414 Diseases of Economic Plants 



CARNATION 



Rust ''-^' ^-"^ (Uromyces caryophyllinus (Sch.) Wint.). — 

 The carnation rust was first described in 1789 in Germany 

 and was noted in the United States by Arthur in 1891, 

 evidently a recent importation. It rapidly became wide- 

 spread through sale of infected plants and cuttings and was 

 soon present in almost all greenhouses. Though widely 

 known in Europe, it did not seem to be especially destructive 

 there; but upon entrance into America its character changed 

 to that of an aggressive pest, and ruin was brought to the 

 beds in many greenhouses. The entire contents of large 

 houses valued at thousands of dollars was in many instances 

 utterly lost. After a short period of extreme destructiveness, 

 which was at its height about 1893, the vigor of the attack 

 waned, until to-day the pest does only a small fraction of 

 damage as compared with that of the early years of its inva- 

 sion, though it still causes one of the serious carnation 

 diseases. 



The rust is easily recognized b}' the sori filled with powdery, 

 brown spores. The sori, at first covered by the white epider- 

 mis, are 1-2 mm. in diameter, round or elongated in the 

 direction of the length of the stem or leaf. When very 

 numerous, the affected part is slightly bleached or yellowed 

 and appears swollen, owing to the much-ruptured epidermis. 

 The mycelium of the causal fungus is usually general through- 

 out affected plants, but may, in case of new infection, be 

 limited to the immediate region of the sorus. 



There is much difference in varietal resistance, a fact that 

 should receive due weight in the selection of varieties for 

 culture. 



Cuttings should never be taken from diseased stock. 

 If there is doubt as to the presence of superficial spores, it is 

 well to dip the cuttings in potassium sulfid, one ounce 

 to one gallon. A weekly protective spray of copper sul- 

 fate, one pound to twenty-five gallons, throughout the life 

 of the plant is also recommended. The leaves should be 



