Canada (ON): Botrytis bumming you out?

With the intense period of rain we just had, and with more rain coming on Friday, it’s time to think about Botrytis control and prevention. One of the most common and destructive diseases of greenhouse crops, outbreaks usually follow periods of cool, damp, cloudy weather. Unfortunately, I can’t order up more sun for you, but I CAN suggest some management tactics.

by Sarah Jandricic, Greenhouse Floriculture IPM Specialist, OMAFRA

Seedling Blight caused by Botrytis in Geranium.

What is Botrytis?
Estimated to cause more economic loss in ornamentals than any other disease, this fungus has many common names, including blossom blight, bud rot, stem canker, stem and crown rot, cutting rot, leaf blight, and damping-off or seedling blight. Although there are over 50 different pathogenic species of Botrytis, in floriculture, Botrytis cinerea has the largest host range, and is most likely the one you’re dealing with.

Unfortunately, Botrytis cinerea has an extremely wide host range. Flowers with thick succulent petals, such as begonias, peonies and geraniums, are particularly susceptible. The disease also commonly affects African violet, dahlias, pansy, snapdragon, zinnia, chrysanthemum, and many others.

Grey mold on geranium: notice the characteristic “V” shaped lesion on Botrytis infected leaves. Photo courtesy of OSU.

How Do I know I Have it?
Botrytis can cause different symptoms on different kinds of plants, so you may need to confirm your diagnosis by sending samples to Guelph Lab Services. However, Botrytis infection usually begins as brown to gray circular spots that appear water-soaked regardless of the tissue affected. Later, tan to gray fuzzy mold develops on rotted tissue under humid conditions.

Generally, Botrytis attacks tender tissues (flower petals, buds, or seedlings), weakened or injured tissues, and aging and dead tissues. Actively growing tissues (e.g. healthy leaves) are seldom invaded, unless dead, infected tissue touches them directly.

How Does it Spread in the Greenhouse?
Botrytis cinerea persists in the greenhouse year as resting spores on living or dead plants, or in infested soil (which is one reason it’s important to always use new potting mix and sterilize pots appropriately). When the environment is right (i.e. temperatures around 15 C with >90% RH), the resting spores will germinate into active spores, called “conidia”. Conidia are dust-like, and can be easily dispersed in large numbers by air currents to new plants or overhead watering.

Botrytis conidia on Geranium. Photo courtesy of G. Barron, University of Guelph.

Read more at ONfloriculture