. Bulletin of the Department of Agriculture. Agriculture; Agriculture. BACTERIAL WILT OF CUCURBITS. 33 coupled with prolonged temperatures at or above the maximum for growth of the wilt bacteria will reduce the percentage of infection and rate of progress of the disease, and in extreme cases the wilt may be even practically stamped out. However, under ordinary field condi- tions in the Northern and Middle States, the limiting factors appear to be (a) the presence of wilt-carrying beetles and (&) a vigorous, succulent growth condition in the host. Certain data relative to the incubatio
. Bulletin of the Department of Agriculture. Agriculture; Agriculture. BACTERIAL WILT OF CUCURBITS. 33 coupled with prolonged temperatures at or above the maximum for growth of the wilt bacteria will reduce the percentage of infection and rate of progress of the disease, and in extreme cases the wilt may be even practically stamped out. However, under ordinary field condi- tions in the Northern and Middle States, the limiting factors appear to be (a) the presence of wilt-carrying beetles and (&) a vigorous, succulent growth condition in the host. Certain data relative to the incubation period of the wilt organism have been compiled from our inoculation experiments and field records. Among 295 sets of greenhouse inoculations on cucumber seedlings, in each case using two or more plants 6 to 18 inches high, the great majority showed signs of wilt in 4 to 6 days after needle-prick inocu- lation, wilting of the first leaf in 5 to 8 days, and complete wilting of. FIRST SIGNS OFWILT WILT OF FIRST LEAF WHOLE PLANT WILTED >v?^. NUMBER OF DAYS 30 40 =* ,J< Fig. 7.—Diagram showing the progress of wilt in 295 inoculation tests on cucumbers (mostly the Arlington White Spine variety), with two or more plants in each test and in all using 103 different isolations of Bacillus tracheiphilus. the plant in 11 to 15 days (fig. 7). Comparatively few of these cucumber plants took more than three weeks for complete wilting, and out of the whole 295 experiments only 6 exhibited any cases of recovery after once showing signs of the disease. Upon reference to the notes it was found that our 5 least virulent isolations (En 15, R 235, R 311-a, R 317, and En 160) had been used for inoculation in these 6 experiments. These 5 isolations were all low in virulence, but, with the exception of R 317, they usually caused complete wilting of a plant in the end. In 51 inoculation tests on squash seedlings 6 to 12 inches high most of the plants showed incipient wilt in 5 to 8 days, wilti
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