Botrytis Blight
Causal Agents
Botrytis cinerea
Botrytis spp.
Hosts
Large host range of herbaceous plants. Some hosts include:
Azalea, Chrysanthemum, Delphinium, Geranium, Hosta, Hydrangea, Iris, Lilium, Rhododendron, Rose, Rudbeckia, Viola
Symptoms & Signs
When Does it Occur?
Botrytis blight is most common on weakened or stressed plants. Spores are transported via wind and water droplet impact. Fungal spores require 6 or more hours of continuous leaf wetness or humidity >90% for germination. Generally, botrytis blight is favored by moderate, humid weather and therefore is most problematic in the landscape during late fall and early spring. However, disease can occur anytime of year given sufficient leaf wetness. In greenhouses, botrytis blight can occur year-round.
Cultural Management
Practice proper sanitation practices and reject any clearly infected nursery stock. Remove and dispose of old, decaying plant material as Botrytis can survive and produce more inoculum on these decaying materials. Infected material should be disposed of by burning or burying beneath the soil. Avoid overhead irrigation where possible. Prune canopies and space plants far enough apart to promote proper airflow and drying.
Chemical Management
Fungicide applications are only effective when applied preventatively. Once symptoms have been observed, an epidemic is very difficult to control with fungicides. Due to the prolific reproduction and spore formation of Botrytis fungi, they are quick to develop fungicide resistance. There are already many populations resistant to multiple fungicides. Always rotate fungicide modes of action between each application to avoid the development of resistant populations. If you suspect you have a resistant population, some University and independent diagnostic clinics provide fungicide resistance screening services.
Selected fungicides for botrytis blight management
| Active Ingredient(s) | Trade Name(s) | Application Timing | REI (h) | Efficacy Rating | FRAC Code(s) | Resistance Risk |
|---|---|---|---|---|---|---|
| Azoxystrobin | Heritage, Strobe | P + C | 4 | ++ | 11 | H |
| Benzovindiflupyr | Mural | P + C | 12 | +++ ? | 7 | M |
| Boscalid | Pageant | P + C | 12 | +++ | 7 | M |
| Chlorothalonil | Chlorothalonil, Concorde, Daconil, Mainsail | P | 12 | ++++ | M5 | L |
| Copper compounds | Badge, CuPRO, Grotto, Phyton | P + C | 4-48 | ++ | M1 | L |
| Cyprodinil | Palladium | P + C | 12 | +++ | 7 | M |
| Fenhexamid | Decree | P + C | 12 | ++++ | 17 | L-M |
| Ferbam | Ferbam | P | 24 | + | M3 | L |
| Fludioxanil | Emblem, Medallion, Spirato | P | 12 | +++ | 12 | L-M |
| Fluopyram | Broadform | P + C | 12 | +++ ? | 7 | M |
| Fluoxastrobin | Disarm, Fame | P + C | 12 | ++ ? | 11 | H |
| Hydrogen dioxide + peroxyacetic acid | TerraClean, ZeroTol | P | 0 | + | Not classified | L |
| Iprodione | 26GT, Chipco 26019, Ipro | P + C | 12, 24 | ++++ | 2 | M-H |
| Isofetamid | Astun | P + C | 12 | +++ | 7 | M |
| Mancozeb | Dithane, Fore, Mancozeb | P | 24 | +++ | M3 | L |
| Maneb | Maneb | P | 24 | + | M3 | L |
| Metconazole | Tourney | P + C | 12 | +++ | 3 | M |
| Neem oil | Neem Oil, Triact | P | 4 | + ? | Not classified | L |
| Polyoxin D | Affirm | P + C | 4 | +++ | 19 | M |
| Potassium bicarbonate | Armicarb, Kaligreen, MilStop | P | 4 | ++ ? | Not classified | L |
| Pydiflumetofen | Postiva | P + C | 12 | +++ | 7 | M |
| Pyraclostrobin | Empress, Insignia | P + C | 12 | ++ | 11 | H |
| Thiophanate-methyl | 3336, T-Storm, AllBan, SysTec | P + C | 12 | +++ | 1 | H |
| Thyme oil | Guarda | P | 0 | + ? | Not classified | L |
| Trifloxystrobin | Compass | P | 12 | ++ | 11 | H |
| Triticonazole | Trinity, Trinity TR | P + C | 12 | +++ ? | 3 | M |
1 Not all commercially available trade names are included to save space. Some products may have use restrictions. Always follow label directions for rates and use sites. Mention of specific products does not constitute endorsement.
2 P = Preventative; C = Curative
3 REI = Restricted Entry Interval
4 Relative efficacy. + = Marginally effective; ++ = Moderately effective; +++ = Effective; ++++ = Very Effective; ? = Limited information at this time.
5 Fungicide Resistance Action Committee code(s). Products sharing a code contain active ingredients with the same mode of action. Always use resistance management practices.
6 Resistance Risk: L = Low; M = Moderate; H = High, U = Unknown
