PPDL Picture of the Week for
March 11, 2013

Botrytis Blight (Gray Mold)

Gail Ruhl, Sr. Plant Disease Diagnostician, Purdue University

Botrytis blight caused by Botrytis cinerea is one of the most common fungal diseases of greenhouse crops. The disease is often referred to as gray mold because it produces numerous gray fuzzy-appearing spores on the surface of infected tissue.  A variety of plants including ornamentals, vegetables and herbs are susceptible.  Management of environmental conditions, sound cultural practices and use of preventive fungicides will control this disease.

Fungal diseases such as gray mold can occur seemingly without warning and quickly cause widespread damage to plants. Botrytis gray mold can occur on flowers and buds of many greenhouse flower crops, and is sometimes associated with stem and leaf rots or other damage. Botrytis at first appears as a white growth on the plant but very soon darkens to a gray color. Smoky-gray dusty–like spores are produced in abundance on diseased lesions as well as on plant debris left on benches, the greenhouse floor and in trash containers. Spores are easily spread by air currents or in splashing water. In greenhouses, any activity will result in movement of spores. High humidity conditions favor the growth of Botrytis and disease development is rapid when plants are crowded and poorly ventilated.

An integrated approach, including sanitation, monitoring, environmental control and fungicides is desirable for successful management of Botrytis blight.

  • Sanitation is the first important step. Inspect plants frequently and carefully for disease symptoms and signs. Dead and dying tissues are easily colonized by Botrytis and the fungus then spreads to green, healthy tissues.
  • Remove and destroy dead and dying plant material. Significant gray mold control can occur by picking off and discarding dead leaves and spent flowers. Do not throw debris under benches or on walks.

  • Provide good spacing between plants.

  • Heat and ventilate greenhouses to prevent high humidity.
  • Avoid excessive splashing of water on foliage.
  • Use a labeled fungicide to prevent the spread of this fungus to healthy plants and plant parts; greenhouse populations of Botrytis rapidly develop fungicide resistance with repeated applications of fungicides with the same mode of action (FRAC Group) thus be observant of FRAC codes and rotate fungicide use accordingly. BP-71: Fungicide Rotations for Nursery, Greenhouse, and Landscape Professionals (pdf file)
  • Read and follow fungicide label directions before use. Some fungicides may be phytotoxic under certain conditions.

Click image to enlarge

Figure 1. Botrytis stem rot

Figure 2. Initial white sporulation of Botrytis on stem

Figure 3. Close-up of Botrytis sporulation

Figure 4. Typical grayish color of older Botrytis growth on rotted stem tissue

Photos courtesy of Tom Creswell, PPDL

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service