Page 17 - 2025 GM spring

Microdochium
Patch
Figure 3*
continue to be used to refer to the
disease that occurs without snow
cover. It’s all a matter of opinion.
WHAT CONDITIONS FAVOUR
DISEASE?
Fusarium Patch will occur when
temperatures are between 0-15°C
with leaf wetness periods of greater
than 10 hours a day for several days.
Pink snow mold occurs under snow
cover, with disease development
enhanced by slowly melting snow,
and more pronounced disease with
longer snow cover. Both diseases are
often more severe in shady areas
with poor air circulation, poor
drainage and a thick thatch layer.
Heavy applications of fast-release
nitrogen and heavy topdressing
serve to increase disease levels,
probably because it causes the grass
to grow under conditions where it
might be prone to cold injury. Mid to
late fall soluble nitrogen applications
may prevent the grass from properly
preparing for winter.
Normally, grasses going into the
fall will reduce photosynthates in the
leaf blades by stopping production
and exporting sugars to the roots.
Grasses will also ‘harden off’ by
exporting water out of the cells
which decreases the chances of
injury from freezing, especially during
the freeze-thaw cycles of winter
sunny days with night-time below
freezing temperatures.
WHAT IS THE DISEASE CYCLE OF
THIS FUNGUS?
Microdochium nivale survives through
the summer as spores and mycelium
in thatch or soil and is generally not
active when temperatures are above
20 °C or when it is dry (Figure 3). In
autumn, under cool, wet weather,
spores may germinate, or microscopic
* adapted from Tronsmo et al., 2001; illustrated by Kathryn Wilde.
fungal growth called hyphae (pink
tiny strands) may grow from thatch
or soil and infect leaves. Spores are
carried by wind or surface water to
adjacent healthy leaves. The fungus
may attack foliage under snow cover
especially if the plants have not
hardened off and are damaged by the
cold temperatures or have become
weakened (storage materials used
up) by prolonged snow cover. After
snowmelt, the fungus remains active
with the late winter or early spring
weather, particularly if it remains cool
and wet, and Fusarium patch
continues to develop (Figure 2).
RECENT DEVELOPMENTS IN
DISEASE CONTROL
The fungus Microdochium nivale has
shown field resistance to fungicides
in the DMI group (such as Banner and
Eagle), and the dicarboximide group
(such as Rovral). For areas with full
blown resistance (where most
individual fungal isolates in the
population have resistance), regular
rates of the fungicides do not provide
full duration protection and may
provide no control at all. Moderate to
high levels of resistance to these
chemical families have been
documented in British Columbia and
Ontario, and resistance probably
occurs wherever use of these types
of chemicals is frequent. Some non-
conventional fungicides have also
shown activity against this disease.
These include products such as
Civitas Turf Defense & Civitas
Harmonizer, phosphorus acid, sulfur,
and iron sulfate. Look in provincial
publications for permitted uses. GM
GreenMaster • CGSA •
17