Botrytis / Gray Mold

Botrytis cinerea species complex

Botrytis gray mold is a broad-host-range disease of flowers, vegetables, berries, grapes, herbs, and greenhouse ornamentals. Botrytis cinerea commonly colonizes senescent petals, wounded tissue, and dead leaves, then invades adjacent healthy organs under cool to moderate, humid conditions. The defining sign is a dusty gray-brown mass of branched conidiophores and spores on blighted tissue, though early lesions may be water-soaked without visible mold. Blossom blight, stem cankers, fruit rot, damping of cuttings, and postharvest decay can occur. Dense canopies, condensation, prolonged wetness, dead petals, and wounded produce drive outbreaks.

Identification

Search humid interior canopies, spent flowers, and fruit-contact points for soft tan lesions and gray fuzzy sporulation. Botrytis spores detach as a visible cloud when disturbed, but avoid deliberately aerosolizing them. Sclerotia may form as hard black structures on dead tissue. Submit fresh lesion margins and attached sporulating tissue in a rigid container, plus whole flowers or fruit when affected. Culture and microscopy usually support diagnosis, although B. cinerea may colonize tissue already killed by chilling, chemical injury, or another pathogen. Differentiate from Rhizopus and Mucor soft rots, Sclerotinia white mold, Rhizoctonia web blight, bacterial soft rot, downy mildew, and ethylene or cold injury.

Symptoms / Signs

Flowers develop tan flecks, blight, and collapse; infected petals may adhere to leaves and initiate secondary spots. Leaves show irregular water-soaked to brown lesions. Stems and petioles can develop pale or brown cankers that girdle shoots. Fruit becomes soft, tan to brown, and covered with gray spores, sometimes after an apparently clean harvest because infections were latent. Seedlings and cuttings may rot at wounds or senescent leaf bases. Gray sporulation is most abundant after a humid night.

Life Cycle / Process

Botrytis survives in crop debris, mummified fruit, sclerotia, and asymptomatic plant tissue. It produces enormous numbers of airborne conidia that settle throughout production areas. Infection often begins on senescent or wounded cells, then advances into healthy tissue. Free moisture, condensation, and high relative humidity permit germination; cycles repeat rapidly in enclosed canopies. Latent blossom or fruit infections can activate during ripening, shipping, or cold storage breaks.

Prevention

Remove dead flowers, leaves, and fruit before they sporulate. Space plants, ventilate greenhouses, use horizontal airflow, prevent overnight condensation, and irrigate early without wetting flowers. Sanitize benches, harvest containers, and cutting tools. Handle fruit gently and maintain an uninterrupted cold chain appropriate to the commodity. Use resistant or open-canopy cultivars where available. Preventive fungicides may be needed in high-value crops, but resistance is common and cultural control is indispensable.

Management / Control

Isolate affected lots and remove sporulating material in closed bags while foliage is dry. Lower humidity, increase air exchange, and correct leaks or irrigation schedules immediately. Cull rotted fruit and sanitize packing surfaces. Where labeled fungicides are justified, rotate FRAC groups and avoid repeated use of products with known cross-resistance; confirm crop, site, and preharvest interval. Biological products may suppress infection when used preventively but will not restore necrotic tissue. Investigate hidden sources such as spent petals, floor debris, and unrefrigerated harvest delays.

Procedure Steps

1. Inspect flowers, inner canopies, wounds, and fruit-contact points early in the day for gray sporulation. 2. Photograph signs without blowing on or shaking tissue; document condensation and humidity patterns. 3. Collect fresh lesion margins and intact sporulating organs in rigid, labeled containers and keep cool. 4. Remove affected material, sanitize work surfaces, and immediately correct condensation, wet flowers, and dead-tissue accumulation. 5. Use a crop-labeled resistance-managed protection program only for healthy at-risk tissue, then verify control through repeated scouting.

Safety Notes

Botrytis spores can aggravate respiratory allergies and occupational asthma. Avoid aerosolizing dry sporulation; use gloves, eye protection, and suitable respiratory protection for heavy cleanup. Discard decayed food crops and follow pesticide PPE, reentry, and preharvest requirements.