1020] 



DISEASES OF PLANTS. 547 



Stiitinn on tlie mosaic disease of Irish potatoes. Transmission of the potato 

 mosaic was found to take phice by means of tubers, grafting, tlie transfer of 

 plant juice, and aphids under various conditions. Infection was also obtained 

 with intervarletal transfer of juice. Transmission was attempted, but wltliout 

 success so far as could be ascertained in the same season, by means of Ilea 

 licetles, Colorado potato beetles, the seod-cutting knife, and contact of seed 

 pieces, of roots, and of vines. 



Preliminary observations arc believed to indicate that infection does not re- 

 sult from growth in soil that produced mosaic plants the previous season. It 

 seems impossible either for infected plants to recover, or if diseased stock is 

 not far away and insect carriers exist, to assure the maintenance of health 

 of susceptible varieties by roguing plats or by selection of hills, tubers, or seed 

 pieces. Isolation of plants by means of insect cages, as well as growing potatoes 

 in greenhouses in which insects were excluded, maintained stocks free of dis- 

 ease. This is believed to indicate that the control of aphids and possibly some 

 other kinds of insects is the most important means of checking the spread of 

 potato mt)saic among susceptible varieties. 



The source of tlie primary field outbreak of potato late blight, J. Eriks- 

 son {Arkii: Dot., IJ, (1916), No. k, ^'^rt. 20, pp. 1-72, pis. 6, figs. 5).— The author 

 here deals with the development of potato late blight {Phytophthora infcstans) 

 in considerable detail, somewhat as in a report previously noted (E. S. II., 39, 

 p. G50). 



Wilt diseases [of potato], H. A. A. van der Lek (Tijdschr. Plantensiekten, 

 24 (1018), Xo. 6, pp. 205-21<J, pi. 1; 25 U'JlO), No. 1, pp. 11-52, pis. 2).— This is 

 a review of wilt diseases of potato with particular reference to that caused by 

 Verticillium alhoatrum, which is discussed in connection with lists of its hosts 

 in Europe and America, its effects on potato, its distribution, and its control. 

 Treatment of seed potatoes, D. C. George (Ariz. Comn. Agr. and Hort. 

 Ann. Rpt., 9 (1917), pp. 67, 68, pi. 1). — The most important potato diseases in 

 Arizona are said to be Rhizoctonia and scab, which are compared to show resem- 

 blances and differences. They are controlled by the same sort of seed treat- 

 ment, namely, 1 per cent corrosive sublimate solution. Formaldehyde is effec- 

 tive against scab, but not very satisfactory against Ilhizoctonia. 



Effects of Bordeaux mixture on potato plants, .1. R. Bos (Tijdschr. 

 J'liintcnzichtcn, 25 (1919), No. 2, pp. 77-94). — Aside from any control exerted 

 as regards Phytophthora infestans, Bordeaux mixture has a decided beneticial 

 effect on the plant itself. This the author is inclined (as the result of work 

 to be continued) to attribute to the protection afforded to the plant against 

 overinsolation and to consequent increase of assimilation, as well as to the 

 longer period of growth in sprayed plants. 



Spinach blight and its transmission by insects, L. B. Smith (Rpt. State 

 Ent. and Plant Path. Va., 11 (1916-17), pp. 40-58, figs. 6).— A more extended 

 account of this disease, as given by the author and McClintock, has been noted 

 from anotlier source (E. S. R., 30, p. 550). 



Artificial and insect transmission of sugar cane mosaic, E. W. Bkandes 

 (Jour. Agr. Research [U. S.], 19 (1920), No. S, pp. lSl-138).— In a contribution 

 from the Bureau of Plant Industry, U. S. Department of Agriculture, the 

 author gives an account of experiments conducted to determine if possible 

 the means of transmission of the mosaic or mottling disease of sugar cane. 



Some healthy plants were grown near but not touching diseased ones. In- 

 sect visits were permitted, with the result that evidence of mosaic appeared 

 on the sound plants after a period of approximately a month. Plants 

 screened against insects remained healthy. Sorghums and various grasses 

 were also found to be affected by the disease. The corn aphis {Aphis maidis) 



t 



