The Heartbreak of Botrytis

Decay at the terminal portion of the flowering stem of
poinsettia, due to infection by Botrytis cinerea

Dark blotches are bract
infections by B. cinerea

On Monday, December 16th, we received a sample of poinsettias that for all commercial purposes had been ruined by Botrytis blight. Botrytis cinerea is a pernicious and ubiquitous fungus that particularly infects wounded or senescent tissue such as old flowers. From this foothold it can spread to other plant parts. When the fungus sporulates, the colors of the black conidiophores (spore-bearing threads) and white conidia (spores) combine to give the appearance of a gray mold. The spores are easily carried around on air currents.

Botrytis cinerea can wreak havoc with many different host species, even causing canker on rose canes and fruit rot on plants such as strawberry. More specialized species of Botyrtis also exist. One is Botrytis elliptica, which affects primarily lilies. Botrytis tulipae causes a disease called "fire" on - you guessed it - tulip.

Closeup of conidiophores and conidia of Botrytis cinerea,
growing on cyathia (true flowers) of poinsettia. Black bar = 1mm.

The Achilles heel of Botrytis is its need for abundant moisture. In greenhouses, care must be taken to ventilate, even for a while after sunset, in order to keep the relative humidity down. Watching watering practices (timing, drainage) is also important. Fungicides are sometimes needed. Another essential element in Botrytis management is prompt removal of dead plant material from the house. For more information on Botrytis in greenhouses, see our blog from May 18, 2012.

Pansy bed at NCSU in early 2012. Botrytis blight.

Be on the look out for Botrytis blight on pansies in the landscape, especially in the late winter and early spring. To prevent problems, avoid overhead watering if possible, and make sure the plant spacing and surrounding shrubbery allow for good airflow. For more information on Botrytis in the landscape, see the May 31, 2013 blog.

Light colored dead blotches on flowers, spreading to leaves,
are a hint that you might have Botrytis blight in your pansies.

Just a reminder to check our holiday closing schedule. We look forward to seeing you in 2014!

Mike Munster and Kelly Ivors

Sample of the Week: Botrytis Blight of Pansy

Botrytis Blight on Pansy (Photo: Mike Munster)

This week we received pansies from raised beds in a trial garden in Henderson County, North Carolina. The roots and crowns were in good condition but some of the flowers, flower stalks and leaves were decaying. The main symptom on leaves was a very watery rot. The fungus Botrytis cinerea was observed sporulating on some of the material when we received the sample. Sporulation was heavy after a day of moist-chamber incubation, as indicated by distinctive masses of gray spores. Making a diagnosis when Botrytis is involved can be tricky, because the fungus can be both a secondary invader and a primary pathogen. It often infects spent blooms and then moves into other parts of the plant. In this case it appears to be fairly aggressive, so Botrytis blight is the diagnosis.

Wet rot of pansy leaves caused by Botrytis (Photo: Mike Munster)

Stereomicroscope view of pansy flower stalk with sporulation from Botrytis cinerea
(Photo: Mike Munster)

For more information on Botrytis Blight, click here
Thanks to Mike Munster for this "Sample of the Week" submission.