June 2022 - 11

Tips presented to curb
asparagus disease damage
By Dean Peterson
VGN Correspondent
Foliar disease damage from purple
spot and soilborne disease damage
from crown and root rots are still
major threats to asparagus. That's
the message from Mary Hausbeck,
Michigan State University (MSU)
vegetable disease pathologist.
Hausbeck talked about the diseases
at the 2021 Great Lakes Fruit,
Vegetable & Farm Market EXPO in
Grand Rapids, Michigan.
Purple spot (Stemphylium
vesicarium) can damage both the
ferns in the fall and the spears the
next spring.
Diseased ferns brown prematurely
and defoliate, reducing the
photosynthesis and yield the following
spring. Heavy disease pressure in the
fall results in more overwintering
inoculum in Michigan's no-till system
which means more emerging spears
may become infected and develop the
purple spots.
" In the 1990s, we were primarily a
processing industry, so spotting of the
spears was not considered a big deal,
but now that we have an important
fresh market industry, the spots are a
deal breaker, " Hausbeck said.
There is no chemical control
available for purple spot during the
spear stage. The only way to manage
it is to reduce the amount of disease
present in the ferns the year before.
" It's important to keep the fern
healthy during the summer and into
the fall to have the best yield the next
spring, " Hausbeck said. " It only takes
one lesion to cause a needle to fall off
and contribute to early defoliation. "
Bravo WeatherStik (chlorothalonil)
and Roper (mancozeb) have been the
core program used for disease control
on the ferns. The sprays are timed
using the TOMCAST computer model
with the last treatment generally
applied around Labor Day.
" Are fungicides needed in the fall? "
Hausbeck asked. " The answer depends
on the weather. We've had some warm
falls. The purple spot pathogen will
continue to progress if the weather
allows; it doesn't
stop on Labor
Day. There is
the potential
for a significant
fall outbreak
allowing a large
amount of the
pathogen to
overwinter. "
MSU
MARY
researchers have
evaluated some new products for fern
disease control. The treatments were
made from July 8 through Sept. 8 and
alternated with Bravo WeatherStik.
Disease severity ratings were taken on
HAUSBECK
Sept. 9.
" Miravis Prime was highly effective
against purple spot, " Hausbeck said.
" Statistically, it stood out from the
other products. Merivon was also
very promising. "
Although the spray treatments
had stopped, evaluations of the
amount of foliar purple spot disease
continued into the fall, on Sept. 30,
Oct. 13 and Oct. 20. By late October,
the effectiveness of many of the
tested products had faded and the
ferns were showing disease severity
and defoliation ratings close to
three-fourths of the severity of the
untreated plot.
The Oct. 20 evaluation showed both
Miravis Prime and Merivon remained
significantly more effective than the
other products, although Merivon had
disease severity ratings close to double
that of Miravis Prime.
" We really need to have the Miravis
Prime and Merivon as part of our
control program because they're so
effective, " Hausbeck said. The study
also showed that Luna Experience and
Luna Tranquility hold promise.
The next step is for the industry
to proactively work with the
manufacturers gathering efficacy and
crop safety data for new registrations
and submitting a project clearance
request through the IR-4 program.
Fusarium crown and root rot
(Fusarium spp.) and phytophthora
spear, crown and root rot
(Phytophthora asparagi) are the main
soilborne pathogens of asparagus.
Healthy crown and root tissue
should be all white; the color of
diseased tissue differs between the two
diseases. Fusarium crown and root
rot symptoms include a red-brown
discoloration of lower stems and
crowns, and red-brown lesions on the
roots and lower stems. Phytophthora
spear, crown and root rot symptoms
include discolored storage and feeder
roots that may appear to be gray and
water-soaked.
" Phytophthora is a relatively new
pathogen to this industry that is
especially destructive, " Hausbeck
said. " We have tested fungicides
and biocontrol products for their
effectiveness. "
Cannonball, Presidio, Ridomil
Gold, Topsin and Serenade, a
biological, have been evaluated in
the asparagus crown nursery. With
applications made every 21 days
(July 1, July 21 and Aug. 11), and
using crown health ratings, there
were no observed differences in the
products' effectiveness, and all of the
fungicides had good crop safety.
Crop safety is a major concern of
the companies when considering a
product registration for a new crop
such as asparagus.
" Companies want to know there is
no injury as a result of their product
being used, " Hausbeck said.
Disease control data may already
exist from research on a similar
disease on another crop. The
fungicides Presidio and Topsin are
not registered for use on asparagus
seedlings in a crown nursery, but
are being tested. Presidio targets
phytophthora and Topsin targets
fusarium.
" We want to get more products
registered for use in the seedbed and
for the nursery industry, " Hausbeck
said.
Cannonball is registered for use in
Michigan as a crown soak. Ridomil
Gold can be used after planting
seedlings or after covering one-yearold
crowns.
" They're here; they can be used, "
Hausbeck said.
Research will continue to expand
tools that can be used in the crown
nursery.
" We started with crown soaks, "
Hausbeck said. " We soaked them
after they were dug from the nursery
and before they were planted in the
production fields. It takes time to
soak the roots. When you're trying to
disinfect something, time of contact is
meaningful. Crowns are closely spaced
in the nursery, and so treatment
applied in the nursery has the
potential to positively impact a high
number of crowns that are planted
across a lot of acreage. " VGN
VGN | JUNE 2022 | 11
June 2022

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