Botrytis cinerea, or gray mold, affects many herbaceous plants, posing a particular problem to those grown in greenhouses. In the field, vegetables, including peppers, may be vulnerable to gray mold after prolonged periods of fogs, heavy dews, overcast skies or light drizzly rains. The mold can affect peppers anywhere in the world, according to “Vegetable Diseases: A Color Handbook.”
Young stems and leaves collapse suddenly, and gray spore masses and thread-shaped growths occur on the dead tissue. The fungus may also grow on flower petals and spread onto developing fruit. Spots expand into yellow or grayish lesions.
Examine any brown or spotted plant material on the peppers. Look for spore masses, gray in color, on dead or dying tissue. Some species of gray mold form tiny black structures called sclerotia that may be seen on dead plant tissue in late summer.
Handle pepper seedlings carefully. The fungus infects plants through wounds, such as cracks in the stem, as well as dying foliage, making it important to clear plant debris out of the garden.
Some species of gray mold form sclerotia, which can overwinter in woody stem debris, according to Cornell University and University of Florida websites. The sclerotia germinate in the spring or mycelium grows out of infected debris and develops infectious spores, called conidia. The spores may be windborne or splashed by rain to create new infections. Infections begin in the spring and spread during wet or very humid weather.
Water plants early in the day so the leaves can dry before sundown. Carry a paper bag when inspecting your pepper plants. Remove blighted pepper leaves or entire plants at the base and place them in a bag so they can be discarded or burned. Remove clipped seedlings from the seedbed and yellowish plant tissues. Spray fungicide if spring weather stays cool and wet or if gray mold was a problem the previous year. In greenhouses, maintain relative humidity under 80 percent and keep the greenhouse temperature higher than the outdoors temperature to avoid dew on the leaves. Use fans or opened doorways to circulate the air. In gardens, plant the peppers in well-drained soil and avoid over-fertilizing with nitrogen.
Cold, rainy springs and summer weather around 60 degrees Fahrenheit favor infection by gray mold, according to horticulturalists at Cornell University. The disease can also develop in temperatures from 65 to 65 degrees, according to the University of Florida.