368 Journal of Agricultural Research voi. xiii, no. 7 



THE SOUTH CAROLINA LETTUCE DISEASE 



The South Carolina outbreak of lettuce-rot occurred in Beaufort 

 County, the second largest lettuce-growing district on the eastern coast 

 of the United States, with a reputation of growing the finest quality of 

 Big Boston head lettuce on the entire eastern coast. The South Caro- 

 lina disease may be either a stem or a leaf infection (PI. 29, A, B). In 

 an early stage the plants are a lighter green color than the healthy ones; 

 later the head may show rot through the center or only on the top. A 

 general wilting of the head may occur with or without visible spots or 

 rot. In some cases rotting is rapid; in others the heart remains sound, 

 while the outer encircling leaves are in a bad state of decay. The dis- 

 eased plants are not firm in the soil, the stem is brittle, and can be easily 

 broken off at the surface or a little below the surface of the soil. In an 

 early stage of disease the stem when cut across shows a blue-green color; 

 in a later stage it is brown. If the disease attacks a young plant, no 

 head will form. There are also cases where the stem remains sound, and 

 only the leaves are affected, those leaves having definitely outlined spots. 

 In others the spots have coalesced, making a darkened mass of diseased 

 tissue. A condition of hollow stem accompanied many of the diseased 

 plants, but there were many plants without the disease which also had 

 the hollow stem. This hollowness of the stem at the surface of the 

 ground or just below it may have been due to unequal growth which fol- 

 lowed a sudden check of rapid development or of regular growth. The 

 effect of the hollow stem was varied : Some sound heads were produced ; 

 other plants were stunted; still others formed no heads. Where there 

 was no discoloration in these hollow stems, no bacteria were found. 



The different farms showed variable amounts of the lettuce disease. 

 On one particular farm of 9 acres there were heavy losses. A patch of 

 2,/4 acres on this farm was examined very carefully by Dr. Joseph Rosen- 

 baum, of the Bureau of Plant Industry, and by actual count 98 per cent 

 of the plants were diseased (PI. 30, A). Another farm of 17 acres suf- 

 fered a loss of at least 60 per cent on a conservative estimate. On other 

 farms visited the loss was much less, varying from i to 1 5 per cent. 



The direct cause of the disease was thought to be a sudden drop in 

 temperature which occurred the middle of February, when the mercury 

 fell to 22° F. The plants were set out in December and January from 

 perfectly healthy seed beds. 



On examining into the different cultural and soil conditions on the 

 various Beaufort farms several facts were brought to light. The soil 

 throughout that locality is a sandy loam; the fertilizer used was made from 

 marsh sedge, marsh mud, and leaf mold from swamps (live-oak leaves, 

 etc.) composted with cattle, mule, and hog manure. To be in good con- 

 dition for use, this compost should be allowed to decompose for two years 

 because of the fibrous condition of the marsh sedge and the acidity of 



