Feb. 24,1923 
Control of Lettuce Drop with Formaldehyde 
653 
| conducted along these lines, both in experimental and commercial 
greenhouses. 
In eight successive lettuce crops grown in the experimental green¬ 
houses at Amherst, the treated plots averaged 2 per cent drop, whereas 
the untreated plots averaged over 50 per cent drop (PI. 1). Several 
large commercial houses were treated with results equally good. 
In the course of the work in was shown that the treatment in all 
commercial houses should begin in the lettuce seed bed and that trans¬ 
planting and permanent beds also must be treated. In all of the green¬ 
house experiments the soil was drenched with a 1-100 formaldehyde 
solution applied at the rate of 1 gallon to the square foot of soil surface. 
No covering was used over the soil after treatment, as it was found to be 
impractical on a large scale and the results showed that it added nothing 
to the efficiency of the treatment. If at any time sterilization is not 
complete or a house has only a few scattered cases of drop the location 
of the dropped plants can be marked with pot markers as the disease 
appears and the roots and tops removed. After the crop is harvested 
the spots where the diseased plants grew can be drenched with a 1-100 
formaldehyde solution. 
Lettuce plants 6 weeks old from seed may be set safely 8 days after 
the application of a 1-100 formaldehyde solution to the soil providing the 
soil is stirred 5 or 6 days after the treatment. But where only a few 
scattered spots are treated plants may be set as soon as the soil can 
be worked. 
EFFECT OF FORMALDEHYDE ON SUBSEQUENT PLANT GROWTH 
During the progress of this study it was manifest from a comparison 
of weights of lettuce plants of the treated and untreated plots that 
formaldehyde increased plant growth. 
For example, 226 mature lettuce plants of a treated area in a commer¬ 
cial greenhouse weighed 164 pounds, while the same number of plants 
taken from an adjacent untreated plot weighed 132 pounds, which 
represents a gain of 23.6 per cent in favor of the plants grown on the 
treated soil. Clinton (4) also has noticed similar results on lettuce. 
Buddin (5) observed in his pot experiments with tomatoes that the crop 
was earlier and of greater bulk in the pots which had been treated with 
formaldehyde. That formaldehyde does increase plant growth must be 
accepted, but the exact reason for it has never been satisfactorily ex¬ 
plained. 
SUMMARY AND CONCLUSIONS 
The maximum time required to kill small sclerotia with 1-50 formalde¬ 
hyde solution in vitro was 15 minutes, and for large sclerotia 20 minutes. 
With 1-100 formaldehyde, small sclerotia, 15 minutes; large sclerotia, 
30 minutes. With 1-200 formaldehyde, small sclerotia 75 minutes; 
large sclerotia, 90 minutes. 
The maximum time required to kill both sizes of sclerotia is inversely 
proportional to the concentration of the formaldehyde solution. 
In a 1-50 or a 1-100 formaldehyde solution in vitro, mycelium from 
pure cultures was killed in 5 to 10 minutes; in a 1-200 solution in 15 to 
20 minutes. 
