terms of
HEAT, SMOKE IMPACTS
CURB CROP DEVELOPMENT
Wildfire worries ramp up in the Pacific Northwest
Heat stress and wildfires bring unwanted consequences to crops such as potatoes, researchers said.
Photo: Kay Ledbetter/Texas A&M AgriLife
By Bill Schaefer
VGN Correspondent
Where there's smoke, there's usually fire,
and that's certainly been the case in the
Western U.S. in recent years.
The increasing number of Western
wildfires - which cause smoke and
higher levels of ozone pollution - along
with Pacific Northwest (PNW) heat
waves and reports of a megadrought
have farmers facing an ongoing
agricultural crisis of global dimensions.
At the 2022 Idaho Potato Conference,
Mike Thornton and Carrie Wohleb
addressed present and future concerns and
measures to be taken by potato growers
facing these ever-increasing natural
disasters during the growing season.
Wohleb, an associate professor and
potato, vegetable and seed Extension
specialist at Washington State University,
addressed the potential impact of wildfire
smoke, residue and ozone pollution on
potato crop development in the PNW.
cell contents and cell membranes. "
Long-term exposure to high
concentrations of ozone may result in
leaf and plant cell damage. While chronic
exposure to moderate or lower levels
doesn't seem to cause visible injury to
leaves, it may still cause some impairment
of plant function and limit plant growth.
Potato plants, for example, tend to show
a stippling symptom - small black spots -
all over the leaves from ozone exposure.
" New leaves that are produced after the
ozone and other pollutants have dissipated
can be perfectly normal, " Wohleb said.
" This is especially true for indeterminate
potato varieties like Russet Burbank, that
tend to continue to put on new growth
throughout the growing season. "
Whereas plants that have more of a
determinate growth pattern and don't
develop more leaves after flowering, such
as Russet Norkotah, tend to show more
smoke damage.
" In addition to wildfires, ozone can be
formed by lightning strikes, " Wohleb said.
" So, you might see some of those stippling
symptoms after a storm. "
She cautioned to be mindful of
environmental changes created by smoke
combined with weather conditions when
managing your crop.
" During smoky haze, for instance, you
might find that the crop needs less water
and you should irrigate less, " she said.
Smoky conditions sometimes play
Carrie Wohleb, a Washington State
University Extension specialist, discusses
the effects of heat and smoke from
wildfires on potatoes during the 2022
Idaho Potato Conference in Pocatello,
Idaho. Photo: Bill Schaefer Photography
" Wildfires are a problem because they
release a large amount of carbon dioxide,
brown carbon and black carbon particles
and ozone precursors, like hydrocarbons
that when they mix with the air form
ozone, " Wohleb said.
Ozone is one of the more damaging or
harmful pollutants for plants, she added.
" It enters the stomata or the pores on
the leaves surfaces during normal gas
exchange processes of the plant or taking
in CO2 and then once inside it forms
reactive oxygen species that can damage
10 | VegetableGrowersNews.com
positive roles in plant development,
Wolheb said.
" The CO2
from smoke is not really a
negative factor, and it might even be a
positive factor as long as low light from
smoke is not limiting photosynthesis
first - that's that law of limiting factors, " she
said. " Temperatures are often moderated
when there's smoke. So, for many crops
the smoke cover may actually be a positive
factor if it helps to cool things down when
it would otherwise be really hot out. "
The proximity to wildfires makes a big
difference in the impact on the crop.
" The closer you are to those fires, usually
the bigger difference it makes, " she said.
Heat stress
Mike Thornton, professor of plant
sciences with the University of Idaho,
followed Wohleb with a presentation
on the continuing impact of heat stress
on potato crops during the past decade,
with special emphasis on the impact to
the 2021 potato crop.
" Here's the main message, " Thornton
said, " it would be great if we could just
say, 'Hey, yeah, heat's bad for potato
growth and therefore yields are down,' but
it's way more complicated than that. "
The problem is not limited to heat
stress, it's about water uptake, irrigation
management and how to supply plants
with necessary nutrients.
Potatoes are a cool-season crop that
best thrive when temperatures are in the
mid-70s during the day and mid-50s at
night, similar to conditions in the Andes
Mountains, where the crop originated.
Potatoes adapt somewhat to warmer
temperatures, but it's continuous high
temperatures that damage the plants.
" If we have a day or two of hot
temperatures, (there's) very little impact, "
Thornton said. " If we have five to 10 days
where it's 95, 100 degrees, that really starts
to hurt the crop. "
High heat complicates every other
decision potato growers make.
" I like to think of it as your margin for
error. When it's hot you don't have near

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May 2022

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