March 2022 - 15

GLVPN VEG CONNECTIONS
in Food Research and Action Center
(FRAC) groups 11 and 3 appear to
have a good to very good efficacy
on tar spot, along with similar high
efficacy ratings for leaf blights and
rust, with a pre-harvest interval
(PHI) on most of these products
between seven days and 14 days
when used on sweet corn.
So, it may very well be that the
single-ingredient products that
growers already have in the shed will
work just fine here, such as Quadris,
Headline, Tilt and Toledo. But, how
often should they be applied if the
conditions are heavy?
In field corn, Marty has
documented 50-bushel protection
from one well-timed application
at around green-silk, but a second
application three weeks later has
helped in some situations. Given
the harvest timing of sweet corn,
it is reasonable to expect adequate
control with one application of
an effective fungicide, though the
application timing would need to
account for the PHI.
Don't get stuck in a rut
Snap beans are susceptible to a
complex of pathogens as seedlings,
including the fungi fusarium and
rhizoctonia, and water molds
phytophthora and pythium. Early
plantings are at the most risk, and on
farms where irrigation is available,
it is common to find oneself chasing
your own tail. The beans start to wilt
because of one of these pathogens
nipping at the roots, and then a
shallow irrigation pass is made to
limp them along with the roots they
have left, but then that drives the
pathogen load up.
Crop rotation and irrigation
management are important measures
to try and keep some of these
pathogens at low levels. Marty
shared one example of a dry bean
field with center pivot irrigation.
The grower had not yet run the pivot
for the season, but there were very
clear root rot symptoms under the
pivot compared to outside the pivot.
What this meant to him is that beans
had been under this unit too often,
and too often they were irrigated.
These factors combined to make a
perennially favored environment for
these pathogens to build to a high
population level under the center
pivot.
Are there fungicidal options?
Yes, and the most effective delivery
for them is in the furrow or on the
seeds themselves. Covering your
bases against the true fungi and the
water molds requires at least two
ingredients. In the vegetable world
there are different seed treatments
available than in the field crops world,
and they come in an array of premixes
as well, such as FarMore. Some of the
single-ingredient seed treatments that
are effective on fungi include Captan
4F, Dynasty, Maxim 4FS, Mertect
340-F, Stamina, Systiva XS, and
Thiram 480. Banded/soil treatments
for fungi include Quadris, Blocker
10G, and Headline. For water molds,
seed treatments include Apron XL,
and banded/soil treatments include
Presidio, and Ridomil Gold SL. Be
sure to always read and follow the
label.
Flushing out white mold
White mold is a fungal disease
that forms a long-lived dormancy
structure, called a " sclerotia. " The
sclerotia, which look like mouse or
rat droppings, fall into the soil and
can survive for many years there. But,
when humidity is high and you've
got about 40% canopy coverage,
the sclerotia make mushrooms that
produce wind-blown spores. The
spores infect many broadleaved
vegetable crops primarily through
dying flowers and leaf material,
stems and root crowns. A unique
feature of this pathogen is that it is
" monocyclic " , meaning that it does
not spread readily from plant to plant
within the season. So, the first initial
spore-release is often the primary
infection opportunity.
A common recommendation is to
deep plow to bury the sclerotia. But, if
you do that, then you've incorporated
some of those sclerotia into your
crop plan for the next two to four
years. Marty shared that research from
Cornell University that has shown
no-till planting a winter-hardy grass
like wheat or cereal rye creates a
favorable microenvironment in the
spring that causes the sclerotia on the
soil surface to sporulate early, ahead
of the normal flowering time of many
broadleaf crops. When there is nothing
to infect - because it's a non-host
crop - then the threat depletes itself.
But, if you've got a population in
your field and it wasn't flushed out
with a no-till winter-hardy grass, is it
possible to predict when the pathogen
is sporulating and get a fungicide on
to protect the plants?
The answer is yes, and there is
about a three-week window for
application of effective fungicides
when the conditions are good, and
the crop is at a susceptible stage.
One resource is an app called
Sporecaster, which channels weather
data for a specific location to predict
sporulation in a typical soybean field.
It is not designed for hoop
house tomatoes, for example, but
for other field-planted vegetables
with comparable row spacings and
planting timings, this could be a
useful tool for predicting sporulation
and timing a fungicide application.
Suppressive fungicides labeled for
several vegetables include Aproach,
Cannonball, Endura, Fontelis, Mettle,
Omega, Priaxor, Proline, Quadris,
Rovral, Toledo and Topsin.
To learn more about what the
Chilvers lab is up to, visit
canr.msu.edu/fcp. VGN
VGN | MARCH 2022 | 15
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March 2022

Table of Contents for the Digital Edition of March 2022
