Cannabis Guide - 2020 - 16

PLANT HEALTH
PREVENTION AND CONTROL
1. Keep grow rooms clean of soil and plant debris as these
can harbor Pythium and Fusarium mycelium and spores.
Most cannabis
root and stem rots
occur between
transplanting of
the newly rooted
clones and the
first three weeks
of vegetation.
" damping off " (Figure 1). Above ground the cannabis plants
often show yellowing of the leaves, stunting and general leaf
wilt even if root zone has been properly irrigated.
In general, most cannabis root and stem rots occur
between transplanting of the newly rooted clones and the first
three weeks of vegetation as the young plant tissue is most
susceptible. Once the cannabis plant establishes a more mature
root system and thicker stems it is less likely to succumb to
damping-off by Fusarium and Pythium and often the plant can
grow out of an existing infection. The single biggest factor to
influence whether your young cannabis plants get infected by
these root rot organisms is a water-logged root system. Overly
continuous wet soils starve the root zones of oxygen and
weaken the health of the young cannabis plant, thus increasing
the susceptibility to fungal infection.
Pythium is referred to as a fungal-like organism or
water mold. Unlike true fungi, Pythium differ in mycelium
structure and that they produce oospores inside the roots
and zoospores that can swim in water. These water molds
thrive in persistent wet soils, hydroponic media, plant
debris and recirculating systems.
Fusarium is a large group of pathogenic and saprophytic
fungi that are economically important due to their
devastating impact on crops. The Fusarium fungi can be
found in the soil, plant debris and plant stems including
mother plants, which can act as a long-term host and source
of mycelium and spore inoculum. The fungus produces
abundant spores that can spread to other plants via
contaminated tools, soil, water and air.
16 2020 GUIDE TO CANNABIS PRODUCTION
2. Disinfect grow room surfaces periodically as well as
pots and tools before reusing them. Bleach, H2
products that contain peroxyacetic acid (PAA) like
Jet-Ag* work well. The PAA and H2
O2 and
02 materials can also
be used as a periodic root drench to disinfect the grow
medium as well as a disinfecting spray for the leaves
and stem.
3. Clean air of fungal spores through high-quality air
filtration units. This will also help with other important
cannabis fungal diseases including powdery mildew
and Botrytis bud rot. UV-C disinfection units and
high-quality air filters are becoming standard in
cannabis production.
4. Maintain proper soil moisture in the root zone and -
more importantly - avoid water logged conditions
that lead to low oxygen levels. The addition of perlite to
your peat moss or coco coir media will increase the air
spaces and drainage of your root zones. Rock wool is an
ideal growing media since it is sterile and contains high
amounts of airspaces even when fully irrigated.
5. Proper fertilization and pH will enhance plant health
and its ability to fend off diseases naturally. Young
cannabis plants that are under fertilized are weak and
are more susceptible to pathogenic and environmental
stressors. Conversely, over fertilization can lead to high
salt concentrations in the soil and thus can be toxic to
roots and the leaves exhibit nutrient imbalances and
burn. The addition of soluble silicon like potassium
silicate (K2
diseases and insects as well as environmental stressors
like heat, cold and drought.
6. Inoculation of the root zone with beneficial organisms
like mycorrhizae, Bacillus, Trichoderma and
Streptomyces species can help prevent Fusarium and
Pythium infections and increase root and plant health
to better defend against disease. Regalia CG* is a
popular biofungicide that increases the cannabis plant's
own defense mechanisms and increases root and plant
health to prevent root and stem rots, powdery mildew,
and Botrytis bud rot.
Follow these easy to implement preventative and curative
measures and you will be on your way to healthy, diseasefree
cannabis plants that will grow up and produce highquality
flower. v
Matthew Brecht is cannabis key account manager with
Marrone Bio Innovations and can be reached at mbrecht@
marronebio.com. Visit www.marronebio.com for more
information on how to control cannabis pests and establish
production protocols.
*Jet-Ag and Regalia are registered trademarks of Marrone Bio Innovations Inc.
SiO3) can enhance that plants ability to resist
http://www.marronebio.com
Cannabis Guide - 2020

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