Cause The fungi or fungus-like microorganisms, Pythium spp., Fusarium spp., and Rhizoctonia solani, attack young seedlings of many vegetables, including members of the genus Brassica. These soilborne microorganisms can persist indefinitely in soil or plant debris. If seedlings are affected before emergence, it appears as poor germination. If the decay is after emergence, seedlings that fall over or die are said to "damp-off." The destructiveness of the disease depends on the amount of pathogen in the soil and on environmental conditions. Cool, cloudy weather, high humidity, wet soils, compacted soil, and overcrowding especially favor development of damping-off.
Symptoms Damping-off kills seedlings before or soon after they emerge. Beneath the soil a general rot is observed. Seedlings that emerge develop a lesion near where the tender stem contacts the soil surface, and the seedling collapses. In some cases, the seedling may continue to grow even though the lesion girdles the stem. The lesion is quite sunken, and the stem resembles a wire, hence the name wirestem. The girdled seedling eventually dies.
- In the greenhouse or seedbed, pasteurize the soil with heat. Use good sanitation in greenhouses.
- Locate seedbeds on well-drained soil, and avoid excessive irrigation.
- Space rows and/or seedlings in the seedbed to maximize air movement.
- Carefully examine seedlings when transplanting; discard any with signs of wirestem.
- 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.
- Crop rotation with cereals may reduce pathogen populations in the soil.
- Remove or encourage decomposition of plant debris.
- Seed treatment may help combat these diseases.
- Allegiance-FL (Group 4) at 0.75 fl oz/100 lb seed plus a dye. Controls only Pythium spp. See label for reentry restrictions.
- Apron XL (Group 4) at 0.085 to 0.64 fl oz/100 lb seed plus a dye, can be used where Pythium spp. are a problem. See label for reentry restrictions.
- Captan 4F at 2.2 fl oz/100 lb seed plus a dye.
- Coronet fungicide seed treatment at 5.1 to 6.2 fl oz/100 lb seed (commercial seed treaters only) plus a dye.
- Dynasty (Group 11) at 0.1 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. For control of pathogenic Fusarium and Rhizoctonia spp. See label for reentry restrictions.
- 42-S Thiram at 8 fl oz/100 lb seed plus a dye. See label for reentry restrictions.
- Apply fungicide to soil or base of transplants.
- MetaStar 2E AG at 1 to 2 pints/A at planting treatment. For control of Pythium spp. 48-hr reentry.
- Quadris Flowable at 0.4 to 0.8 fl oz/1000 row feet applied in a 7-inch or less band either in-furrow at planting or as a directed spray at cultivation. 4-hr reentry.
- Moncut (Group 7) at 1.1 lb/A at planting. Preharvest interval is 45 days. 12-hr reentry.
- Uniform at 0.34 fl oz/1000 row applied as an in-furrow application at planting for Chinese cabbage only.
- Actinovate AG at 3 to 12 oz/A as a soil drench at planting. 4-hr reentry. O
- Actinovate Lawn & Garden at 0.5 to 1 teaspoon/gal water. H O
- Bio-Tam 2.0 at 2.5 to 5 lb/A as a broadcast at sowing. See label for different methods and rates of application. 4-hr reentry. 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/half lb seed. 4-hr reentry. O
- Prestop as a soil drench or incorporation into growing medium. 4-hr reentry. 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
- 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