Cause Fungi or fungus-like microorganisms, including Pythium spp., Phytophthora spp., Fusarium spp., and Rhizoctonia solani, can 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 presents as poor germination. If the disease develops after plant emergence, seedlings that fall over or die are said to have "damping-off." The disease's destructiveness depends on environmental conditions and the level of pathogens in the soil. Cool temperatures, wet soil, compacted soil, high humidity, overcast conditions, and overcrowding are especially favorable to damping-off. Poor ventilation in greenhouses and contaminated planting medium 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.
Cultural control
- 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.
Chemical control
- Seed treatment with one of the following fungicides.
- Apron XL (Group 4) at 0.085 to 0.64 fl oz/100 lb seed plus a dye to control Pythium spp. See label for reentry restrictions.
- Dynasty (Group 11) at 0.10 to 0.38 fl oz/100 lb seed plus a dye. 4-hr reentry.
- Maxim 4FS (Group 12) 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 (Group M3) at 6 oz/100 lb seed (not labeled for Oregon) or 42-S Thiram (Group M3) at 6 fl oz/100 lb seed plus a dye. See label for reentry restrictions.
- Aliette WDG (Group P7; formerly Group 33) 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.
- 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 (Group P5) 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 (Group 4) 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.
Biological control
- Actinovate AG at 3 to 12 oz/A as a soil drench at planting. 4-hr reentry. O
- Actinovate Lawn & Garden at 1/2 to 1 teaspoon/gal water. H O
- Bexfond at 7 to 28 fl oz/A. 4-hr reentry. O
- Cease at 3 to 6 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 1 to 2 quarts/A as a banded soil spray or drench on 4- to 6-week intervals or at 0.5 to 4.5 pints/A on 2- to 4-week intervals. Can be applied the day of harvest. 4-hr reentry. O
- Mycostop at 0.07 oz/lb seed. 4-hr reentry. O
- Rootshield WP at 3 to 8 oz/100 gal water for greenhouse soil drench and field chemigation or at 16 to 32 oz/A as an in-furrow spray. 4-hr reentry. O
- SoilGard at 2 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. 4-hr reentry. 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 2 at 2.6 to 5.2 oz/A on 7- to 14-day intervals can suppress soilborne diseases. 4-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.