January 2019 - 15

* Planting seed for re-certification
with 0 percent or nearly 0 percent
PVY for early generation seed.
* Roguing out PVY-positive plants
early in the growing season.
* Killing potato vines early to
minimize risk from late-season
winged aphids moving PVY.
* Border cropping (such as nonhost
grasses or PVY-resistant.
potato varieties such as Payette).
* Other cultural controls, including
mulches and intercropping.
* Promotion of beneficials by
limiting use of pyrethroids.
* Insecticides.
* Mineral oils.
Using mineral oils and
insecticides
No insecticide can completely protect
a plant from infection by a
PVY-virus-carrying aphid that lands on
and probes a potato plant. Such infection
is driven primarily by viruliferous noncolonizing
aphid species that move into
a potato field searching for a suitable
host. However, insecticides that protect
potatoes against potato-colonizing
aphids (like the green peach) can help
reduce further spread of PVY within a
field. Thus, although insecticides can be
important tools for reducing in-season
spread of PVY, they are not sufficient on
their own.
In Idaho, some growers are adopting
the use of mineral oil in conjunction
with insecticides as part of an effort to
limit in-season movement of PVY in
seed potatoes. However, the approach
hasn't been fully tested as an effective
tool in Idaho. Preliminary work
conducted at the University of Idaho
Aberdeen Research and Extension
Center (Bingham County, Idaho) has
demonstrated that the approach does
not work when applied on a seven-day
schedule in a commercial potato growing
area with high PVY pressure (see
graphic). Questions remain about when
to begin applications, how often they
should be made, the mode of application
(aerial vs. ground rig), and whether
overhead irrigation will impede efficacy.
More work is required to address these
and other questions in seed-growing
areas of Idaho that feature relatively low
PVY pressure.
In a high PVY-pressure growing area
in Idaho, a mineral oil and insecticide
regimen did not suppress in-season
movement of PVY (PVY incidence
is based on a random postharvest
100-tuber sample submitted to a winter
grow out trial, with a leaf from every
plant tested via ELISA).
When considering a mineral oil plus
insecticide regimen to help reduce the
amount of in-season spread of PVY in
seed potatoes, it's important to read,
understand, and follow the
label instructions, as well as to
implement an insecticide resistance
management plan. Any light mineral
oil is reportedly effective, and use
of insecticides, such as Movento
(spirotetramat), Fulfill (pymetrozine)
and Beleaf (flonicamid) that are friendly
to beneficials is encouraged.
Ultimately, there is no silver bullet for
the seed potato grower to prevent the
movement of PVY from infected to healthy
plants. Thus, a program that relies solely
on mineral oils or in conjunction with
insecticides is likely to result in variable
results. Instead, a multi-faceted approach
is optimal (though still no guarantee!) to
limit the opportunities for PVY to increase
in seed potato production.
(This story is one of a series of
research reports from the Potato
Association of America that can be
found in our sister publication, Spudman
magazine. For more information, visit
www.spudman.com.) VGN
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Many species of aphids are the vectors
for potato virus Y.
Use of mineral oils has been
recommended as a means to reduce inseason
PVY movement since the 1960s.
The mode of action of mineral oils is not
yet fully understood. Initially, researchers
speculated that the oil interfered with
aphid feeding or probing behavior.
Later hypotheses include interference
in the ability of aphids to take up or
transmit virus particles and restriction of
movement of virus particles within the
plant. Although the mechanism remains
unclear, mineral oil in combination
with insecticides has been shown to be
effective in reducing PVY.
Recent work from New Brunswick,
Canada, showed that the best reduction
in PVY in-season movement was
achieved with applications of mineral oil
every five days with five of the total 14
applications being tank-mixed with an
insecticide. The oil was mixed in water to
a final solution of 2 percent vol:vol, with
an application rate of 200 liters of water
per ha at 80 PSI using a tractor-mounted
ground sprayer.
Tom Pagels
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January 2019

Table of Contents for the Digital Edition of January 2019
