July 2022 - 14

PLANT & SOIL HEALTH
Call for:
A Washington vineyard in mid-September with phylloxera infestation. Because of
season-long (or longer) root damage from phylloxera feeding, the vineyard lacks a
full canopy, as seen in the far right. Photos: Michelle Moyer/ WSU
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14 | FruitGrowersNews.com
Washington winegrape
growers can prepare for
destructive phylloxera pest
By Doug Ohlemeier
Assistant Editor
Grape phylloxera feed on grapevine
roots and diminish vine health and
vigor. The tiny aphid-like insects
disrupt water and nutrient uptake and
extensively damage
plant root systems, ultimately
killing the plants.
Washington State University (WSU)
Extension researchers developed a risk
assessment map to show winegrape
growers how the pest could potentially
infest their vineyards.
During an April 20 WAVEx web
seminar, personnel from WSU's
Irrigated Agriculture Research and
Extension Center in Prosser discussed
ways growers can deal with the pest.
The map describes areas which may
be of high risk for severe phylloxera
decline, should the insect be introduced.
It doesn't tell growers the risk of getting
the insect. Growers should understand
that if an invasive pest becomes
introduced into an area, it will likely be
a problem, said Michelle Moyer, WSU
Extension viticulturist.
" Risk doesn't mean infestation, " said
Moyer. " You really need to scout. If you
have a vineyard in a moderate to highrisk
area, please sample for phylloxera.
Look for distressed vines and poor
growth. Look for areas of decline and
then go to areas next to them.
" It's a very pocketed, uneven
distribution of this particular insect. It's
hard to scout if you don't have any presymptoms. "
Wart-like
leaf galls shaped like mouse
droppings appear. The mouse droppingshaped,
enlarged root tips are indicative
of phylloxera infestation.
Phylloxera insects develop well in clay
soil with low sand content. Soils with
more than 80% sand are of less risk, with
moderate development possible in soils
containing 65%-80% sand. Soils of less
than 65% sand are defined as high-risk.
Results from a grape phylloxera colony
feeding on winegrape roots. The tiny
aphid-like insects kill the plants by
extensively damaging plant root systems.
Phylloxera moves slowly through
soil.
" Some literature says big, sandy soils
can shift rapidly and crush the insect,
but we aren't sure, " Moyer said. " It
predominantly has to do with that soil
rapidly fluctuating with temperatures
and available moisture. In Eastern
Washington, we have very fine soils
with some large weather extremes
between winter and summer. "
Studies show peak numbers of
phylloxera in late spring and early
summer. While growers get a break in
mid-summer, a second peak can hit
in the fall. In 2019, researchers first
started finding the insect in the fall.
As they began to scout for it, scientists
repeatedly saw infestations early to
mid-May going into mid-June. Once
growers begin practicing regulated
deficit irrigation, they usually have
a harder time finding the pest until
around mid-August. Differences in
locations, soil management and water
can affect the insect, Moyer said.
Phylloxera mimics what looks like
severe stunting or severe drought stress.
By the time a grower sees evidence
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July 2022

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