DANGEROUS INTERNATIONAL FOREST TREE DISEASES 99 



Hosts: Pinaceae — 



Pinus clausa (Engelm.) Vasey. Florida. 



P. echinata Mill. Pennsylvania, Virginia to Florida, Alabama, 



Louisiana, West Virginia, Tennessee, Missouri. 

 P. elliottii Engelm. var. elliottii. South Carolina to Florida, 



Mississippi. 

 P. nigra Arnold. New York, Pennsylvania. 

 P. nigra var. austriaca Aschers. & Graebn. Rhode Island, New 



Jersey. 

 P. pungens Lamb. North Carolina. 

 P. resinosa Ait. New York ( ? ) , Michigan ( ? ) . 

 P. rigida Mill. Maine to South Carolina, Mississippi, Ohio, 



Tennessee. 

 P. serotina Michx. North Carolina to Florida. 

 P. taeda L. Virginia to Florida, Alabama, Tennessee. 

 P. virginiana Mill. Pennsylvania to Florida, Tennessee. 

 Literature : 

 Boyce, J. S., Jr. Hypoderma needle blight of southern pines. 



Jour. Forestry 52 : 496-498. 1954. 

 Darker, G. D. The Hypodermataceae of conifers. Contrib. Arnold 



Arboretum 1 : 1-131. 1932. 

 Hedgcock, G. G. Notes on the distribution of some fungi associ- 

 ated with diseases of conifers. Plant Dis. Rptr. 16 : 28-42. 1932. 

 Morris, C. L. Chemical control of Hypoderma lethale on pitch pine. 

 Plant Dis. Rptr. 37 : 368-370. 1953. 



Hypoxylon Canker of Aspen 



J. R. Hansbrough 



Forest Service, U.S. Department of Agriculture, Washington, D.C. 



Hypoxylon pruinatum (Klotsche) Cooke is a perennial, girdling, 

 stem and branch canker of Populus in North America. The first 

 symptom on aspen bark is small, yellowish-orange, slightly depressed 

 area with irregular margin. Later, the outer bark is raised in blister- 

 like patches, sloughs off, and exposes the blackened, crumbling inner 

 bark. Cutting into the bark of young cankers or near the margin of 

 older cankers shows the laminated, mottled, black and yellowish-white 

 cortex. Removal of all the bark exposes the typical white mycelial 

 fans in the cambial zone. Advancing canker margin is irregular, 

 yellowish orange, sometimes marked by a brownish varnishlike sap 

 flow. Invasion of new tissue is too rapid to permit callus formation. 



Conidia are produced under blisters at the end of the first or during 

 the second year after infection, accompanied by formation of hyphal 

 pegs or pillarlike structures that push the outer periderm from the 

 underlying cortical tissue. Conidia are one-celled, oblong to ovoid, 

 hyaline (brownish in mass), 4-7 X 1-2/x. In the third year perithecia 

 are produced in erumpent, flattened, hard, black stromata, thinly cov- 

 ered with a white pruinose layer through which protrude the 'black 

 ostioles of the sunken perithecia. Asci are cylindrical, with eight one- 

 celled, brown, oblong to elliptical ascospores, 22-30 X 8-13/x. 



This is the most serious disease of the aspens in North America. 

 Trees of all ages are susceptible. Infection is by windbome spores 



