Forest Pests: Insects, Diseases & Other Damage Agents

Ash Dieback - Various causal agents

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. - White ash and green ash trees in forests, shelterbelts, and landscape plantings of the Northeastern and North Central United States are affected substantially by this malady.

Identifying the Disease. - Symptoms of abnormal growth are similar to those described for ash yellows. Epicormic sprouts and witches' brooms, indicators of MLO infection, have been associated with ash dieback. Stem and branch cankers caused by various fungi often lead to progressive crown dieback.

Identifying the Causal Agents. - Decline of ashes in the absence of MLO infection is usually due to multiple biotic and abiotic agents. Drought may be the primary cause of dieback in many areas. A list of other possible causal agents includes at least three viruses, two fungal pathogens (Cytospora pruinosa and Fusicoccum spp.), freeze damage, and air pollutants.

Biology. - The initial development of ash dieback frequently involves drought stress, which may be aggravated by freeze damage, or the presence of one or more opportunistic fungal pathogens or viruses. Stress induced by other agents may be worsened by MLO infections in white or green ash.

Control. - In forests, sites should be carefully selected and species composition managed to avoid having mature ashes on droughty sites. Tree stress may be reduced in landscape plantings by fertilization and irrigation during dry weather.

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