See:
Tomato (Lycopersicon esculentum) - Gray Mold (Ghost Spot)
Cause The fungus, Botrytis cinerea (teleomorph: Botryotinia fuckeliana), is an opportunistic pathogen with a wide host range that easily invades stressed, damaged, or senescing tissue. All aboveground portions of the potato plant can be attacked but often disease starts on senescing flowers or damaged leaves. Air-blown spores (conidia) are produced throughout the growing season under a wide range of temperatures and humidity. Flower and stem infections are inoculum sources for disease spread within a field. Cool temperatures (65°F to 75°F is optimal but the fungus can grow between 50F° and 80°F), high humidity, and free water on plant surfaces favor the disease, as do close plant spacing and irrigation practices that keep plants wet for a longer time. Durable sclerotia overwinter in soil.
Symptoms Initially, small, water-soaked spots develop on leaves. Leaf spots enlarge into irregular brown areas and long brown streaks form on petioles and stems. Secondary pathogens may gain ingress, resulting in breakdown of stems. Dark-gray spore masses form on infected tissues.
Cultural control
- Promote healthy plant growth and minimize stress and plant injury.
- Remove dead or infected plant parts such as flowers and foliage.
- Time overhead irrigation to allow plants dry faster.
Chemical control
- Chlorothalonil (Group M5) products such as:
- Bonide Fung-onil is available for home gardens. H
- Bravo Ultrex at 0.7 to 1.36 lb/A or Bravo Weather Stik at 0.75 to 1.5 pints/A on 7- to 10-day intervals. Preharvest interval is 7 days. 12-hr reentry.
- Echo 720 at 0.75 to 1.5 pints/A on 5- to 10-day intervals. Preharvest interval is 7 days. 12-hr reentry.
- Echo 90 DF at 0.625 to 1.25 lb/A on 5- to 10-day intervals. Preharvest interval is 7 days. 12-hr reentry.
- Carboxamide (Group 7) formulations are registered for use. Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action (non-Group 7).
- Endura at 2.5 to 4.5 oz/A on 7- to 14-day intervals. Preharvest interval is 10 days. 12-hr reentry.
- Fontelis (SLN OR-220004; SLN ID-220007; SLN WA-220003) at 10 to 24 fl oz/A on 7- to 14-day intervals. Preharvest interval is 7 days. 12-hr reentry.
- Vertisan at 14 to 24 fl oz/A on 7- to 14-day intervals. Preharvest interval is 7 days. 12-hr reentry.
- Copper (Group M1) products offer limited control.
- Badge SC at 1 to 4 pints/A on 5-day intervals. Preharvest interval is 0 days. 48-hr reentry.
- Bordeaux 8-8-100. H
- Champ Formula 2 Flowable at 0.66 to 2.66 pints/A on 5- to 10-day intervals, starting when plants are 6 inches high. Suppresses Colorado potato beetle populations. 48-hr reentry.
- C-O-C-S WDG at 1.5 to 4.9 lb/A. 48-hr reentry.
- Cueva at 0.5 to 2 gal/100 gal water on 7- to 10-day intervals. May be applied on the day of harvest. 4-hr reentry. O
- Cuprofix Ultra 40 Disperss at 0.75 to 3 lb/A on 7- to 10-intervals. 48-hr reentry.
- Kocide 2000 at 0.75 to 3 lb/A on 10- to 14-day intervals. 48-hr reentry.
- Liqui-Cop at 1.5 to 2 teaspoons/gal water. H
- Previsto at 1 to 3 quarts/A on 7- to 10-day intervals. 48-hr reentry. O
- Luna Tranquility (Group 7 + 9) at 8 to 12 fl oz/A on 7- to 14-day intervals. Do not make more than two (2) applications before alternating to a fungicide in different FRAC groups (non-Group 7 and non-Group 9). Preharvest interval is 7 days. 12-hr reentry.
- Mancozeb products (Group M3) such as Dithane F-45 Rainshield, Gavel 75 DF or Ridomil Gold MZ (Group 4 + M3) ; see label for rates and intervals. Do not apply within 14 days of harvest. 24-hr reentry for Dithane F-45 Rainshield and 48-hr reentry for Gavel 75 DF and Ridomil Gold MZ.
- Scala SC (Group 9) at 7 fl oz/A on 7- to 14-day intervals. Use only in a tank-mix with another effective fungicide. Do not apply within 7 days of harvest. 12-hr reentry.
- Trilogy at 0.5% to 1%. Not labeled for use in Oregon. Do not use above 90°F or when plants are under heat or moisture stress. Do not use when foliage is wet as good coverage is essential. Poor control as a stand-alone product. 4-hr reentry. O
Biological control
- Stargus at 2 to 4 quarts/A plus a nonionic surfactant on 7- to 10-day intervals. Preharvest interval is 0 days. 4-hr reentry. O