Damping-off in Flower and Vegetable Seedlings
Ornamental Disease Note No. 14
Ronald K. Jones, Plant Pathologist (retired)
Charles W. Averre, Plant Pathologist (retired)

Cause

Damping-off is primarily caused by fungi present in the growing medium. The fungi include species of Rhizoctonia, Pythium, Fusarium, Phytophthora, Sclerotinia, Sclerotium, Botrytis, and others. Germinating seed and seedlings, especially weak ones, are vulnerable to attack by these fungi during periods of unfavorable growing conditions. Species of Pythium, Sclerotinia, and Phytophthora are more likely to cause damping-off in cool, wet soils; whereas species of Rhizoctonia, Fusarium and Sclerotium rolfsii may cause damping-off under warmer and drier conditions.

True damping-off may be confused with plant injury caused by excessive fertilization, high soluble salts, drowning in wet soil, desiccation in dry soil, and death of seedlings from excessive heat, cold, fuel fumes, or chemical injury. This type injury often damages the leaves and upper stem before the roots are affected.

Symptoms

Typical symptoms of damping-off are rotting stems at or near the soil line and root decay (post-emerging damping off). Affected areas in the seed bed are usually a foot or more in diameter with shriveled brown, collapsed or stunted seedlings. Moldy fungal growth may be seen on affected plants at the soil line. Germinating seed can also be attached by these fungi before they emerge from the soil (pre-emerging damping off), resulting in poor stands. Rhizoctonia, Fusarium, Sclerotinia, and Sclerotium generally caused post emergence damping-off by killing the seedling at the soil line. Pythium attacks below the soil line, often at root tips.

Control

The best control of damping-off is to avoid it altogether. Once damping-off has started in a plant bed or seedling flat, it may be difficult to control. the general methods employed to prevent damping-off consist of :
1) proper soil preparation and management to provide for good soil drainage, structure, aeration, water-holding capacity and plant nutrition by including proper amounts of fertilizer and lime according to the soil test report,
2) proper soil treatment with heat or chemicals to reduce the level of fungi that cause damping-off (see Plant Pathology Information Note No. 170),
3) the use of fungicide-treated seed with high germination (see Agricultural Chemicals Manual; specify treated seed before purchasing),
4) proper seeding rates to avoid thick plant stands, poor air movement and low light intensity,
5) proper planting depth and soil temperature to assure rapid seeding emergence, growth, and
6) strict sanitation to avoid reinfesting treated soil with these fungi. Many outbreaks of damping-off in North Carolina can be attributed to poor sanitation practices after treating the soil. For bedding plant operations, it may be more practical to buy a sterilized soilless mix and eliminate steps 1 and 2 above.

Once damping-off has started in a bed or flat, its spread may be reduced by providing drier conditions for better seedling growth. This can be done by increasing greenhouse temperature, increasing air circulation and ventilation, reducing the frequency of watering, providing better water drainage by ditching inside and outside the plant bed structure or greenhouse, and by increasing the amount of light by removing dirty covers, overhanging branches, removing shading materials, etc.

If the above preventive control measures fail, several fungicides are available that may be effective if applied as a drench or heavy spray as soon as the first symptoms of damping-off are observed. Growing conditions should be improved and flats or areas of bed with damping-off should be carefully removed from the growing area. Rapid identification of the causal fungus should be obtained so that proper chemicals can be applied (see county agent for diagnosis). Several applications of the fungicide may be necessary, If the specific fungus causing damping-off is not known, one broad spectrum fungicide (captan or ferbam), two specific fungicides (benomyl plus, etridiazole or metalaxyl) or a prepared combination of fungicides (etridiazole + thiophanate methyl) should be used. Check the current North Carolina Agricultural Chemicals Manual and the label carefully to be sure of the proper fungicide and rate to be used on a particular crop.

Some fungicides used to control damping-off are listed below along with general rates (follow specific crop limitations and rates on the manufacturer's label):

All of these fungicides can cause some stunting and yellowing of young seedlings. Do not use fungicides unless damping-off becomes or has been a problem. Wait as long as possible before using a fungicide as younger seedlings are more susceptible to fungicide injury than older seedlings.

Other Links

Plant Disease Information Notes Home Page
North Carolina Insect Notes
North Carolina Agricultural Chemicals Manual
CALS Home Page
NCCES Home Page
NCARS Home Page

For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service

Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical. For assistance, contact your county North Carolina Cooperative Extension Service agent. 10/90/1000

Reformatted Dec. 2000 by A.V. Lemay