POPLAR DISEASES 303 



Cause. 



The poplar canker is caused by the fungus Dothichiza populea, 

 which has apparently not previously existed in this country. 

 It is supposed to have been brought into the United States on 

 affected nursery stock from France or Italy where it is common. 

 An Italian investigator has proved that this fungus has an as- 

 cospore stage which is called Cenangium populneum Rehm. 

 So far, this ascomycetous fungus has not been associated with 

 the poplar canker in this country, although it is supposed to 

 have been present here as a saprophyte for many years. The 

 Dothichiza stage on the cankers is a pycnidial stage. The spores 

 which appear temporarily glued together in the spore-tendrils, 

 pushed out from the pustules on the diseased bark, are probably 

 mainly disseminated by the rain. Also birds and various 

 animals which come into contact with the tendrils may carry 

 the spores on their bodies. This disease is similar in many 

 respects to the Endothia canker of chestnut (see page 140). 



Control. 



Trees from nurseries may bring this disease into new locali- 

 ties. Care should be taken to eradicate all dead and cankered 

 twigs from stock recently obtained from nurseries. In case the 

 disease appears on older trees, pruning off the diseased limbs and 

 cutting out the cankered area are the only control measures 

 known. For directions for carrying out these types of eradica- 

 tion measures, see page 345. 



References 



Hedgeock, Q. G., and Hunt, N. R. Dothichiza poptdea in the United 



States. Mycologia 8 : 300-308, pis. 194-195. 1916. 

 Voglino, Piero. I nemiei del Pioppo oanadense di Santena. Nemici 



vegetale. Ann. R. Accad. Agr. Torino. 53 : 325-377, figs. 1-4. 



1911. 

 Delacroix, Georges. Une maladie du Peuplier de la Caroline. Bui. 



Soc. Mycol. Prance 22 : 239-252, pi. 1. 1906. 



