Sept. 17, 1917 Mosaic Disease of Tobacco 629 



In several instances the plant louse Macrosiphum tahaci has become 

 established in the seed beds at Arlington, and appears to have been asso- 

 ciated with outbreaks of the mosaic disease which appeared in the 

 infested areas. 



Under greenhouse conditions experiments indicate that plant lice may 

 become important disseminators of infection. Experience has also 

 shown that the occurrence and spread of the disease in the greenhouse 

 can not be controlled so long as the plant louse Myzus persicae is allowed 

 to multiply unchecked. 



If plant lice are excluded by fumigation, however, the occurrence and 

 spread of the mosaic disease of tobacco becomes a negligible factor, pro- 

 \dded contamination of the plants in the process of handling does not 

 take place. Although white flies {Aleyrodes vaporariorwrn Westw.) are 

 also troublesome pests upon tobacco in the greenhouse, they do not 

 appear to be actively concerned with the spread of the disease. Pre- 

 liminary experiments with these insects, obtained from mosaic-diseased 

 plants and confined upon healthy plants in screened cages, have also 

 given negative results. Red spiders (Tetranychus telarius L.), which do 

 not take kindly to tobacco, have given the same results. 



Although in the United States plant lice do not appear to be especially 

 troublesome pests on tobacco in the field, it appears that they sometimes 

 cause serious injury to tobacco in Europe and elsewhere. Preissecker * 

 states that during some seasons they fairly cover the leaves of tobacco 

 plants and produce far more injury than is usually estimated. It is 

 especially interesting to note that Preissecker ^ has also observed that the 

 mosaic disease of tobacco is associated with attacks of plant lice.. 



Die von Blattlausen verwundeten Blatter sind begreiflicherweise spater gewohnlich 

 auch von anderen Krankheiten (Pilzen, Mosaik- und Pockenkrankheit) viel mehr 

 heimgesucht als die unbeschadigten, und es ist deshalb von allem Anfange auf die 

 Entfernung und Femhaltung der Blattlause ein besonderes Augenmerk zu richten. 



Preissecker again discusses the widespread occurrence of plant lice 

 upon tobacco in the Imoskaner region in a later article,^ and mentions 

 that the species Myzus plantaginis Pass, is very common on tobacco in 

 Dalmatia. Other species are also mentioned. He states that plant lice 

 are especially injurious to young plants in the seed bed. Concerning the 

 abundance of plant lice upon tobacco in the field, he' says: 



Im Jahre 1903 gab es von Anfang Juni bis zur Emte Blattlause auf Tabak im ganzen 

 Imoskaner Bezirke; man traf Pflanzungen in denen jeder Stock on alien Mutter- 

 und- Spitzblattem, u. zw. meist aiif beiden Seiten derselben, von den Lausen so 

 dicht besetzt war, dass sie hier tmd da iibereinander kriechen mussten, um Platz zu 

 finden. . . . 



' Preissecker, Karl, ein kleiner beitrag zur kenntnis des tabakbaues im imoskaner tabak- 

 BAUGEBIETE. In Fach. Mitt. Oesterr. Tabakregie, Jahrg. 3, Heft 2, p. 1-31, 19 fig. 1903. 



2 Preissecker, Karl, ein kleiner beitrag zur kenntnis des tabakbaues im imoskaner tabak- 

 BAUGEBIETE. In Fach. Mitt. Oesterr. Tabakregie, Jahrg. 5, Heft i, p. 1-44, fig. 41-75 (i pi.). 1903. 



