April 2021 - 14

CONTROLLED ENVIRONMENT AGRICULTURE
Tests for viral diseases a guide to identify ToBRFV
By Dean Peterson
VGN Correspondent
The message with viral diseases in the
greenhouse has been to control the thrips
since thrips vector the diseases. That
message has changed with tomato brown
rugose fruit virus (ToBRFV).
ToBRFV is seed-borne and then
spreads plant to plant by touch. This
relatively new virus is a particular threat
to tomatoes and peppers.
" It's thought to be introduced by seed
and then spread mechanically through
handling, " said Mary Hausbeck,
vegetable pathologist in Michigan State
University's (MSU) Department of
Plant, Soil, and Microbial Sciences.
She spoke on virus diseases at the
recent Great Lakes Fruit, Vegetable and
Farm Market EXPO, which was held
virtually.
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14 | VegetableGrowersNews.com
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for decades - impatiens necrotic spot
virus (INSV) and tomato spotted wilt
virus (TSWV) - can infect many different
flowering and vegetable plants. These two
viruses have the same general symptoms,
which can appear on tomato leaves and
fruit, and can include yellowing, bullseye
or ring patterns, mottling or stunting.
Infected tomatoes may become stunted,
and the leaves develop a bronze color
and/or fruit that are off-colored, mottled
and don't develop correctly.
The typical ToBRFV symptom includes
a mosaic or uneven color pattern of the
leaves with a mix of green and yellow.
The leaves may be thin and misshapen.
The wrinkled (rugose) fruit with brown
streaks is very obvious. The fruit rugose
symptom is a clear indicator of infection
by the virus.
There are grower test kits for INSV and
TSWV that give fast and accurate results.
The test kits are easy to use and can
eliminate these two viruses as a potential
source of the problem.
However, there aren't grower test kits
for ToBRFV, and suspect plants must be
sent to a diagnostic lab.
Tomato and pepper seed must be tested
for ToBRFV if it is produced in a country
where this virus has been found, and must
be done before the seed can enter the U.S.
Seed companies have established testing
protocols, but a few contaminated seeds
could possibly slip through.
" Seed testing is only as good as our
current technology, " Hausbeck said.
INSV and TSWV are vectored to
vegetable seedlings by thrips in the
greenhouse that move the viruses from
infected to healthy plants. These viruses
are not spread via seed or greenhouse
workers.
" When peppers and tomato field plants
are diagnosed with INSV or TSWV,
the problem is often traced back to the
greenhouse where the transplants became
infected, " Hausbeck said.
Growing flowers alongside vegetable
transplants increases the risk of INSV and
TSWV. Thrips can hitch a ride into your
greenhouse on ornamentals, carrying the
virus with them.
" When flowering plants are brought
in from several sources, they may harbor
thrips in the flowers or in tight leaf
clusters, " Hausbeck said.
Some infected plants may appear
healthy and serve as a virus reservoir,
but not all plants will show symptoms.
Non-symptomatic plants may be
responsible for keeping the source of
the virus in the greenhouse, which
can then be spread to other plants via
thrips. Weeds in the greenhouse - under
the benches, for example - can also be
sources of these viruses.
" For northern greenhouse growers,
if you don't grow ornamentals in the
greenhouse, you can nearly eliminate
TSWV and INSV on vegetable
transplants, " Hausbeck said. " Quick tests
for INSV/TSWV are easy to use. Keep
them on hand if you're growing both
flower and vegetable transplants in the
same greenhouse. You can test and get rid
of the symptomatic plants, and then test
the neighboring plants to identify those
that are infected, but not yet showing
disease symptoms. " Consider using sticky
traps to monitor the number of thrips and
use an effective control program to keep
their numbers low.
" Getting the thrip numbers down is
really important, " Hausbeck said. " It's the
thrips that are moving the INSV/TSWV
viruses. It's not recommended to grow
ornamentals and vegetable transplants
in the same greenhouse, but it happens.
Scout flowering plants such as dahlias,
begonia, impatiens and other flowers that
are susceptible to INSV/TSWV, and look
for thrips and disease symptoms. "
ToBRFV is highly contagious, infects
tomatoes, and can survive on surfaces
for a few days. In the greenhouse, that
means sanitize and disinfect all surfaces
frequently, and handle the plants as little
as possible.
" If you're short on scouting time,
concentrate on those plants in high
traffic areas where people or equipment
regularly brush against the plants, "
Hausbeck said. Peppers can also become
infected with this new virus.
ToBRFV has been confirmed in several
countries. Isolated outbreaks in the U.S.
have been found in greenhouses that
produce tomato fruit.
The tomato production greenhouses
are especially at risk because the plants
and fruit are handled so much during
pruning, training and harvesting.
Field producers should inspect their
tomato seedlings for disease and send any
suspect plants to a diagnostic lab. " Spray
programs do not help with viruses, "
Hausbeck said. " Infected plants must be
destroyed. I really encourage growers not
to guess on this one. " VGN

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April 2021

Table of Contents for the Digital Edition of April 2021