Cloudy, rainy weather, cool nights and greenhouses full of plants provide an ideal environment for Botrytis. Botrytis symptoms may include leaf spots, flower blights, bud rots, stem cankers, and stem and crown rots and can be mistaken for other causes.
Botrytis was recently diagnosed on pansy blossoms throughout a greenhouse. Symptoms (see photos) appeared as tannish irregular spots on flower petals which eventually enlarged into larger areas. The rest of the plant did not symptoms. In this case, plants were overwatered going into a cold, cloudy day and the greenhouse was not well ventilated. To manage the problem, infected blossoms were removed and put in a covered trash can to reduce sporulation, and the greenhouse was ventilated to reduce humidity. (During cool days, heating the greenhouse air a few degrees and then venting will lower the relative humidity.) HAF fans were used to move air so there was less condensation and employees were trained to water early in the day to allow foliage and flowers to dry quickly.
The Rutgers IR 4 Ornamental Horticulture Program review of the literature on Botrytis Blight on various crops in 2014, reported the following products provided excellent efficacy in numerous experiments:
- Pageant (pyraclostrobin plus boscalid)(FRAC codes 7 & 11)
- Daconil (chlorothalonill) (FRAC code M5)
- Palladium (cyprodinil & fludioxonil)(FRAC codes 9 & 12)
- Decree (fenhexamid) (FRAC code 17)
In addition, Affirm (polyoxin D) (FRAC 19), Heritage (azoxystrobin)(FRAC code 11), Medallion (fludioxonil) (FRAC code 12) and Compass (trifloxystrobin) (FRAC code 11) showed good to excellent efficacy in a number of experiments.
New fungicides such as Mural (azoxystrobin)(FRAC code 11) and benzovindiflupyr (FRAC Code 7), and Orkestra (fluxapyroxad)(FRAC code 7) and pyraclostrobin (FRAC code 11) are also reported to do well in research reports by Ann Chase.
Be sure to rotate among effective products with different active ingredients to prevent resistance development. The FRAC (Fungicide Resistance Action Committee) code on the product label denotes the active ingredient group(s) found in the product. Some Botrytis populations have developed resistance to certain fungicides. There are reports of resistance to the fungicides containing thiophanate methyl (FRAC group 1), iprodione (FRAC group 2) and fenhexamid (FRAC group 17). Avoid making more than two consecutive applications of the same fungicide or group of fungicides.
Some OMRI listed organic fungicides labeled for Botrytis include: Actinovate SP (Streptomyces lydicus), Cease (Bacillus subtilis), Cease/Milstop (Potassium bicarbonate) tank mix, and Triathlon BA or Double Nickel (Bacillus amyloliquefaciens). These products must be used preventatively but can be part of your resistance management plan.
Read labels carefully for plant safety precautions for some fungicides may leave spray residue or damage flowers. For example, Pageant and Orkestra can cause discoloration of tender impatiens and petunia flowers. Decree can leave a slight residue which may be visible after the spray solution dries. Follow the directions on the fungicide label to prevent plant injury. It is also best to heat and vent first, if you are seeing fungal sporulation. Spraying or watering can disseminate the spores.
Tips on Preventing Botrytis During Cool, Cloudy Weather Periods, UConn Extension
Chase A. New Fungicides for Ornamentals
Some Fungicides Labeled for Herb Bedding Plants, UConn Extension
Some Fungicides Labeled for Vegetable Bedding Plants, UConn Extension
Fact Sheet: Reducing Humidity in the Greenhouse.
Photos: Botrytis on pansy blossoms
Spray residue (Decree) on pansies
More photos in photo library (stem cankers, fuzzy spores)
Tina Smith, Geoffrey Njue, UMass Extension
with input from Leanne Pundt, UConn Extension
originally posted 4/16 updated 4/17