CONTROL OF LETTUCE DROP BY THE USE OF 
FORMALDEHYDE 1 
By Webster S. Krout 2 
Assistant Research Professor of Botany, Massachusetts Agricultural Experiment Station 
INTRODUCTION 
The growing of head lettuce under gla^s has been developed to a very 
high degree in the Boston market garden district and other parts of 
Massachusetts. It is usually the main greenhouse crop, and not uncom¬ 
monly the market gardener grows 4 to 6 acres under glass. In many of 
these houses the soil has not been changed for 20 years or more. As a 
result it has become so thoroughly infested with Sclerotinia libertiana 
Fckl., the fungus which causes drop, that the loss to the crop is some¬ 
times enormous. 
Investigations on this disease were begun by Stone and Smith (7, p. 3) 3 
of the Massachusetts Agricultural Experiment Station as long ago as 
I ^95- In the course of their work they devised a method of soil steriliza¬ 
tion by the use of steam, and since 1900 this has been in more or less general 
use for the control of drop. The method has some serious disadvan¬ 
tages, however, which led in 1914 to the reopening of the investigation by 
the department of botany of the same station. 
REVIEW OF LITERATURE 
There are few experimental data available dealing specifically with the 
control of 5 . libertiana by the use of formaldehyde. Smith (5) states that 
the mycelium of S. libertiana , growing on pieces of lemon crates, was 
killed by immersing it for 1, 5,* and 10 minute periods in a 5 per cent 
formaldehyde solution. Treating the same fungus with formaldehyde 
as it occurs naturally in lettuce beds, Stevens ( 6 ) and Reddick (8, p. 206) 
report negative results, whereas Clinton’s (4) results were of a positive 
nature. Since the completion of this work Beach ( 2 ) reports slight gains 
with^the use of formaldehyde on out-of-doors lettuce beds. Also, New 
Jersey Agriculture (j) reports similar results with the use of formalde¬ 
hyde on out-of-doors seed beds. 
Although the literature contains conflicting reports on the efficacy of 
formaldehyde used as a soil disinfectant, our own preliminary tests indi¬ 
cated that the material might have considerable value in the control of 
lettuce drop. Consequently the work was concentrated on the use of 
formaldehyde in this connection, and extensive laboratory and green¬ 
house tests have been made. The work has included treatment of large 
commercial greenhouses on a practical basis. 
1 Accepted for publication Jan. 16, 1922. Published with the approval of the director, Massachusetts 
Agricultural Experiment Station. 
* The writer is greatly indebted to Prof. A. Vincent Osmun, head of the Department of Botany of this 
Station for his many helpful suggestions during the progres of this study. 
3 Reference is made by number (italic) to “Literature cited,” p. 654. 
Journal of Agricultural Research, 
Washington, D. C. 
abh 
(64s) 
Vol. XXIII, No. 8 
Feb. 24, 1923 
Key No. Mass.-7 
