2 BULLETIN 601, U. 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 and 

 celery in Florida in the autumn of 1 9 1 3 . During the season of 1 9 1 3-1 4 

 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 County, 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 (Sderotinia libertiana) , j commonly known as lettuce drop, 

 which causes tremendous losses yearly. Under conditions favor- 

 able to the growth of the f magus, 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 groimd. The worst of the 



i Burger, O. F. Lettuce drop. Fla. Agr. Exp. Sta. Bui. 116, p. 27-32, 3 fig. [1913.] 



