In the world of fungi, powdery mildew is unique, and controlling it can prove tricky for commercial cannabis growers.
Powdery mildew spores don’t require standing water to germinate, only brief periods of high humidity.
Day and night temperatures should not fluctuate more than about 15°F.
Wall-mounted fans help to disperse the spores, and employees that brush up against the plants will inadvertently carry the spores to new spots in the grow room.
It may be impossible to eliminate powdery mildew spores from the environment, but at least growers can make it more difficult for infections to take hold.
The application of products containing potassium bicarbonate will temporarily drop leaf surface pH, while products that contain sulfur will raise it.
Still, it is translaminar, meaning that if sprayed on the top of the leaf surface, the bottom of the leaf will be protected as well.
However, new plant growth is not protected, so the product must be reapplied on a seven- to 14-day schedule.
Most indoor cultivation sites do not circulate air between individual rooms, but even closed-loop ventilation systems can perpetuate powdery mildew outbreaks by dispersing spores throughout the grow room.
But if none of the previous four recommendations are followed, it’s unlikely that an outbreak will improve through leaf removal alone.
Furthermore, if the defoliation is extreme, the mildew will spread to the only part of the plant that remains to be infected — the flowers.
Maintaining a crop that is heavily infested with powdery mildew will place the rest of the cultivation facility at risk.
Ryan Douglas is the founder of Ryan Douglas Cultivation, LLC, which helps new cannabis cultivation businesses come to market quickly and spend less money getting there.