48 U.S. DEPT. OF AGRICULTURE MISC. PUB. 939 



Spermogonia, 83-165 X 74— 143/x, are formed on both green and fallen 

 needles throughout autumn and winter. The mature spermogonia are 

 filled with a great number of hyaline, rod-shaped spermatia, 

 3-5 X 0.5-1/a in size. 



Perithecia are produced on the fallen needles in contact with the 

 soil. Early in March structures that are interpreted to be perithecial 

 initials are observed. Perithecia develop either singly or in groups, 

 at first embedded within the host tissue, but later becoming erumpent. 

 Ascospores mature in May to July. Mature perithecia are amphige- 

 nous, single or in groups, partially erumpent, globose, 88-157 X 84- 

 14%. Asci are clavate-cylindrical, 49-99 X 7-12/x, contain 8 ascospores. 

 Paraphyses are absent. Ascospores are hyaline, unequally two-celled, 

 constricted at septum, 11-18 X 3-5/x. 



This is one of the most important diseases of larch forests. The 

 characteristic symptom of this disease is a browning of the needles over 

 all or part of the crown. This browning is most conspicuous in sum- 

 mer and autumn and gives the impression that the tree is dying. Later 

 the diseased needles drop off, leaving the trees with all or portions of 

 their crowns thin and the remaining needles confined to tufts at the end 

 of the branches. Repeated serious defoliations bring about a consid- 

 erable decrease in growth increment. 



The source of infection is diseased needles, and intercontinental 

 spread may be possible by seedlings and stocks bearing needles. 



Range : Northern and central parts of Japan. 



Hosts : Pinaceae (species listed in order of susceptibility) — 



Larix decidua (Planted in Japan) 



L. gmelini var. olgenis (Planted in Japan) 



L. gmelini var. japonica 



L.leptolepis (L.kaempheri) 



Literature : Ito, K. ; Sato K. ; and Ota, N. Studies on the needle cast 

 of Japanese larch — I. Life history of the causal fungus, Mycos- 

 phaerella laricileptolepis sp. nov. Bui. Govt. Forest Expt. Sta. 

 96 :69-88. 1957. 



Shoot Blight of Larch 



Physalospora laricina Sawada. Stems of seedlings and shoots of 

 young trees are attacked. Lesions are more or less sunken and fre- 

 quently exude resin. Diseased stems and twigs are girdled, killed, 

 and then defoliated. Many dieback twigs are seen in the crowns of 

 heavily diseased trees. Perithecia are produced under the epidermal 

 tissues of killed twigs and stems. 



Perithecia are black, globose, erumpent, 368** in diameter. Asci 

 are clavate, rounded at apical portion, hyaline, 114—135 X 22-26/z. 

 Paraphyses are Sfx in diameter, rarely branched. Ascospores are 

 elliptic, smooth, 24—27 X 13/x. Imperfect stage, Macrophoma, is 

 found on both twigs and leaves. 



This is currently the most serious disease of larch forests in Japan. 

 Though trees of all ages are susceptible, young trees are very heavily 

 attacked. Infected trees are malformed and growth is greatly reduced. 



International spread may be possible by infected trees or scions. 

 Importation of living plant material other than pollen or seed should 

 be forbidden except for experimental use following rigorous insper- 



