Professional Marijuana Grower March-April 2018 Issue | Page 28

stagnant environment, which is depleted of much of
its dissolved oxygen content, is perfect for pythium.
Put another way, overwatering is a common cause of
pythium. Pythium is also common in hydroponic systems
that have an insufficient amount of dissolved oxygen in
the nutrient solution.
The first signs of pythium can mimic a nitrogen defi-
ciency, with the lower leaves turning yellow. Eventually
these leaves may also have brown spots, again mim-
icking other nutrient deficiencies. The entire marijuana
plant will ultimately appear wilted and, in extreme
cases, will die. Upon inspection of the roots, a marijua-
na grower can quickly identify pythium. Brown, slimy
roots are a dead giveaway that pythium lurks in the
grow room.
Pythium Prevention and Treatment
If caught early enough it is possible to recover from
a pythium attack. There are many oxygen boosting
additives available in hydroponic stores. Diluted hy-
drogen peroxide is one way growers can increase the
dissolved oxygen content, but it should be used spar-
ingly. A hydroponic grower must maintain a consistent
temperature of 65-70 degrees F in the reservoir. When
the temperature of the water rises, the dissolved oxygen
content decreased. Pythium is notorious for showing
up in hydroponic systems when the water temperature
28 • Professional Marijuana Grower
reaches above 75 degrees F. Hydroponic gardeners
can use a water chiller to maintain temperatures in the
desired range.
Powdery Mildew
Powdery mildew is another common pathogen that
causes trouble for cannabis growers. Powdery mildew
spreads quickly and can destroy a healthy garden in a
matter of days. Powdery mildew can be detected by a
white, powdery coating on leaves and shoot tips. This
fungus spreads fast via airborne spores.
Powdery Mildew Prevention and
Treatment
Powdery mildew is a fungus that can only thrive
when the atmospheric conditions are right. Keeping
temperature and humidity levels in check are the best
preventative measure against powdery mildew. Air
filtration devices on the ventilation system’s intakes are
also a good way to reduce the likelihood of powdery
mildew. If powdery mildew is contracted, sulfur burners
or organic-based fungicides can be effective during the
vegetative and early stages of flowering. Treating a
powdery mildew outbreak in the late stages of flower-
ing can be very difficult for a cannabis grower. Most of
the time, when contracted in the later stages of flower-
March/April 2018