Botrytis cinerea (Gray Mold)

IDENTIFICATION

"Grey mould, caused by the fungus Botrytis cinerea, is a very common disease, causing a growth of fuzzy grey mould. It infects many plants, especially those grown under glass where conditions are humid.  It normally enters through a wound or infects plants under stress, but will infect healthy plants as well, especially under humid conditions. It can be expected at any time of year.

Botrytis cinerea is an ubiquitous fungus, whose airborne spores are always present. It thrives as a saprophyte (a micro-organism living on dead organic material), but can also infect living plants under certain conditions. On green plant parts a wound or other stress is usually needed for infection, but on flowers and fruits it can infect without wounds, particularly under humid conditions.

It is also able to cause latent infections where the plant is infected but symptoms of the disease may not be produced for a considerable time. In some fruit crops the fungus enters flowers and colonises the developing fruit, but does not break out and cause a rot until the fruit begins to ripen and sugar content rises. This is very noticeable with strawberries. It can also cause latent infections in primulas, where research has shown the fungus is seed-borne and develops with the plant, only breaking out after considerable growth has occurred.

LIFE CYCLE

The fungus forms black, seed-like resting structures (sclerotia) in dead plant tissue which can carry the fungus through periods when host plants are scarce. These germinate to generate the sexual structures which in turn release a second, sexual, spore. These can initiate infections, but most of the damage is done by spread of the airborne, asexual spores (conidia) released from the fuzzy grey fungal growth.Royal Horticultural Society.

penn state gray mold Management Guidelines

Recommended controls for Botrytis cinerea (GRAY MOLD)

Each control will have its own set of parameters that will be best suited for individual environments. Certain controls may only be available for commercial application.

Commercial farmers are required to reference their own state laws to ascertain if the recommended controls fall within compliance of their states regulatory guidelines.

Biological Controls

Biological Controls of Botrytis Cinerea are the preferred methodology of management during the flowering stage.  Due to the sensitive nature of dense flowers absorbing moisture, it is recommended to first remove and dispose of the damaged plant matter, then spray with a very fine mist to prevent over-saturating the flowers with water.

commercial farmers - please be advised that heavily spraying certain bio-fungicides late in flowering may cause failed testing for micro-biological contamination.

CHEMICAL CONTROLS

Potassium Biocarbonate has shown only a small amount of success when dealing with gray mold.

Cultural, MECHANICAL AND PHYSICAL CONTROLS

  • Plant in a sunny location wherever possible
  • Keep humidity levels below 50%
  • Make sure there’s good air circulation (through plant spacing, pruning and ventilation)
  • Promote steady growth with moderate applications of nitrogen fertilizer (or use a time release fertilizer)
  • Remove and discard infected material, take special care in the fall to reduce the amount material available for over wintering (if applicable)

CHA RECOMMENDATIONS

MORE STUDIES TO ASCERTAIN IF FOLIAR SPRAYING BIO-FUNGICIDES SHOULD BE DISCONTINUED AFTER 4-6 WEEKS OF FLOWERING.

RESEARCH REGARDING THE USE OF MEDICINAL HERBS TERPENE PROFILES FOR ANTI-FUNGAL CONTROL, POSSIBLY FOCUSING ON SESQUITERPENES FOUND IN THYME, OREGANO, ROSEMARY, LAVENDER, EUCALYPTUS & CLOVE.

CHA TIPS:

•INSPECT ALL YELLOWING OR DECAYING LEAF TIPS

•KEEP HUMIDITY BELOW 50% WITH STRONG CIRCULATION

•PRUNE AND REMOVE AT LEAST 1 INCH BELOW THE INFECTED AREA

 

Selected References

Michigan State University Extension

Royal Horticultural Society

Penn State College of Agricultural Sciences

UC IPM Pest Management Guidelines: Grape UC ANR Publication 3448.  Authors: R. J. Smith, UC Cooperative Extension, Sonoma County
L. J. Bettiga, UC Cooperative Extension, Monterey CountyW. D. Gubler, Plant Pathology, UC Davis

Greenhouse evaluation of Bacillus subtilis AP-01 and Trichoderma harzianum AP-001 in controlling tobacco diseases