Page 57 - Grapevine JanFeb 2022

Around The Vineyard

this, and we already know how to control them.
The difference may be that SWD are attracted not
only to overripe berries but to ripening berries as
well, stretching out our timeline for management.

The Big Fuss About
Spotted Wing Drosophila

SWD is not native to the United States or Canada,
but it is now prevalent throughout fruit-growing
regions of North America. It was accidentally intro-
duced from east Asia in 2008, likely via cargo as
with many invasive pests. It quickly spread through-
out the continent, costing the US strawberry, blue-
berry, cherry, and raspberry industries millions of
dollars; in Minnesota raspberries alone, the pest
causes over $2M per year. The costs come in the
form of damaged fruit, lost marketable yield, and
frequent, expensive insecticide applications.

The feature that makes SWD special from other
fruit flies is that the females have a serrated “ovi-
positor” that they use to pierce the soft skin of
ripe berries to lay eggs inside the fruit. Those eggs
become larvae (maggots) that feed on the fruit,
making it mushy and unsalable. Both male and
female SWD can also introduce bacteria to the
berries that cause fruit rots. They begin to become
attracted to fruit when it is ripe or nearly-ripe fruit
and do not infest green, unripe berries.

Learning what problems SWD poses for the grape
industry will help growers decide if spraying for
SWD is a worthwhile expense.

Injury from birds, wasps, and
splitting makes grapes attrac-
tive to fruit flies, which then
introduce sour rot-causing
bacteria to the berries. Photo:
Dominique Ebbenga, UMN.

Researchers Explore the Impact of
SWD on Wine Grapes

Entomology researchers at University of
Minnesota recently found that the skin of many
cold climate and vinifera grape varieties may actu-
ally be too thick for SWD to penetrate. This begs

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