DANGEROUS INTERNATIONAL FOREST TREE DISEASES 97 



Ponderosa Pine Needle Cast 



T. W. Childs 



Forest Service, U.S. Department of Agriculture, Portland, Oregon 



Elytroderma deformans (Weir) Darker. A perennial disease of 

 pitch pines in North America. Infected needles are usually stunted, 

 becoming pale near the end of their first summer and red brown the 

 following spring, fading to gray in the late summer and falling in the 

 early winter of their second year. Necrotic lesions form in twig 

 phloem, tips of twigs curl upward, and old infections on trees of fair 

 to good vigor develop into compact, globose witches'-brooms. On 

 year-old needles, inconspicuous tendrils of hyaline conidia appear in 

 the spring; dark, linear hysterothecia become conspicuous during the 

 summer. Hysterothecia are amphigenous, sometimes several mm. long, 

 scattered or in series, and opening by a longitudinal fissure; asci are 

 fusiform and 30-45 X 140-240/a; paraphyses, filiform and 2- or 

 3-septate; ascospores are 1-septate at maturity, cylindric or slightly 

 fusiform, often somewhat curved 6-8 X 90-1 18/x, surrounded by a 

 gelatinous sheath, and discharged in the fall. 



Kequirements for infection by spores are apparently exacting, but 

 heavy waves of infection sometimes occur on trees of all sizes, causing 

 severe local damage. The fungus perennates in twig phloem and buds, 

 invading needle primordia soon after their formation. If most of the 

 twigs on a tree become infected, recurrent annual infection by spores is 

 not necessary for death to occur in 4 or 5 years from defoliation. Less 

 severe infection retards growth and deforms young trees. 



Intercontinental spread is possible through shipment of infected 

 trees. Retention in quarantine is not a sufficient safeguard, since dis- 

 eased twigs occasionally become symptomless for a year or longer and 

 then once again produce fruiting bodies of the fungus on their needles. 



Range: In North America it is common from western Canada south- 

 ward into California and eastward to the Rocky Mountains ; rare 



in eastern Canada and United States. 

 Hosts: Pinaceae — 



Pinus ponderosa Laws. 



P. jeffreyi Grev. & Balf . 



P. contorta Dougl. 



P. edulis Engelm. 



P. banksiana Lamb. 



P. echinata Mill. 

 Literature : 

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



Arboretum 1 : 1-131, illus. 1932. 

 Weir, J. R, Hypoderma deformans, an undescribed needle fungus 



of western yellow pine. Jour. Agr. Res. 6 : 277-288, illus. 1916. 



