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UC Cooperative Extension Ventura County
669 County Square Dr. Suite 100
Ventura CA 93003
Phone: 805.645.1451
Fax: 805.645.1474

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Botrytis


With the late and often heavy spring rains, Botrytis gray mold has been an unusually severe problem. Rose flowers have in many instances been severely blighted. Jasmine, geranium plus other garden flowers and vegetables have also been affected. The disease on roses starts with small, red dots on the flower petals or a brown/beige edge on the petals. The red dots and/or the brown petal margins progress into the flower, often blighting the whole structure and even progressing down the stem. As browning progresses, a blackish-gray, fuzzy growth often appears on the necrotic tissues. This fuzzy growth is the Botrytis fungus. Once established, destruction of plant tissues can be very rapid.

Botrytis fungus is an excellent opportunist. Botrytis spores can invade almost any weak, dying or dead plant tissue and from that infection locus invade surrounding healthy tissues. Therefore, sanitation is an important part of disease control. Prune out dying and dead flowers. Shake or brush off plants to get spent petals to fall to the ground. Diseased plant parts should be placed in the green waste container for recycling, i.e. remove them from your landscape.

Fungicide sprays can be helpful to reduce Botrytis activity.

Besides causing problems for roses, Botrytis gray mold can attack many other plants in the garden. Geranium, gladiolus, jasmine, iris, lily, tulip, tomato, statice, hyacinth, magnolia, and other plants can be hosts for gray mold. There are also other diseases that may be present, but the presence of the dark gray, fuzzy fungus growth on the surface of blighted plant tissue is a good indication that Botrytis is the causal agent on the blighted plant.