NC State Extension Publications

Pathogen

Botrytis gray mold is caused by the ubiquitous asexual fungus Botrytis cinerea (B. cinerea).

Host Crops and Plants

Botrytis affects many vegetable crops including tomato, pepper, bean, potato, onion, crucifers, and cucurbits as well as fruits, berries, and ornamentals.

Host Parts Affected

Botrytis can affect all aboveground plant parts of tomato in both the greenhouse and field. This fungus occurs as both a pathogen and a saprophyte causing diseases such as damping off, stem girdling, foliar blighting, and postharvest rots.

Identification

Botrytis produces a dense velvety gray brown spore mass on infected tissue which when disturbed releases a cloud of spores (Figure 1). Tomato leaf and stem lesions are tan to brown in color. Stem infections occur during periods of high humidity through leaf scars, cracks, and pruning wounds. Spores can remain dormant for up to 12 weeks within pruning leaf scars and are triggered to germinate during plant stress. Stem lesions may expand in concentric rings to girdle the entire stem causing wilting above the infection site. Flower petals are very susceptible and can initiate infection of pedicels and developing fruit. Fruit lesions are typically a whitish soft rot and often the skin ruptures near the center of the decayed area allowing spores to form on exposed tissue (Figure 2). Small 3-8 mm whitish rings on the fruit surface are aborted botrytis infections known as ghost spots which reduce market quality.

Botrytis on tomato stem

Figure 1. Botrytis infection on tomato stem, showing brownish-gray, dry lesion and girdling of the stem. Masses of gray colour Botrytis spores can be seen on the surface.

Shawn Butler, NCSU PDIC

Botrytis on tomato fruit

Figure 2. Botrytis infection on tomato fruit, showing rotted tissue and spores.

Shawn Butler, NCSU PDIC

Favorable Environmental Conditions for the Disease

  • High humidity and moisture (4-6 hours of free water from dew, rain, overhead irrigation or greenhouse condensation is sufficient for infection).
  • Cool to moderate temperatures (optimum growth 65-73°F).
  • In North Carolina Botrytis typically occurs after midseason in the field and during postharvest shipping. The disease can occur year round in greenhouse production.

Disease Transmission

Pathogen spores are transported via wind, rain and greenhouse air currents. The fungus survives/overwinters as mycelia or sclerotia in plant debris and organic soil matter. Various other crops nearby may serve as pathogen sources. Fallen flowers are a common source of leaf infections.

General Disease Management

  • Currently there are no known B. cinerea resistant tomato cultivars
  • Apply fungicides preventatively prior to dense canopy growth, rotate fungicides to manage resistance
  • Avoid overhead irrigation, minimize plant wetness
  • Do not work on wet plants, prune plants in the early afternoon allowing wounds to dry quickly
  • Ventilate greenhouses to maintain relative humidity at less than 90%
  • Temperatures above 70°F discourage Botrytis development
  • Practice good greenhouse sanitation, scout, bag, and remove infected plants

Disease Control for Conventional Growers

Botrytis gray mold of tomato can be controlled by using cultural practices, however, if disease pressure is high, fungicide sprays may be helpful to control disease. For the latest fungicide recommendations for gray mold see the Southeastern US Vegetable Crop Handbook. Fungicide labels are legal documents, always read and follow fungicide labels.


Example products for gray mold control in tomato:

Active ingredient Example product Pre-harvest Interval (day) Fungicide group
Boscalid Endura 0 7
Chlorothalonil + cymoxanil Ariston 3 M + 27
Difenoconazole + cyprodinilG Inspire Super 2.09SC 0 3 + 9
Fluxapyroxad + pyraclostrobin Priaxor 0 7 + 11
Potassium phosphite + chlorothalonil Catamaran 0 33 + M
DicloranG Botran 10 14
Chlorothalonil Bravo 0 M
G Can be used in greenhouses, see label for restrictions


Disease Control for Organic Growers

Gray mold can be successfully controlled using cultural practices as listed above.

Disease Control for Home Gardeners

Gray mold can be successfully controlled using cultural practices as listed above.

Useful Resources

Acknowledgements

The factsheet was prepared by the NCSU Vegetable Pathology Lab.

Author:

Associate Professor, Vegetable Pathology
Plant Pathology

Publication date: March 6, 2015

Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your county Cooperative Extension agent.

North Carolina State University and North Carolina A&T State University commit themselves to positive action to secure equal opportunity regardless of race, color, creed, national origin, religion, sex, age, veteran status or disability. In addition, the two Universities welcome all persons without regard to sexual orientation.