The Crush - May 2019 - 1

Volume 46 Issue 5 May 2019


Grapevine Virus Management

By Ted Rieger
Some of the grape industry's leading scientists on grapevine
viruses advise growers that the best current practice to prevent
virus spread and vine losses is to remove virus-infected vines
from vineyards as soon as possible after symptoms appear.
That and other practical advice was given at an April mealybug
and virus outreach meeting organized by the Lodi Winegrape
Commission (LWC). Funding for the meeting was from the
American Vineyard Foundation and the California Department
of Food and Agriculture Pierce's Disease/Glassy-winged
Sharpshooter Board.
LWC Grower Communications and Sustainable Winegrowing
Director Dr. Stephanie Bolton said, "It's important to our
industry that we get a handle on this problem. Almost all of us
are seeing more red leaves in our vineyards." Bolton described
California's grapevine virus strategy as: "Decrease vector
populations. Lower virus inoculum." Since the 2018 LWC virus
outreach meeting, Bolton said, "We're definitely making progress
in the area of communications between the key industry sectors
to address this issue."
UC Cooperative Extension entomologist Dr. Kent Daane said
all mealybug species found in California can vector leafroll
viruses, but the invasive vine mealybug (VMB) (Planococcus
ficus) is the most effective vector. The VMB produces more eggs
and has more generations per season than other species - five to
seven generations a year in Lodi, and up to eight generations in
the southern San Joaquin Valley. The crawler stage is the most
efficient vector. Crawlers can acquire the virus within one hour
of feeding on infected vine tissue, and can transmit
the virus within one hour after acquisition.
When a vine is infected by leafroll virus
during the growing season, symptoms will
not be visible until the next growing season.

Red leaves on vines near harvest time are a sign of grapevine virus infection.
Photo: Ted Rieger

The virus is only present in the mouthparts of the VMB. When
the VMB molts to its next life stage, the virus pathogen is lost.
"The VMB is present on the vine with multiple life stages all at
once, including under vine bark, which makes chemical control
more difficult," Daane said. Chemical controls include Movento,
Belay, Admire, Assail, Platinum, Venom, Applaud and Sivanto.
Pheromone traps placed in the vineyard can catch flying male
VMBs, an indicator of VMB presence to aid in timing of control
measures. Pheromone lures are available for mating disruption.
Daane said mating disruption works best in large vineyards and
as part of an area-wide program.
Daane summarized: "The VMB is a very efficient vector, which
makes control more difficult. We can't eradicate the VMB. I think
we have to focus on rogueing infected vines, because it's difficult
to get VMB numbers down."


The Crush - May 2019

Table of Contents for the Digital Edition of The Crush - May 2019

The Crush - May 2019 - 1
The Crush - May 2019 - 2
The Crush - May 2019 - 3
The Crush - May 2019 - 4
The Crush - May 2019 - 5
The Crush - May 2019 - 6
The Crush - May 2019 - 7
The Crush - May 2019 - 8
The Crush - May 2019 - 9
The Crush - May 2019 - 10