September 2021 - 34

PLANT HEALTH
practices that are recommended will go a long way in avoiding disease
infection.
" I expect growers will also have to apply more preventive fungicide
applications. It may even get to scheduled calendar-based applications.
Some growers are already doing this. It is becoming more difficult to
apply fungicides for specific diseases on different plants. "
Scouting the plants will become even more critical to identify disease
infections.
" The sooner growers can identify early disease symptoms, the better
the chance of controlling the disease, " Williams-Woodward says.
" Diseases don't disappear, so growers should keep good records of
disease incidents, when they occurred and how they were treated. These
records can be useful in knowing how to treat a disease if and when the
disease reoccurs. "
IMPACT ON PEST DISSEMINATION
The FAO report indicates that invasive pests cost countries as much as
$70 billion annually. Josh Vlach, entomologist at the Oregon Department
of Agriculture, and his colleagues are working to keep invasive species
out of the state.
" Dealing with pests outdoors is more difficult than controlling pests
indoors because there are many more variables including typically
Verticillium wilt is
caused by a soil-borne
fungus that usually
enters through a plant's
roots. The fungus
produces toxins that
clog a plant's vascular
system preventing leaves
from receiving enough
water so they yellow
and wilt. Photo: Jean
Williams-Woodward
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EVERYTHING WATER
trying to provide control over a larger area, " Vlach says. " This makes
incorporating biological control agents outdoors more difficult and
more expensive.
" In Oregon we have been accumulating on average nine non-native
pest species per year. These are all new pests with one in five considered
to be a significant economic pest. Every year, on average, a significant
economic pest is being brought into the state. "
Vlach is particularly concerned about the effect warming temperatures
will have on pests entering Oregon.
" As the climate changes, it is getting drier and warmer in Oregon, we
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34 SEPTEMBER 2021 GPNMAG.COM
are starting to see some warm-climate pest species having the ability to
become established here, " he says. " There are people in Oregon who are
growing warm climate plants, including almonds, eucalyptus and bananas,
with some of them having the ability to become established here.
" One of the things growers can do is to start to trial and select plants
that can adapt to the changing weather conditions. The U.S. Forest Service
(www.fs.usda.gov/ccrc/tool/seedlot-selection-tool) is already doing this.
Trees are being brought in that can tolerate drier, hotter conditions. "
Vlach says selection pressure drives evolution. Climate extremes are
causing selection of pests that will do better under these extreme conditions.
" These pests have to deal with higher temperatures, drought conditions
and higher rates of precipitation, " he says. " Developing resistance to
pesticides is another selection pressure. The more organisms that are
produced the more chances there are for variation and selecting for
different traits.
" Increases in generation times causes more generations per season
which is the situation where insects can best develop resistance. If there
is exponential growth with multiple generations in a season there is an
increased chance the pests are going to develop resistance to pesticides. "
As temperatures warm, pests that wouldn't have been able to survive
Oregon winters outdoors are now becoming a year-round pest for both
indoor and outdoor growers.
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September 2021

Table of Contents for the Digital Edition of September 2021
