A SERIOUS LETTUCE DISEASE. 
93 
and rotting of the outer leaves, followed usually by dropping and rot¬ 
ting of the rest of the plant, this disease has come to he called “the 
drop,” by lettuce growers in many sections of the country. These 
symptoms may be produced by several different causes. 4 
“The drop” is therefore not one single definite disease. It is rather 
a condition or a symptom just as lameness of horses is a condition or 
a symptom, not a disease. Lameness may be due to spavin, which is 
one disease, or to tuberculosis, which is another, etc. So the drop may 
be due to Sclerotinia, to Pythium, to Botrytis, etc., each of these caus¬ 
ing a separate disease and each requiring different treatment and 
prophylaxis according to the nature of its cause. 
The first definite knowledge of the existence of lettuce Sclerotiniose 
is contained in a communication by Smith in 1900. 4 
The disease is there first clearly and accurately characterized and 
attributed to its causal fungus, Sclerotinia libertiana Fckl. While 
1900 is thus the earliest date of accurate knowledge concerning this 
disease, it was in all probability seriously injurious long before that 
time, and many serious lettuce troubles reported from different parts 
of the United States, and attributed to other causes, were doubtless 
really due to Sclerotinia. Sclerotiniose frequently occurs in conjunc¬ 
tion with other lettuce diseases and in many instances inroads upon 
the lettuce beds attributed to Botrytis, Rhizoctonia, Bacteria, or other 
causes, were probably due in part, even in main, to sclerotiniose, often 
doubtless complicated by one or more of these other diseases. Among 
such early, hut somewhat uncertain cases are the following: 
Prof. G. E. Stone, of Massachusetts, says in a letter to the senior 
author (April, 1908), “I think we have evidence to show that the 
disease has been here a number of years, and that it is not a native 
in this region. It was doing considerable damage in the lettuce houses 
in the 90’s—I think the fungus is not indigenous as it does not occur 
in some of our greenhouses in this State. I know many greenhouses 
which became infected with the drop through the introduction of 
plants from the Boston market-garden district. When I first studied 
the disease I had to introduce it into my greenhouse, and I knew of a 
number of houses at that time which never had it. 
“I do not believe the disease troubled the very early lettuce growers, 
and I imagine it was not severe in the 90’s. I do not believe the men 
who grew lettuce for 40 or 50 years had' much trouble in growing it 
under sash or even in their old greenhouses. My predecessor in the 
station, Prof. Humphrey, I think probably had the same trouble under 
observation when he was here in 1888 or 1889, and probably some of 
the other observers who described the bacterial disease of lettuce, had 
the drop. I have always considered that Sclerotinia and eel worms 
were both introduced organisms, and were not indigenous to our State. 
What I have said in regard to the sclerotium being absent from some 
houses for many years, also applies to eel worms, since there are 
many houses which have never been troubled with these. I look upon 
many of these diseases as simply the result of extensive commercial 
relations with foreign countries.” 
