Page 47 - Grapevine May-June 2020

Around The Vineyard

Monitoring Fungicide Resistance

Sarah Lowder, a third-year doctoral candidate
at OSU, offered a succinct analysis of the types of
resistance exhibited by products available to con-
trol fungus in the vineyard. “The type of re-sistance
exhibited by DMIs (FRAC group 3 such as Rally or
Procure) often has several muta-tions where the
fungus becomes more tolerant of the fungicide.
The other type of resistance can be sudden due
to a single mutation. Products like the QoIs (FRAC
11, such as Abound or Flint) that exhibit this resis-
tance are often classified as ‘high resistance risk,’
but they also are easier to monitor using modern
approaches.”

Collecting samples represents a key challenge in
testing for powdery mildew in the vineyard. “When
doing visual scouting, not only does it take more
time than most growers have during the season,
we also get a lot of false detects as scouts misiden-
tify the disease,” Lowder said.

To address these concerns, they tested swabbing
a worker’s gloves in order to ascertain if this could
be a viable way of collecting spores quickly and
inexpensively.

They tested this theory by taking swabs from
worker’s gloves using cotton swabs with a plastic
cap. Then, they compared those swabs with data
obtained by swabbing the leaves directly. In both
tests, they obtained samples from the same cano-
pies to ensure consistency in testing.

Their analysis of the results proved testing a swab
from a worker’s glove produced a 96% accu-racy in
detecting resistant powdery mildew. Additionally,
they found that glove swabs could de-tect the
presence of powdery mildew in a vineyard better
than the visual scouts. Thus, these sam-ples were
faster and more efficient than visual scouting. As
a side note, they tested different glove materials
and discovered that the type of glove worn by the
workers made no difference regarding the degree
of accuracy.

They also tested the efficacy of glove swabs in
comparison to Airborne Impaction Spore Traps.

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