Botrytis on herbaceous perennials in 2013 season
Nursery and greenhouse growers have been challenged by recent cloudy and rainy weather to produce perennials and keep away Botrytis. Remembering cultural practices and correct fungicides will help until we get more sunshine.
The recent cool, dark, wet weather conditions along with perennials being in full flower in area poly houses and greenhouses can lead to Botrytis blight outbreaks. Crops like coreopsis, dianthus (Photo 1), heuchera, lavandul and rudbeckia can be especially vulnerable to this disease since they have a full flower canopy at this time.
Photo 1. Botrytis flower blight on dianthus. Photo credit: Cheryl Smith, Univ. of New Hampshire
Remember that botrytis is a fungus that can cause leaf spots, petiole blighting (Photo 2) and stem cankers on many different annuals and perennials. It will produce large masses of spores that are most often called “grey mold” (Photo 3). These spores or conidia will be spread on wind currents and can travel from infected to uninfected plants in that manner. The spores can live for upwards of 21 to 24 days before they germinate on a plant.
Photo 2. Botrytis on petiole of delphinium. Photo credit: Maria Tobiasz, Cornell Univ.
Photo 3. Botrytis sporulation close-up. Photo credit: Tom Creswell, Purdue Univ.
Michigan State University Extension suggests these cultural control practices that will reduce the conditions that favor Botrytis infections, including: reducing the relative humidity in the greenhouse or poly house below 85 percent; making sure plants do not remain wet for six or more hours in a 24-hour period; and if possible, heat and vent mornings and evenings for at least a half-hour or more to reduce humidity and keep plant surfaces dry.
If plants are infected and need to be removed from the growing area, do not just remove the plants and throw them on the compost pile out back as the spores can blow back into the facilities on wind currents. Bag up plants where they were growing, seal the bags and remove them from the facilities.
As for preventative fungicides, MSU plant pathologists recommend fungicides that contain the following active ingredients: chlorothalonil, fenhexamid, iprodione, pyraclostrobin + boscalid, cyprodinil +fludioxonil or polyoxin D zinc salt.
Apply any of the above mentioned products and be sure to have complete coverage and do not go longer than seven days between applications for your best results. Some of the above mentioned products may “spot” open flowers or leave a residue.