. Control of bacterial wilt (Bacterium solanacearum) of tobacco as influenced by crop rotation and chemical treatment of the soil. Tobacco Diseases and pests. CONTROL OF BACTERIAL WILT 9 Table 2.— Wilt on tobacco grown on large plots in 1939, after 3 years of another crop Crop grown for 3 years before tobacco Tobacco Native weeds Crabgrass Sweetpotato_ Redtop 2 Corn Tobacco plants wilted August 1 Percent i 100 84 91 75 59 41 Acre yield of tobacco Weight Pounds 0 298 340 473 733 Value Dollars 0 120. 51 129. 52 1 Approximately 800 plants per plot. 2 Sudan grass (Sorghum vulgare
. Control of bacterial wilt (Bacterium solanacearum) of tobacco as influenced by crop rotation and chemical treatment of the soil. Tobacco Diseases and pests. CONTROL OF BACTERIAL WILT 9 Table 2.— Wilt on tobacco grown on large plots in 1939, after 3 years of another crop Crop grown for 3 years before tobacco Tobacco Native weeds Crabgrass Sweetpotato_ Redtop 2 Corn Tobacco plants wilted August 1 Percent i 100 84 91 75 59 41 Acre yield of tobacco Weight Pounds 0 298 340 473 733 Value Dollars 0 120. 51 129. 52 1 Approximately 800 plants per plot. 2 Sudan grass (Sorghum vulgare var. sudanense (Piper) Hitchc.) grown in the summer of 1936 and redtop (Agrostis alba L.) seeded in the fall of that year. Wilt increased about 100 percent on all rotated plots later in the season. For example, tobacco grown after the redtop and corn rotations had 59 and 41 percent wilted plants on August 1, 90 and 74 percent by September 1, and by October 1 nearly all the plants were dead on both plots. It was apparent that the increased yields resulted not from elimination of the disease but from a delay in its development until the greater part of the crop was harvested. Experiment on Single-Row Plots The foregoing experiments were conducted on plots protected from reinfesta- tion. Marked differences were obtained from crop rotation on unprotected plots. In 1936 several varieties of velvet bean were grown in rows 4 feet apart to test their susceptibility to wilt by natural infection, and a row of tobacco was planted in the middle as a control. All the tobacco was killed by wilt, but the velvet- beans remained healthy. In the fall of 1936 and the spring of 1937 the entire area was plowed and harrowed flat. Tobacco was planted and cultivated in the usual way without any effort to prevent the spread of wilt from row to row. The differences were striking in the earlier part of the season, as shown in figure 3, photographed July 21, 1937. By August 15, however, all plants were
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