2 BULLETIN 601, IT. S. DEPARTMENT OF AGRICULTURE. 
increase from year to year that the crops can not be grown suc- 
cessfully. Oftentimes the problems that have confronted the lettuce 
and celery growers during the past few years have been due to such 
conditions. Heavy losses have resulted from decay not only in the 
field, but in apparently sound produce while in transit. This con- 
dition made it seem desirable to undertake a series of investigations 
with a view to determining whether some practical commercial 
method could be devised for reducing the losses that occur from the 
time the products leave the field until they reach the consumer. 
The Bureau of Plant Industry has conducted handling and pre- 
cooling investigations with several crops in other sections of the 
country, and similar investigations were begun with lettuce aud 
celery in Florida in the autumn of 1913. During the season of 1913-14 
particular attention was paid to the lettuce crop, and therefore this 
will be discussed first. 
LETTUCE-HANDLING INVESTIGATIONS. 
NATURE OF THE PROBLEM. 
The experimental work was done in the vicinity of Palmetto, in 
Manatee Comity, the center of one of the largest lettuce-producing 
sections of Florida. Lettuce has been grown there on a commercial 
scale for 15 years or more. In a great many cases it was found that 
lettuce had been grown year after year on the same land. As a 
result, practically all the cultivated fields in this section are infected 
with disease-producing organisms. 
Probably the most dangerous enemy of the lettuce crop is a fungus 
disease (Sclerotinia libertiana), 1 commonly known as lettuce drop, 
which causes tremendous losses yearly. Under conditions favor- 
able to the growth of the fungus, whole fields sometimes are destroyed 
within a short period of time. The first indication of the presence 
of the disease is a slightly wilted appearance of the lower leaves. 
The drop produces a discolored or watery area on the under sides of 
the infected leaves, and this is followed quickly by the appearance of 
white threadlike masses. The disease spreads rapidly throughout 
the head, causing it to collapse into a slimy mass. Infected leaves 
often may be found on heads that appear to be perfectly healthy, 
and sometimes it is impossible to find in a field a single plant that 
does not show some signs of infection. Figure 1 shows a field in 
which practically all the plants are affected with the drop. The 
wilted appearance of these plants as compared with those in the 
disease-free field shown in figure 2 is very marked. 
The general practice of most growers in preparing the lettuce for 
market is to cut off all plants close to the ground. The worst of the 
i Burger, O. F. Lettuce drop. Fla. Agr. Exp. Sta. Bui. 116, p. 27-32, 3 fig. 11913.] 
