64 



CEREAL RUSTS OF THE UNITED STATES. 



oats : Avena sativa patula, A. sativa orientaUs, aud A.sativa nuila — culti- 

 vated varieties, aud DactyJis (jlomerata, aud Arrhenatherum elatius. The 

 followiug species may at preseut be cousidered as probable hosts : Avena 

 fatna, A. hoolceri^ A. pratensis, A. sterilis, Koeleria cristata, aud Lolium 

 perenne. 



Occurrence and distribution. — The black stem rust of oats is certainly- 

 more common thau the black stem rust of wheat, owiug probably to the 

 fact that oats matures later than wheat and the stem rusts occur later 

 than the other rusts. However, it is not known whether the stem rust 

 of oats is generally commoner thau the crown rust, although) definite 

 statements on this point might be made in the case of certain localities — 

 locality appareutly being an important feature in this connection. 



As in the case of stem rust of wheat, this rust is not constant in 

 occurrence, although perhaps more so thau the former. Reports indi- 

 cate that in the Southern States it is neither so common as it is in the 

 Northern States nor so common as the crown rust. iSTo trace of it was 

 seen in Maryland during two successive seasons of observations by the 

 writer. His examination of old straw at the Texas Agricultural Col- 

 lege in December, 1895, showed that the crown rust was quite abundant 

 the j)receding summer, but none of the stem rust was observed. 



Wherever oats is grown iu foreign countries the distribution of the 

 stem rust of oats seems to be quite general, but in some regions it is 

 said to be of little economic importance. 



Wintering of the uredo. — So far as yet known, this rust does not win- 

 ter its uredo in this country. The following table gives a summary of 

 the writer's observations of the occurrence of the uredo iu late summer 

 and autumn : 



Taulio 11. — Snmmanj of observatiouti on late ucciirrenre of Uredo f/raminis arcnce. 



The fact that the uredo was found on other hosts than oats, and espe- 

 cially the fact that .these hosts are perennial, strengthens the probability 

 that the uredo winters over, but at the same time weakens the proba- 

 bility that it winters on oats. At any rate, it is easily seen that orchard 

 grass and tall meadow oat grass are not likely to prove desirable 

 neighbors for the oat field. 



As already stated, Cobb (19, p. 29) mentions that P. graminis winters 

 over in the uredo stage iu Australia, but he is not sufficiently explicit 

 to justify the couclusion that he includes this form on oats. 



