A SERIOUS LETTUCE DISEASE. 
139 
PART II.* 
A Practical Test of a Curative Treatment. 
The conclusions as recorded above, deduced from several years of 
laboratory and field study of this disease, especially those conclusions 
which point to the sclerotia as the only means of hibernation, began 
to force themselves upon the mind of the senior author some years ago. 
Those conclusions seemed to be so unavoidable and their logical 
effect upon horticultural practice so fundamental and so significant 
that it was deemed imperative to put the question to a crucial test. 
If the theory as enunciated be true, all that is necessary in order to 
rid a Sclerotinia-infected lettuce bed of its pest is to prevent the 
formation of new sclerotia in it for a period of two or perhaps three 
years. 
To make such a test the first essential was a bed thoroughly and| 
unquestionably infected and so located and managed that it would not 
be subject to aerial or other extraneous infection. 
The experimental lettuce beds of the Experiment Station located on 
the farm at West Raleigh are reasonably well isolated from any other 
infected beds which might furnish air-borne ascospores to bring about 
reinfection. Precaution could easily be taken to prevent access of 
sclerotia through manure or other sources. The beds are two in num¬ 
ber, each 208 feet by 9 1-2 feet in size, 30 inches high on the north 
side, 8 inches on the south side, and are covered in the usual way by 
canvas supplemented when need be by burlap mats. They accommo¬ 
date eight rows of plants, 77 plants to the row, with a total capacity, 
therefore, of 1,232 plants. The beds were to some extent infected 
owing to the nature of the experimental work that had been conducted 
in them. This infection was not, however, considered sufficient to 
make the test crucial. 
The first step, therefore, was to thoroughly infect the beds and to 
demonstrate that they were so infected and to secure a record of the 
degree of infection. This was accomplished in the spring of 1908 by 
inoculating several rows or about 67 plants of the then large nearly 
mature marketable lettuce with Sclerotinia mycelium. Within a few 
days, April 18, the plants so inoculated all collapsed and followed the 
usual course of the disease. These plants and considerable other let¬ 
tuce refuse as well were allowed to remain on the ground and since 
the plants were large the number of sclerotia that remained on the 
soil was very great. Thorough infection seemed sure. The lettuce 
was followed by cucumbers and in the autumn of 1908, October, the 
crop was put in in the usual commercial way and the record of disease 
for that year presented in Table XVIII and in Diagram I (Fig. 31), 
shows clearly that a full and thorough infection had been produced. 
The plants, it will be seen, began to die of sclerotiniose in December 
and in January they were dying rapidly. The last record of disease 
♦Printed in part in an earlier Bulletin. (26.) 
