Gray Mold


Gray Mold
by Rob Sproule

Most fuzzy things are just plain cute. Who can resist an over-plushed teddy bear or a fuzzy caterpillar in the palm. This article is about one fuzzy thing that’s more hideous than adorable and rears its repulsive head during cool, wet summers. It’s Botrytis, or Gray mold, and it’s a wet-summer scourge.

Gray mold is a fungal super-villain. It grows quickly, can pop up virtually anywhere plants are grown, and can kill quickly if not dealt with promptly. It takes hold in cool, damp weather and invades damages plants first (be on guard after a hail storm or freak frost).

Identification and Damage

Molds are like a plant flu. While healthy plants can usually fight them off, sickly or damaged plants (ie. with exposed wounds), are easily invaded by roving spores.

Infected plants are often already dying (ex. gangly bedding plants during a wet August). One of the most common afflictions, gray mold first appears as a white growth but quickly turns to a smoky gray. On fruit or across rotting leaves in the soil, the fungus erupts into dusty gray, “˜fuzzy’ spores that can be spread with a puff of wind or a drop of rain.

It infects opportunistic food sources, like open wounds, rotting flowers or overripe fruit. From here it spreads quickly to healthy tissue. Depending on the plant it’s infecting, it will often start as brown spots on the leaves and spread rapidly across the plant. This is how it kills lilies, one of its favourite victims.

Prevention and Control

Gray mold its like trench-foot: it happens when tissue stays wet for a long time. If Botrytis sets in, the first critical step is to remove all infected tissue (and quickly). If that is just overripe strawberries or grapes, you’re in luck, but it’s often the entire plant that needs to be removed and thrown in the garbage (not the compost).

The pathogen is highly infectious, so wrap infected plants in a plastic bag as you remove them. Carrying them across the garden will leave spores behind you like breadcrumbs. Disinfect your hands before handling any other plants.

Clean all leaf litter and bits of decaying gunk out from around the infection. Clear off the ground and, if lower leaves of nearby plants are preventing the ground from drying up, prune off lower leaves to open more air circulation. Pick up old flowers and decaying leaf little in the fall and spring (it will seem overwhelming the first time but quickly gets easier).

Cut back on watering. Way back. Gray mold happening means that areas of your beds are never drying out, and chances are there’s enough rain falling that you need little or none supplemental watering. Check to see if you have automatic sprinklers that you’ve forgotten about (it happens more than you think).

After you clean up the ground down to soil level, prune out bottom foliage and stop watering, the area should start to dry out. Let it dry significantly before watering again, and when you do water only do it in the morning. Wet leaves + cool nights = perfect mold conditions.

Chemical treatments, which should be reserved for major outbreaks, typically employ copper or sulphur, which we’ve been using as an anti-fungal for eons, as their active ingredients. They’re desiccants, sucking the moisture out of the areas they touch and thereby starting the botrytis of the conditions it needs.


Read through our Growing Guides for tips to enrich your garden! 

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