The Crush May 2022 - 1

theCrush
Volume 49 | Issue 5 | May 2022
FEATURE STORY
Virus and Mealybug Management
COOPERATION, AREAWIDE PROGRAMS REDUCE SPREAD
Article by Ted Rieger
Grapevine leafroll viruses and grapevine red blotch virus
contribute to significant economic losses for California winegrape
growers by reducing grape and wine quality and grape yields, and
by their impacts on vine health and vineyard lifespans that result
in more frequent vine removals and replants. The Lodi Winegrape
Commission (LWC) held its third " Mealybug & Virus Outreach
Meeting " in April with a focus on programs and management
strategies to prevent and reduce the spread of leafroll virus and
reduce mealybug vector populations. Rogueing infected vines
annually after harvest is a key strategy to reduce virus inoculum
and spread. Greater success can often be achieved when growers
work together through areawide programs, and cooperate
to monitor vine mealybug populations and employ mating
disruption measures to reduce vectors.
VMB VECTOR MANAGEMENT
UC Berkeley and UC Cooperative Extension entomologist Kent
Daane said the vine mealybug (VMB) (Planococcus ficus) is in
most major California grape growing regions and advises growers
to engage in areawide programs while also acknowledging, " We'll
never completely get rid of it. " Given the VMBs reproductive
cycle, it's common to see all generations on the vine at one time.
Available pesticide materials only work on certain VMB life stages.
Daane said, " We can keep it out of grape clusters with the tools we
have, (to prevent cluster damage/grape losses) but we can't get to
it under the bark where it's hard to kill. Ants can also be a problem
in protecting mealybugs from predators. "
Crawlers are the most likely VMB stage to move leafroll virus from
vine to vine. Although this stage is mobile and can crawl short
distances, crawlers can also be transported by wind, workers,
equipment, and birds. Daane said, " This is why we need
areawide programs. It's not just a risk coming from your
neighbor's block, it can travel longer distances by wind
and equipment. " Once a VMB is on a vine
infected with leafroll virus, it can acquire the
virus within 1 hour, and once acquired, it can
transmit the virus in 1 hour.
UC researcher Nathan Mercer, who works with Daane on control
trials, discussed recent mating disruption trials using VMB
pheromone products such as the Isomate VMB twist tie dispensers
placed on vines or the trellis at different densities ranging from
25 to 150 dispensers per acre. Other mating disruption products
include hang tags, flowable and puffer dispensers and sprays.
Although it can be more expensive and time consuming to place
more dispensers, Mercer said, " The more mating disruption
Hedgerows between vineyard blocks can prevent mealybug
movement and reduce leafroll virus spread. (Photo: Ted Rieger)
measures you use and the more dispensers you use, the more
you can reduce VMB populations. It also works better the more
years in a row it's used, with better results year after year. " He also
explained, " The lower the pest population, the better mating
disruption works, but it can be effective even at higher population
levels, especially when used in combination with pesticide sprays. "
Chris Storm, PCA with Starr and Storm Crop Solutions in Lodi and
former viticulturist at Vino Farms, suggested planting hedgerows
to reduce VMB and virus spread between vineyard blocks,
particularly when replanting a vineyard in a location where
infected vines are nearby. He cited a trial study at a Vino Farms
vineyard in Lodi's Borden Ranch AVA that showed only one virus
The Crush May 2022

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