June 2019 - 19

GRAPES
breeding cold-climate grape hybrids grape
breeding, the University of Minnesota.
" They've got about 110 acres there
... that's where their winegrape cold
varieties are being grown, " White said.
At the time, Minnesota wasn't aware of
grapevine trunk diseases there, he said.
He determined the presence of
new diseases by sending diseased
trunk samples to labs in California in
addition to ISU's own plant science lab.
" All of the sudden, all these diseases
we never had in Iowa started popping
up, " he said.
It's a relatively new science. In 2000,
White said, only 15 species of fungus
were identified as causing grapevine
trunk diseases, but today there are
230. Trunk diseases cause an estimated
$260 million per year in economic
losses, he said.
In many cases, signs of disease such as
a discolored trunk or leaves don't always
show until the plant is stressed, he said.
" When you read about trunk diseases
in South Africa or California, or
Australia, or anyplace in the world ...
you've got them here. And you may have
them worse because you have something
they don't have: Winter injury. "
What you can do
Diagnose. Cut live-cordon sections,
wrap them in plastic and send them
quickly to a lab. White recommended
two California labs - Trical
Diagnostics in Gilroy or AL&L Crop
Solutions in Vacaville - but more
recently, Michigan State University
Diagnostic Services has also hired staff
with commercial experience testing for
grapevine trunk disease.
Get rid of pruned limbs. Compost
them or burn them, but most
importantly get them out of the
vineyard. " Most of these grapevine
trunk diseases are living on that
residue, " White said, and the fungi
can send out spores when the weather
warms up.
Sanitation. Some people try cleaning
their pruning equipment with Clorox,
water, alcohol and even fungicide. White
didn't recommend this.
Double or long pruning. Bot and
some other fungi will enter the vine
through spores that find pruning scars,
White said. It can work its way toward
the roots at a rate of 3-6 inches per year
and the whole plant will be infected
once it reaches the graft union. A final,
follow-up pruning in the spring will
allow the pruning scars to " bleed " sap,
cleaning out fungi, and the scars will
heal more quickly in the warm weather,
White said. " What that does for you, is
those new pruning scars, at that new
temperature, will heal over much faster. "
Always have renewal suckers ready
to replace old, diseased cordons. A
healthy vineyard should yield about
4 tons an acre. " Be renewing that
constantly to keep your yields up, and
cut out that infected stuff before it gets
on the trunk, " he said.
Don't prune in the rain. Rain
increases the production of diseasecausing
airborne fungal spores.
Barrier products. Several different
products are available for painting
pruning scars or vine trunks, although
plain latex paint is also used by some
growers. Many include boric acid in
a paste or paint. White said fungicide
in the paint is also proving effective.
" Right now in California, everybody's
painting their pruning scars, or they're
spraying them on, " White said. " What
you want to do is apply this within 24
hours after pruning. "
Fungicides. White said he was aware
of three fungicides labeled for protection
against major grapevine trunk diseases
in the U.S.: Topsin-M, Rally and Mettle.
Some growers are mixing fungicides
in barrier products. A spray dye is
recommended to ensure the pruning
wounds are covered. Natural fungicides
for grapevine trunk disease include
Trichoderma and Bacillus subtillis -
both of them, he said, are marketed
under numerous labels. They are " fungal
organisms that cover and colonize the
wound preventing further infection, "
according to his presentation. FGN
Wild grapes in the Midwest are often
hosts for disease, as shown by this wild
grapevine in Indianola, Iowa.
Grapevine samples prior to being
mailed off to a lab for diagnosis. It's
recommended to wrap the vines in plastic
prior to express shipping.
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FGN | JUNE 2019 | 19
http://www.oescoinc.com
June 2019

Table of Contents for the Digital Edition of June 2019
