Page 48 - Grapevine May-June 2020

Around The Vineyard
Currently, these devices are used commercially as
a decision aid for timing fungicide applica-tions.
“These spore traps can help determine when to
initiate sprays at the beginning of the sea-son by
detecting when powdery mildew is present,” said
Lowder.
In their testing, both glove swabs and spore traps
detected the presence of mildew and the re-sistant
mutation to QoI products at similar rates. This simi- should only be employed as a last-ditch effort to
larity showed that the glove swabs could be used in save an already damaged vineyard. For those look-
a similar fashion to spore traps.
Anti-resistance Strategies
Pscheidt offered some recommendations
designed to prevent powdery mildew from spread-
ing. First, watch for bloom, he said, adding that
signs of powdery mildew have been spotted earlier
in the season then they would appear in years past. managers start with a high volume application of
Then, he said, adjust the programs in order to be in water (200 to 400 gallons/acre) plus a wet-ting
a position to begin applications when the vineyard
hits 10% to 50% bloom.
Rotate the individual fungicides chosen or use
a mix by combining two fungicides into the tank.
Start a fungicide program with multi-site, mode-
of-action materials, taking care to limit the total
number of applications in any one group, as well
as using labeled rates of sulfur. Prepackaged mixes
can be useful in this regard, though one needs to
make sure not to mix biological and anti-microbial
products.
In terms of how to best spray these fungicides,
the OSU team experimented with reducing the
number of gallons per acre using a laser-guid-
ed intelligent system sprayer. The smart sprayer
reduced the amount of pesticide used per acre and
got the same level of control as a regular sprayer,
as long as the amount of sulfur used did not go
below labeled rates.
Dealing with a Vineyard
Powdery Mildew Outbreak
Prevention in the vineyard is key to avoid prob-
lems with powdery mildew. According to OSU’s
Extension Service’s website, “The best powdery
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mildew management plan is to attend to details
before and during the spray season, especially
during the transition into and during bloom.”
According to Pscheidt, if one needs to do rescue
in order to save the crop, it’s probably too late.
“Once grapes are damaged, they’re damaged,” he
said. “A vintner can make wine from these grapes,
but it won’t taste very good.” Hence, a rescue
ing to rescue their vineyard, Pscheidt stresses that
oils are the only things that can eradicate powdery
mildew when it hits the rescue stage.
Also, on OSU’s Extension Service’s website,
Pscheidt outlines a three-step “spa” treatment to
rescue a vineyard infected with powdery mildew.
The first step is a water bath. He recommends that
agent (surfactant) to wash off all the spores from
the grapevine, which will prevent them from being
dispersed to healthy parts of the grapevine. Be sure
to cover the entire vine, with a particular focus on
the clusters. However, as new powdery mildew will
develop rapidly within a day or two, this should be
seen as a very temporary measure and not a long-
term solution to eliminate powdery mildew.
Next, apply horticulture mineral oils to these
vines. As most of the mycelia reside on the outside
of the plants, these oils will denature the fungus.
They recommend a 1-2% oil treatment to the vines
within two days after bathing the vines. Spray thor-
oughly for best results. They recom-mend petro-
leum-based oils over plant-based oils, as well as
avoiding bicarbonate products. Be-fore using sulfur,
be sure to follow the labeled intervals in order to
avoid leaf burn.
The final step is a complete cover of the entire
vineyard. After applying the oil, wait five to sev-
en days. Then apply a strong fungicide. Be sure to
pay attention to the spray application and product
selection. Go slow to ensure that the entire vine
gets thoroughly covered.
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4/28/20 1:21 PM