Published on 05/27/96

Long Winter Leads to Botrytis Blight in Landscape

The late-spring sun is cranking up the heat. It's hard to believe the long, cold winter is still causing problems in Georgia landscapes.

"We've had a lot of Botrytis blight in landscape plants this spring," said Jean Williams-Woodward, a plant pathologist with the University of Georgia Extension Service.

Botrytis blight is caused by a fungus, Botrytis cinerea, she said. Commonly known as "gray mold," it's the most common pathogen in any greenhouse, nursery or landscape. It attacks any aboveground part of many vegetable and landscape plants.

"Botrytis is always a problem for any flowering plant," Williams-Woodward said. "The problem this spring has been mostly in bedding plants. It hasn't been too bad in woody ornamentals."

The problem started, she said, in the state's greenhouses, mostly because of the winter that didn't want to end.

"Greenhouse growers had all these bedding plants ready to go, but it was still too cold," Williams-Woodward said. "They couldn't sell them."

Waiting for spring sales to rev up, growers wound up having to hold the plants a month longer than they normally would have. And the plants suffered from having to be held so long. Some flowers dropped off, and leaves yellowed.

Now the plants are in the landscape, where Botrytis is easier to control because the plants are more spread out. But it's still something to contend with.

Because the injured and yellowing tissues are more vulnerable, Williams-Woodward said Botrytis blight could be more of a problem in landscapes this year.

Botrytis attacks these old flowers and leaves and other weak tissues first, she said. Then it spreads into healthy tissue. On bedding plants, Botrytis often causes leaf spots when infected flowers drop onto leaves. It's most active under wet conditions and when the humidity is high and the air is stagnant.

Williams-Woodward said the fungus is easy to identify. With a magnifying glass, and often without it, she said, you can see a gray-brown web and grape-like clusters of spores on infected tissues.

"The spores are dry and are easily dispersed by air movement," she said. "Overhead watering and rain disperse the spores, too. The force of the water droplet landing on a leaf creates a shock wave that dislodges the spores into the air."

Splashing water droplets can carry the spores to nearby plants, too.

"Pick up a plant with Botrytis sometime and gently flick the infected plant part," she said. "A cloud of spores can usually be seen floating in the air above the plant."

Controlling Botrytis in the landscape takes a little cleaning up, using a fungicide and maybe changing a few things around your plants.

"Prune dead and injured stems from cold-damaged plants," Williams-Woodward said. "Clean the ground (and the inside of pots) of dead, fallen leaf litter. And remove yellowing leaves from the base of plants."

People who pay regular attention to their plants can prevent the spread of the fungus. Picking off and discarding spent flowers and yellowing leaves as they show up will often keep plants healthy.

You may need to space your plants farther apart, too, to allow for better air circulation. If Botrytis is a problem, don't use overhead irrigation, she said.

Because the fungal spores spread around so easily, fungicides can be important in controlling Botrytis.

"Spray a protective fungicide after the plants are free of blighted tissue," Williams-Woodward said. "Consult your county agent to find out which fungicide to use for a particular plant."

Dan Rahn is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.