370 Journal of Agricultural Research voi. xiii. no. 7 



There is one point which stands out plainly in connection with the pres- 

 ence in the soil of active bacteria able to produce widespread infection 

 in a lettuce crop in from three to six weeks. The worst infected field was 

 composed of soil heavily impregnated with a compost still in the middle 

 stages of decomposition (Pi. 30, A), and the plants were embedded in it 

 so loosely because of the unrotted stubble that their roots were not well 

 protected from the cold. The field was also unprotected by mndbreaks. 



In Beaufort County last year (191 7) a freeze in February destroyed all 

 the lettuce plants which had been set out in the early winter; but the 

 second crop, planted in the early spring, matured without any evidence 

 of this bacterial disease. A lettuce crop grown last spring in the area of 

 the 98 per cent loss was entirely free from disease. The weather condi- 

 tions remained favorable for growth during the season, and the plants 

 had no setbacks. As the soil necessary for the quick growth of lettuce 

 must be rich in decomposed organic matter, which likewise means one 

 rich in soil organisms, it is difficult, in a late-fall- or winter-grown crop to 

 eliminate the chance of these organisms getting into the plants should 

 there be temperatures low enough to weaken the plants but not to kill 

 them. Well-decomposed organic refuse, however, presumably has fewer 

 active organisms of parasitic types, and the chances for infection are less 

 should unfavorable weather conditions occur. 



THE VIRGINIA LETTUCE DISEASE 



An outbreak of disease on lettuce grown in soil rich in decomposing 

 organic matter occurred also in the lettuce-growing region near Ports- 

 mouth, Va., early in November, 191 6, following a heavy frost. At this 

 time the heads were of good size, well filled out, and nearly ready to 

 harvest. The disease was indicated by a spotting mostly on the outer 

 leaves, where the spots frequently coalesced, making dark brown, almost 

 black, widespread areas (PI. 31). In some cases the browning and 

 spotting ran along the midribs, but usually the infection was worse on 

 the blades. In other cases the tip ends of the heart leaves were stained, 

 but there was no definite spotting as in the outer leaves. The stems and 

 roots were not infected. Many of the heads were cut open in the field, 

 and the hearts were found to be all right, except for an occasional stain. 

 Cross-sections of young spots were examined under the microscope, 

 and bacteria were found in great numbers in the tissues. It seemed 

 evident that they had entered the plants while these were in a weakened 

 condition, and, getting a foothold, brought on the outbreak of disease 

 in less than three weeks after the heavy frost. The lower and outer 

 leaves, the parts most exposed to the cold, were the ones infected. 



In the Portsmouth region the writer visited four lettuce farms 

 where the disease was present, the loss varying from 10 to 40 per cent. 

 The growers in this section use a commercial fertilizer, but also fertilize 

 heavily with stable manure. This year they used fresh manure, the only 



