Journal of Agricultural Research . Journal of Agricultural Research Washington, D. C. PLATE 6 A.—Rootrot spot, approximately 7 meters in diameter, in an alfalfa field, Septem*ber 18, 1921. B.—The same spot June 18, 1922, at the beginning of seasonal activity, approxi-mately II meters in diameter. C.—The same spot July 6, 1922, at the point of conjunction with another infecterispot. D.—Rootrot circle 18 meters in diameter in alfalfa field, Sacaton, Ariz., 1923.Conidial mats several days old are shown near the periphery, and the zone of activedisease has advanced beyond them. A whitewash solutio
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Journal of Agricultural Research . Journal of Agricultural Research Washington, D. C. PLATE 6 A.—Rootrot spot, approximately 7 meters in diameter, in an alfalfa field, Septem*ber 18, 1921. B.—The same spot June 18, 1922, at the beginning of seasonal activity, approxi-mately II meters in diameter. C.—The same spot July 6, 1922, at the point of conjunction with another infecterispot. D.—Rootrot circle 18 meters in diameter in alfalfa field, Sacaton, Ariz., 1923.Conidial mats several days old are shown near the periphery, and the zone of activedisease has advanced beyond them. A whitewash solution was applied to the matsto facilitate photographing. The white stakes indicate the furthermost margin ofactive disease the previous year. PLATE 7 A.—Segregated rootrot area i6 days after treatment with formaldehyde. No plantsoutside the original area had died since treatment. B.—Control area of approximately the same original size; the disease had advanced6i cm. in i6 days. C.—The rootrot area shown in Plate 7, A, 6