CHAPTER I. 

 BLIGHTS. 



STEM BLIGHT OF ALFALFA. 

 Pseudomonas medicaginis Sackett, 



HISTORY AND DISTRIBUTION. The disease has been known in Colo- 

 rado since 1904 and was described briefly by Paddock in 1906 and more 

 fully by Sackett in 1910. It is distributed generally over Colorado, 

 and is reported to occur in Utah, New Mexico, Nevada, Nebraska and 

 Kansas. 



SYMPTOMS. The disease is primarily a stem infection. In the 

 earliest stages, the stems have a watery, semi-transparent, yellowish to 

 olive green appearance along one side. Soon there oozes from the dis- 

 eased tissue a thick, clear, viscid liquid which spreads over the surface 

 and collects here and there in little bead-like droplets. This exudate 

 dries in a short time with a glistening finish, and gives the stems very much 

 the appearance of having been varnished, and where the liquid has col- 

 lected in little amber-colored scales and has hardened, it looks as if the 

 varnish had run and dried. Stems in this condition have a dry, slightly 

 rough feel to the touch. The exudate also dries uniformly over the surface 

 or just beneath it, and there produces a dark brown, resinous surface 

 which blackens with age. Such stems are very brittle and easily broken, 

 which fact makes it almost impossible to handle the crop without an 

 immense amount of shattering. The leaves attached to the blighted 

 stems usually show the disease, and sometimes they exhibit the infection 

 independent of the stem. In this case, the petioles become watery and 

 pale yellow, then droop. The malady may be confined to the petiole and 

 base of the leaflet, or it may involve the whole of the blade. Occasionally 

 leaves are found where the inoculation has been made, apparently, in 

 the margin of the leaflet, and the infection has proceeded toward the 

 middle. In such instances, the tender tissue has a watery look, as if 

 it had been bruised. 



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