UNITED STATES DEPARTMENT OF AGRICULTURE 
BULLETIN No. 799 
Contribution from the Bureau of Plant Industry 
WM. A. TAYLOR, Chief 
Washington, D. C. PROFESSIONAL PAPER June 19, 1919 
THE LEAF-SPOT DISEASES OF ALFALFA AND RED 
CLOVER CAUSED BY THE FUNGI PSEUDO- 
PEZIZA MEDICAGINIS AND PSUEDOPEZIZA TRI- 
FOLII, RESPECTIVELY. 
By FrRepD REUEL JonEsS. Pathologist, 
Cotton, Truck, and Forage Crop Disease Investigations. 
——_ —--—_—_—_—_ 
CONTENTS. 
Page. 3 Page. 
Scope of the investigation....-.-..-..-------- 1 | The fungi—Continued. 
Dif TISEISES. socosscesesnassoonedesseescusase 2 Reported conidial stages of these fungi... 9 
Economicimportance........-.--------- 2 Physiology of the fungi.................. 11 
Description of the disease on alfalfa. ...-. 3 Pathogenicity of the fungi..............- 19 
Description of the disease on red clover. 4 | Life history of the causal organism in relation 
TEITS i (TRIES S85 saoseoSnosecsscossabeoe- 5 tothe host plants..............--..---- 27 
CHG NIE SececdeeaS anc OnE EE nse bcoeaBdEae 5 American studies bearing on life history. 27 
Synonomy of Pseudopeziza trifolii-...... 5 Method of overwintering........-.-.----- 28 
Synonomy of Pseudopeziza medicaginis. 6 Method of distribution Biralnier sie <lativopela ates 30 
Comparative morphology of the fungi... - (@ || bbw 6 oséscesscSbobbdoodcossosbocooaKS- 35 
Morphological characters in culture. .-..- 8 | Literature cited....--..-..-.....-.--.-2---- 36 
SCOPE OF THE INVESTIGATION. 
Among the diseases of the foliage of the alfalfa plant, the one 
which is most widely known and is reported to cause the greatest loss 
is the leaf-spot caused by the fungus Pseudopeziza medicaginis. The 
disease is commonly called the alfalfa leaf-spot. This name is not 
distinctive, and its continued use is open to the objection that it 
promotes the present tendency to apply it inclusively to all the sev- 
eral leaf diseases that may be present with the true leaf-spot. How- 
ever, the usage is so prevalent that it appears likely to persist. 
Although the importance of the disease has caused it to. be men- 
tioned widely and frequently, little careful study has been devoted 
to it. A great number of scattered and conflicting observations have 
left the life cycle of the fungus causing the disease in doubt; the 
89950°—19——-1 
