UNITED STATES DEPARTMENT OF AGRICULTURE 
S BULLETIN No. 577 vu 
Contribution from the Bureau of Plant Industry 
jt&'^ru WM - A - TAYLOR » Chief 
Washington, D. C. PROFESSIONAL PAPER September 14, 1917 
EXPERIMENTS IN THE CONTROL OF POTATO LEAK. 1 
By Lon A. Hawkins, Plant Physiologist, Plant Physiological and Fermentation 
Investigations, Bureau of Plant Industry. 
CONTENTS. 
The causal organisms 1 
Methods of investigation 2 
Page. 
Results of the experiments 3 
Conclusions 5 
THE CAUSAL ORGANISMS. 
In a paper 2 on a disease of potatoes commonly known as leak, the 
disease was described and the literature on the subject reviewed. It 
was shown that the tuber rot typical of this disease could be caused 
by Rliizopus nigricans Ehrenb., as Orton 3 found, but that the causal 
organism was more frequently Pythium debaryanum Hesse. The 
fungus obtains entrance through breaks in the skin of the potatoes, 
and infection under field conditions usually takes place by some in- 
fected soil getting into wounds made in harvesting. Preliminary 
experiments in 1915 indicated that the disease could be controlled 
by carefully sorting out all wounded tubers. As the disease is of 
considerable economic importance in the delta region of San Joaquin 
County, CaL, it was considered advisable to continue these experi- 
ments. This bulletin deals with further experiments in the control 
of the disease, together with some additional work on the causal 
organism and its occurrence in the delta soils. 
1 The work described in this bulletin was carried out as a part of the potato-disease project of the Office 
of Cotton and Truck Disease Investigations. The writer wishes to acknowledge his indebtedness to Mr. 
Carson C Cook, of Stockton, Cal., for his hearty cooperation in this work. 
2 Hawkins, L. A. The disease of potatoes known as "leak." In Jour. Agr. Research, v. 6, no. 17, pp. 
627-640, 1 fig., pi. 90. 1916. 
8 Orton, W. A. Potato diseases in San Joaquin county, California. U. S. Dept. Agr., Bur. Plant Indus. 
Circ. 23, 14 p. 1909. 
Decay of potatoes due to Rhizopus nigricans. (Abstract.) In Science, n. s., v. 29, no. 753, 
p. 916. 1909. 
1903°— Bull. 577—17 
