Feb. 34,1923 
Control of Lettuce Drop with Formaldehyde 
647 
required to kill small sclerotia was 15 minutes (Table I, treatments 1 
and 3), while all large sclerotia were killed in 20 minutes (Table I, treat¬ 
ments 2 and 4). In a 1-100 solution the maximum time required to kill 
small sclerotia was 15 minutes (Table III; treatments 1, 3, and 8), 
whereas all large sclerotia were killed in 30 minutes (Table III, treatments 
2, 4, 7, and 9). In a 1-200 solution the maximum time required to kill 
small sclerotia was 75 minutes (Table I, treatment 5), while all large 
sclerotia were killed in 90 minutes (Table I, treatments 6 and 7). In 
each concentration the small sclerotia were killed in less time than the 
large. Also, results show (fig. 1) that the longest time required to kill 
sclerotia of any size is inversely proportional to the strength of the solu¬ 
tion. Furthermore, it should be noted (fig. 1) that a 1-100 formaldehyde 
solution is almost as effective as a 1-50 solution but that a 1-200 solution 
is much less effective than the stronger solutions. 
Sclerotia of lots 1, 2, 3, 4, and 7 (Table I) were taken from plants that 
showed drop symptoms 10 days before the sclerotia were removed; lots 
5 and 6 were taken 12 days after the first symptoms of drop were noticed 
on the plants. 
Tabi,® I .—Effect of formaldehyde on sclerotia 
TREATMENT OF MYCELIUM 
The white aerial mycelium of pure cultures or of diseased lettuce 
plants was thoroughly moistened by transferring for a few minutes to 
sterile distilled water. It was then removed and treated with the 
desired strength of formaldehyde solution for different periods of time. 
At the end of the exposure the mycelium was removed aseptically, 
washed in sterile distilled water, and transferred to nutrient agar plates. 
The results are recorded in Table II. 
Mycelium from pure culture was killed in 5 to 10 minutes in a 1-50 
or a 1-100 formaldehyde solution, and in 15 to 20 minutes in a 1- 200 
solution. Mycelium from diseased lettuce plants was killed in 10 to 15 
minutes in a 1-50 or a 1-100 formaldehyde solution (Table II). The 
mycelium of pure cultures was killed in less time than mycelium from 
diseased lettuce plants. 
The curve of figure 2 shows that the 1-50 and the 1-100 formaldehyde 
solutions are equally efficient in killing the mycelium of 5 . libertiana 
and that the 1-200 solution is decidedly less effective than the other two. 
It is interesting to note that this held true in most cases throughout 
these experiments. 
