Forest Pests: Insects, Diseases & Other Damage Agents

Damping-Off - Cylindrocladium spp., Fusarium spp., Phytophthora spp., Pythium spp., Rhizoctonia spp.

Solomon, J.D.; Leininger, T.D.; Wilson, A.D.; Anderson, R.L.; Thompson, L.C.; McCracken, F.I. 1993. Ash pests: A guide to major insects, diseases, air pollution injury and chemical injury. Gen. Tech. Rep. SO-96. New Orleans, LA: U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station. 45 p.

Importance. - Damping-off is the most important and widespread disease of ash seedlings in tree nurseries. The disease is most prevalent in cool, low-lying areas where standing water persists, in acidic soils, and under any conditions where seedling growth is poor. Seedling density may be reduced up to 25 percent or more when poor cultural practices are used.

Identifying the Disease. - Damping-off may prevent the emergence of seedlings from the soil as the seeds or hypocotyls are attacked. Seedlings attacked after emergence fall over because the hypocotyls are rotted at or below the soil line. Both types of damping-off result in reduced seedling survival causing nonuniform seedling sizes and densities.

Identifying the Fungi. - Many fungi prevalent in soils can cause damping-off. Fursarium spp., Pythium spp., and Phytophthora spp. are most active in cool, wet soils, whereas Cylindrocladium spp. and Rhizoctonia spp. are more common in warm, wet soils.

Biology. - The soil-borne fungi that cause damping-off of seedlings are able to survive in the soil in the absence of a host. All produce resistant spores or sclerotia that survive in the soil until root exudates stimulate their germination or growth, leading to the infection of seeds or seedlings.

Control. - Damping-off can be controlled with cultural practices. Seeds should be planted on well-drained sites or in raised beds at soil temperatures above 15 degrees C, avoiding dense stands. Nitrogen fertilizers should not be applied until seedlings are 6 weeks old. Soil acidity should be maintained at pH 6.0 or slightly above. Soil fumigation or seed treatment with fungicides is sometimes necessary for adequate control.

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