January 2020 - 17

disease symptoms can appear on both
the vines and the fruit.
Squash are a target
Squashes vary in their susceptibility
to phytophthora.
Spaghetti squash, for example, is less
susceptible. " Use raised beds, plastic
mulch, limit irrigation and choose
effective fungicides, and you can get
along pretty well, " Hausbeck said.
Acorn squash, on the other hand, is
more susceptible.
" It's hard to manage phytophthora
in squash because in some cropping
systems, the fruit lays on the ground
in direct contact with the pathogen, "
Hausbeck said.
The first three weeks of fruit
formation are when squash is most
susceptible to phytophthora. The fruit
of some squash types become less
susceptible after three weeks but fruits
with this " age-related resistance " are
not immune. The fruits also lose this
resistance if they become wounded.
Winter squash and pumpkins are
unique in that the roots, crowns,
stems, leaves and fruits are all
susceptible to the disease. However,
blight symptoms usually aren't seen
on the leaves unless the weather is
rainy for an extended time.
When growing in
a contaminated site
in a field, growers
should be ready
to treat early
and often.
Some cultivars of peppers have been
bred to be tolerant of phytophthora.
" It won't get you through the season, "
Hausbeck said. " You'll see some
symptoms later on. Putting down
plastic, using tolerant varieties and
a fungicide treatment or two is an
effective control program for peppers. "
Some phytophthora isolates vary
in their ability to cause disease so
cultivars with tolerance in some areas
may not be tolerant in others.
Fungicide strategy essential
Preventative fungicide applications
are a must. When growing in a
contaminated site in a field, growers
should be ready to treat early and often.
Fungicide recommendations and fact
sheets on different crops are available
from MSU at www.veggies.msu.edu.
Choosing the right application
method is critical. " It's a soil pathogen, "
Hausbeck said. " You must use a drip
or a drench application where you
get it down into the soil in order to
keep the plants alive. Foliar sprays
are needed to protect against fruit
rot. " This means the products must be
labeled for the particular application
that is desired.
Rotate the fungicides used between
products with different FRAC
VGN | JANUARY 2020 | 15
numbers (Fungicide Resistance Action
Committee) to prevent resistance.
FRAC numbers identify products
with different modes of action and the
numbers are on the product labels.
Resistance is an increasing problem.
" On many farms, phytophthora
has become resistant to Ridomil, "
Hausbeck said.
The best way to prevent
phytophthora is to avoid planting
susceptible crops in fields with a
history of the disease. Power wash
equipment after it's been used in
infested fields to prevent spreading
the disease.
Managing water in the field is key to
managing phytophthora.
Planting into raised beds that are at
least six inches high wherever possible
and using black plastic mulch increase
drainage away from the roots and
crown. The black plastic also keeps
fruit from direct contact with the soil.
Putting plastic down can also prevent
contaminated soil from splashing up
on the crop.
Tiling and improved drainage will
help. Only plant into well-drained
areas and avoid low areas of the field.
Drip irrigation is always preferred.
Minimize the use of overhead
irrigation - especially during fruiting.
Don't irrigate with surface water.
Crop rotation with non-susceptible
crops is always recommended and
never dump diseased culls in the fields.
Scout regularly for phytophthora.
Remove any diseased plants as soon as
symptoms appear. " Destroy a border
of healthy plants surrounding the
diseased ones, " Hausbeck said, since
the healthy-looking plants are probably
already infected.
Harvest as early as possible and don't
let harvested fruit contact infested soil.
Moving production sites may not be a
long-term solution. " Growers have bought
new parcels without phytophthora, but
over time phytophthora became a
problem, " Hausbeck said. This may be
from movement of contaminated soil
via equipment.
Even the best management may still
not get you through the season. " Even
good practices can be overwhelmed by
heavy rains, " Hausbeck said. VGN
http://www.veggies.msu.edu
January 2020

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