Gray mold (Botrytis) on hemp is so bad now, it was even featured on the front page of the local paper (A new kind of harvest: Hemp grower battles mold, designs innovative processes).

The weather this fall has been ideal for development of molds in the tight colas of the hemp plant. The alternating cool and moist weather followed by a few clear days of moderate temperatures have been perfect for the moisture-loving fungus. Which translates to bad news for the growers, who depend on the flowers for their CBD-related products.

Botrytis is omnivorous and is widely distributed in the environment. It is one of the hard-working decomposers of the plant world, but has the bad manners to attack plants not quite ready to be decayed.

Application of topical general purpose fungicides won’t touch the fungus deep within the overlapping tissues of the flowers. The best means is prevention, which right now isn’t too helpful. Plant breeders take note: an early maturing variety that will flower at our latitude and be harvested before the rains hit would be golden!

For more on this disease, see the PNW Plant Disease Management Handbook. The Oregon Department of Agriculture maintains a list of pesticides that are not prohibited for use on hemp.