Cercospora blight is a serious disease of junipers in the Great Plains. The disease was once considered a variant of Cercospora needle blight which occurs in the Southeastern U.S., Japan and Brazil but has now been separated out. The causal organism of the disease which occurs in the north-central U.S. and southern Canada is Pseudocercospora juniperi (Ellis & Everh.) Sutton & Hodges (syn. Cercospora sequoiae var. juniperi Ellis & Everh.). Several members of the Cupressacea family are hosts of the fungus. Rocky Mountain juniper is the most severely affected host in the Great Plains but Eastern redcedar may also suffer extensive injury on occasion. Foliage on junipers is divided into three categories: (1) juvenile needles found on seedlings, (2) spur needles found on short spur branches and (3) whip foliage found on long shoot growth at the ends of secondary and tertiary branches. Knowledge of the types of foliage is important in understanding disease development. Pseudocercospora juniperi overwinters in infected leaves on the tree. Conidia are formed on stroma and disseminated during periods of warm wet weather from April to October. Spores are dispersed short distances by splashing or wind driven water. Long distance spread is rare. Spores germinate and penetrate host leaves through stomata or directly through the cuticle. Free moisture must be present for spore germination and infection to occur. Initial infection takes place in juvenile needles and previous years' spur needles in the inner crown. Whip foliage appears to be resistant. The period of initial infection in Nebraska is late June and July. The time between infection and symptom development is 2 to 3 weeks. Stroma containing conidia are formed on infected tissue and appear as small, raised, fuzzy gray "spots" on infected foliage. The disease generally spreads to all needles on spur shoots. Cercospora blight can be very severe in older windbreaks. Substantial injury does not occur in nursery stands except on grafted selections, particularly those left in the nursery 5 to 6 years. The disease tends to be more severe in plantings oriented north-south than in those planted with an east-west orientation.
Coziahr, L,V. and Wysong, D.S. 1987. Juniper blight diseases. Cooperative Extension, Institure of Agriculture and Natural Resources, Univ. of Nebraska - Lincoln. NebGuide G87-858.
Hansen, E.M. and Lewis, K.J., eds. 1997. Compendium of conifer diseases. APS Press. St. Paul, MN. 101 pp.
Riffle, J. W., and Peterson, G.W., tech coords. 1986. Diseases of trees in the Great Plains. U.S. For. Serv. Gen. Tech. Rep. RM-129. 149 pp.
Sinclair, W.A., Lyon, H.H., and Johnson, W.T. 1987 Diseases of trees and shrubs. Cornell University Press. Ithaca, NY. 574 pp.
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This page was researched and drafted by: Jane Christensen, Department of Plant Pathology, University of Nebraska-Lincoln
Disease images were provided by: Dr. David Wysong, Department of Plant Pathology, University of Nebraska-Lincoln
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