Cause The following fungi or fungus-like microorganisms, Pythium spp., Phytophthora spp., and Rhizoctonia solani, attack young seedlings of many vegetables including tomato. Seedlings are susceptible to infection before or after emerging from soil. If seedlings are affected before emerging, it appears as poor germination. If the decay is after emergence, seedlings that fall over or die are said to "damp-off." The disease's destructiveness depends on environmental conditions and the amount of fungus in the soil. Cool, cloudy weather, wet soil, compacted soil, high humidity, and overcrowding are especially favorable to damping-off. Poor ventilation in greenhouses and contaminated soil or equipment also favors damping-off.
Symptoms Young seedlings develop a sunken, necrotic lesion near the soil line. If the lesion girdles the stem, the seedling collapses and soon dies. Also, seeds simply may not emerge.
- In the greenhouse or seedbed, pasteurize the soil with heat. For example, most pathogens die if soil is heated to 158°F (70°C) for 30 min. with aerated steam.
- Use raised beds to improve soil drainage, and avoid excessive irrigation.
- If damping-off occurs, stop watering for a while. Allow soil to dry somewhat around the plants. If the seedlings are in flats or in cold frames, give them as much air and light as possible.
- Use good sanitation in greenhouses.
- Seed treatment with one of the following fungicides.
- Apron XL at 0.085 to 0.64 fl oz/100 lb seed plus a dye to control Pythium spp. See label for reentry restrictions.
- Dynasty at 0.10 to 0.38 fl oz/100 lb seed plus a dye. 4-hr reentry.
- Maxim 4FS at 0.08 to 0.16 fl oz/100 lb seed plus a dye. To control pathogenic Fusarium and Rhizoctonia spp. 12-hr reentry.
- Thiram 50WP Dyed at 6 oz/100 lb seed (not labeled for Oregon) or 42-S Thiram at 6 fl oz/100 lb seed plus a dye. See label for reentry restrictions.
- Aliette WDG at 2.5 to 5 lb/A in at least 10 gal water/A on 7- to 14-day intervals to control Pythium. Use sufficient water to wet the entire plant canopy. Do not apply within 14 days of harvest. Do not combine with copper products. 24-hr reentry.
- C-O-C-S WDG at 1 lb/A. Do not apply through any irrigation system. 48-hr reentry. .
- Orondis Gold (Group 49 + 4) at 28 to 55 fl oz/A as an in-furrow, transplant water or banded soil application at planting. May be applied through drip after emergence. Preharvest interval is 7 days. 48-hr reentry.
- Regalia at 1 to 2 quarts/A as an in-furrow treatment. Does not benefit from the addition of an adjuvant. 4-hr reentry. O
- Ridomil Gold SL at 1 to 2 pints/A as a broadcast or band, to control Pythium. Do not use for greenhouse crops. Rotation crop restrictions apply; see product label for details. 48-hr reentry.
- Actinovate AG at 3 to 12 oz/A as a soil drench at planting. 1-hr reentry. O
- Actinovate Lawn & Garden at 1/2 to 1 teaspoon/gal water. H O
- Cease at 4 to 8 quarts in 100 gal water applied to soil at 1 pint/sq ft for each 3-inches of soil depth on 21- to 28-day intervals. For greenhouse plants only. 4-hr reentry. O
- Double Nickel LC at 0.5 to 4.5 pints/A for soil application on 14- to 28-day intervals. Can be applied the day of harvest. 4-hr reentry. O
- Mycostop at 0.07 oz/lb seed or Mycostop Mix at 0.05 to 0.08 oz/lb seed. 4-hr reentry. O
- Prestop as a soil drench or incorporation into growing medium. 4-hr reentry. O
- Rootshield Home and Garden at 1 to 3 Tbsp/gal water as a soil drench at planting. H O
- Rootshield WP at 3 to 5 oz/100 gal water for greenhouse soil drench and field chemigation or at 16 to 32 oz/A as an in-furrow spray. 0-hr reentry. O
- SoilGard 12G at 0.5 to 10 lb/A at 4-week intervals will suppress Pythium and Rhizoctonia. See label for specific application types and timings. Can be applied on the day of harvest. O
- Stargus at 6 to 8 fl oz per 1,000 ft row as an in-furrow treatment, or 3 to 4 quarts/A as a soil drench (drip or chemigation) on 10- to 21-day intervals. Preharvest interval is 0 days. 4-hr reentry. O
- Taegro ECO at 2.6 to 5.2 oz/A on 7- to 14-day intervals can suppress soilborne diseases. 24-hr reentry. O
- Tenet WP at 2.5 to 5.0 lb/A at sowing will suppress certain fungal pathogens including Fusarium, Rhizoctonia, and Pythium spp. See label for specific application types and timings. 1-hr reentry. O
Reference Gabor, B., and Wiebe, W. 1997. Tomato Diseases: A Practical Guide for Seedsmen, Growers and Agricultural Advisors. Saticoy, CA: Seminis Vegetable Seeds, Inc.