By M. Putnam
Cause Soilborne fungal and fungus-like microorganisms such as Rhizoctonia solani, Pythium sp., and Phytophthora sp. They are widespread in soil and can be very destructive under cool, moist conditions.
Symptoms Damping-off kills seedlings before or soon after they emerge from the soil. Beneath the soil a general rot is on affected seed. Seedlings that emerge develop a lesion on the stem near the soil surface. The seedling usually collapses; in some cases it continues to grow even though the lesion girdles the stem, but it grows poorly and eventually collapses. Main roots of affected seedlings are discolored, may develop forks, and lack secondary roots.
Cultural control
- Avoid establishing beds in low areas that collect water.
- Plant in beds raised at least 6 inches to improve drainage.
- Do not plant ginseng immediately after alfalfa.
- Avoid excessive seeding rates. A good goal is 120 plants/sq yard; for example, use 90 to 100 lb seed/A if germination rate is 70%.
- Avoid excessive manure or fertilizer applications. If using a green manure, allow 3 weeks after turning in the green manure crop before planting.
- Delay, when possible, shading the gardens in the spring until soil warms up, to encourage more rapid seedling emergence.
- Avoid excessive fertilization or application of manures, which encourage lush growth that is more susceptible to disease.
Chemical control
- Apron XL at 0.085 to 0.64 fl oz/100 lb seed. Will control Pythium, but not Rhizoctonia. Group 4 fungicide.
- Maxim 4 FS at 0.08 to 0.16 fl oz/100 lb seed. Effective against Rhizoctonia but not Pythium. Group 12 fungicide.
- MetaStar 2E at 1.5 quart/A as a onetime drench in the spring against Pythium and Phytophthora. Group 4 fungicide. 48-hr reentry.
- Omega 500 F at 1 pint/A beginning at transplant for Rhizoctonia. Do not use within 30 days of harvest. Group 29 fungicide. 12-hr reentry.
- Orondis Gold at 28 to 55 fl oz/A as a drench, soil-directed spray or through irrigation water. Do not use within 14 days of harvest. Group 4 + 49 fungicide. 48-hr reentry.
- Quadris Flowable at 0.4 to 0.8 fl oz/1,000 row feet applied in a 7 inch or less band either in-furrow at planting or as a directed spray at cultivation. Suggested for Rhizoctonia. Group 11 fungicide. 4-hr reentry.
- Ridomil Gold GR at 10 to 15 lb/A can be used against Pythium and Phytophthora but is ineffective against Rhizoctonia. Do not use within 9 days of harvest. Group 4 fungicide. 48-hr reentry.
- Ph-D WDG at 6.2 oz/A may be useful for Rhizoctonia. Group 19 fungicide. 4-hr reentry.
Biological control Use in conjunction with other control tactics such as thorough sanitation.
- SoilGard (Gliocladium virens strain GL-21) at 5 lb/A soil incorporated 4 days prior to planting. No reentry interval required. O
- Stargus at 6 to 8 fl oz per 1,000 ft row as an in-furrow treatment, 3 to 4 quarts/A as a soil drench on 10- to 14-day intervals, or 3 to 4 quarts/A as a chemigation drip treatment on 14- to 21-day intervals. Preharvest interval is 0 days. 4-hr reentry. O
Reference Reeleder, R.D. and Brammall, R.A. 1994. Pathogenicity of Pythium species, Cylindrocarpon destructans, and Rhizoctonia solani to ginseng seedlings in Ontario. Canadian Journal of Plant Pathology 16:311-316.