10 



BULLETIN 1162, U. S. DEPARTMENT OF AGRICULTURE. 



OTHER EPIDEMICS. 



A 10-acre pasture at Clarion, Iowa, in which Rhamnus caihartica has 

 escaped from cultivation, has been under observation for the past three 

 years, although it was not studied in as much detail as the planting 

 at Hinton. The cultivated shrubs were 10 to 20 feet high, and the 

 escaped shrubs ranged from mere seedlings to a height of 4 feet. 

 During this 3-year period both the cultivated and escaped shrubs have 

 borne a?cidial infection, although only a maximum infection of 10 per 

 cent occurred on any of the shrubs. In the spring of 1921 a more 

 detailed study was made of this area. The aecidial stage appeared on 

 the Rhamnus leaves previous to the advent of the uredospore stage 

 on^oats. The oats adjoining the hedge showed the first crown rust 

 infection in this locality. The oats in the portion of the field farthest 

 removed from the hedge developed the least infection. All evidence 



Fig. •">.— Hedge of Rhamnus cathartic* near Hinton, Iowa. The oats adjoining this hedge had loo per 

 cent of crown-rust infection. The crop was barely knee high, many plants not heading. The 

 yield from this field did not pay the expense of harvesting. Photographed July 1, 1921. 



pointed to the fact that R. caihartica acting as an alternate host 

 caused the initial infection of crown rust on these oats. 



In August, 1919, and in July, 1920, and July, 1921, several oat 

 fields were inspected in the vicinity of Janesville, Avalon, Emerald 

 Grove, and Delavan Lake, Wis., where many shrubs of R. caihartica 

 have escaped from cultivation. Hedges were found along: the 

 roadsides, and seedlings were scattered throughout the vicinity. 

 During the springs of 1919 and 1921 the secidial infection was so 

 severe that the shrubs were entirety defoliated. In 1919 the oats in 

 the fields adjoining the buckthorns were not worth cutting. The 

 oats inspected within a 2-mile radius were severely injured. In 1920 

 the oecidial stage was again present on the bushes, and this infection 

 was disseminated to oats. The next year, 1921, witnessed another 

 severe loss in the yield of oats w T hich was traceable to infection from 

 the neighboring buckthorn shrubs. 



