Cannabis Guide - 2022 - 14

DISEASE MANAGEMENT
Cannabis plants with powdery
mildew will have a slightly dull
appearance as mycelium develop
across the leaf surface.
Photo: Griffin
The Big Three
How to prevent and manage the top diseases affecting cannabis plants.
By Ana Olvera
S
everal factors can affect the production of a healthy
cannabis crop - diseases being among the most
common and difficult to control once established.
GPN recently caught up with Tami Van Gaal and Erica
Hernandez, CEA specialists at Griffin Greenhouse Supplies,
to learn how growers can identify, control and prevent the
three most common diseases found in indoor cannabis
production: powdery mildew, Botrytis and hop latent viroid.
Powdery mildew and Botrytis are two foliar diseases
capable of decimating a crop if left unchecked. Both of these
spores are fairly ubiquitous in the environment, making it
hard to completely eliminate exposure. Of the two, powdery
mildew tends to be harder for growers to control and the
biggest reason for that is the disease organism gets into the
interior of the leaf.
The signs that we see - the white powdery growth on the
exterior of the leaf - is sporulation. By the time that happens,
the mycelium are all over the place inside the leaf. Where
Botrytis, on the other hand, is penetrating the leaf surface
but doesn't hide within the cells within the leaf. It's generally
penetrating from the outside in.
BOTRYTIS
When it comes to preventing Botrytis, get all of the debris
out of the greenhouse and, remove any foliage that isn't
healthy or isn't going to recover for any reason at all. It could
be as simple as everybody brushes up against one side of the
14 2022 GUIDE TO CANNABIS PRODUCTION
bench and those leaves or branches start to get bruised - get
them out of there.
Make sure the climate is managed in a way that you don't
have condensation occurring on foliage. The biggest point
to watch for is typically right at that point when we change
from day to night. So in a warehouse it's really abrupt. The
lights go up, the HVAC system is compensating and you hit a
point where the humidity goes up to where you can actually
condensate on the leaves.
" In a greenhouse, it's also going to generally be because of
swift environment change, " says Tami Van Gaal, CEA division
leader at Griffin. " But it's less about that exact moment
we transition from day to night and it's more just about
increasing humidity in the space over time. So growers need
to vent. If the humidity is too high outside to effectively vent,
you actually heat the greenhouse space and that will dry out
the air. "
POWDERY MILDEW
Powdery mildew is the more difficult foliar disease to detect
early and to control once it has been established in the crop.
When spores land on leaves and begin to grow, growers may
notice a slightly dull appearance, or slight change in color, as
mycelium develop across leaf surface.
The way that cannabis is typically grown can create a
high-humidity microclimate around the foliage. Add in tight
spacing with little room for air to get around the plant and you
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