California aster yellows on vegetable and seed crops

does not appear. First page follows. Introduction The investigations of host plants of aster yellows are covered by three reports. The present paper is confined to the work with aster yellows on vegetable and seed crops. One other paper in this issue describes the disease on ornamental flowering plants (Severin and Freitag, 1945). Weeds experimentally and naturally infected are discussed in a third paper (Frazier and Severin, 1945). In 19024 Smith described aster yellows, especially as it affects the flower; he was the first to notice it in California. The disease is now generally distributed in most counties of the state. Among economic plants, celery is seriously affected (Severin, 1929a) in certain years. During 1931 a general outbreak occurred in the Sacramento Valley, and celery in many fields was plowed under. Lettuce, carrots, parsley, parsnip, and potato (Severin, 1929a), (1932), (1940) have been demonstrated to be naturally infected; but the disease is of no economic importance at present. Field investigations of other host plants of this virus were conducted from 1925 to 1943. Several new vegetable host plants were noted, as recorded in this paper. The infection of seed crops received special attention, and surveys were made of seed farms and the ranches of seed companies. Attempts were made to recover the virus from naturally infected host plants. The symptoms were studied. Methods The method of recovering the virus from naturally infected host plants and the production of noninfective leafhoppers were the same as in previous investigations (Severin 1929a), (1942). A detailed account of methods is given in the third paper of this series (Frazier and Severin, 1945).