JOURNAL OF AGRIdlORAL RESEARCH 



Vol. XIII Washington, D. C, April 29, 1918 No. 5 



ANTHRACNOSE OF LETTUCE CAUSED BY MARSSONINA' 



PA.NATTONIANA 



By E. W. Brandes/ 

 Scientific Assistant in Plant Pathology, Porto Rico Agricultural Experiment Station 



INTRODUCTION 



Lettuce {Lachica saliva) is not an easy crop to grow successfully, be- 

 cause of the peculiarities of the plant, its quick response to unfavorable 

 conditions, and its susceptibility to disease. Any disfigurement of the 

 leaves renders it unmarketable. In this regard it is rather unique, for 

 most other food plants may be attacked in some part by insects or 

 fungi, and still may not be a total loss. 



The disease considered in this paper does its chief damage to green- 

 house lettuce. The methods of culture under glass are very important 

 factors in determining the extent of damage from this disease. In gen- 

 eral, several crops are grown during the winter season. Seeds are sown 

 very thickly in beds, usually in raised benches in a greenhouse devoted 

 to the production of seedlings. After one or more transplantings the 

 small plants, 3 or 4 inches tall, are set out with 6-inch spacings in beds 

 in the main greenhouse. The soil is heavily enriched with manure or 

 other fertilizer. The watering is done either with hose or, in the better 

 greenhouses, with an overhead sprinkling system. The temperature 

 is kept about 55° F. ; and with the best growers ventilation is main- 

 tained practically all of the time, excepting, of course, the extremely 

 cold nights. 



Seed beds are planted so that a succession of crops can be raised. 

 Although some head lettuce is grown, by far the bulk of the crop is of the 

 leaf-lettuce type. The crop is harvested when the plants weigh from 3 

 to 6 ounces, the state of the market and the maturity of the lettuce 

 being governing factors. The bunches are trimmed as harvested, the 

 debris being turned under as a general rule. 



Naturally with such intensive methods as the heavy investment in 

 glass and equipment demands, many parasitic diseases become im- 



1 This work was done at the suggestion of and along lines outlined by Dr. G. H. Coons, of the Michigan 

 Agricultural College, and I am indebted to him for help in the preparation of the manuscript. I also wish 

 to thank Dr. E. A. Eessey, Professor of Botany in the Michigan Agricultural College, for kindly assistance 

 and encouragement during the course of the work. 



Journal of Agricultural Research, Vol. XIII, No. S 



Washington, D. C. Apr. 29, 1918 



ng 261 Key No. B-14 



