140 ASPARAGUS 



taking up nourishment and causing an enfeebled con- 

 dition of the vidlim, which results in loss of the green 

 color and the final rustiness of the plant, due to the 

 multitude of spores formed upon the surface. These 

 spores are carried by the wind to other plants, where 

 new disease spots are produced ; but as the autumn 

 advances a final form of spore appears in the ruptures 

 that is quite different in shape and color from the first 

 ones produced through the summer. The spores of 

 late autumn, from their dark color, give an almost 

 black appearance to the spots. 



There is another form which the rust fungus assumes 

 not usually seen in the asparagus field, but may be 

 found in early spring upon plants that are not subjected 

 to cutting. This is the cluster-cup stage, so named 

 because the fungus produces minute cups from the 

 asparagus stem, and in small groups of a dozen to 

 fift\', making usually an oval spot easilj' seen with the 

 naked eye. This stage of the fungus comes first in 

 the order of time in the series, and is met with upon 

 volunteer plants that may grow along the roadside or 

 fence row, or in a field where all the old asparagus 

 plants have not been destroyed. 



METHODS OF TREATING THE RUST 



All the cultivated varieties of asparagus are readily 

 affedled by the rust, although it has been found that 

 some varieties, notabl}- Palmetto, are less susceptible 

 to its attacks than others. The most effecflual means 

 of controlling the disease are spraying, burning of the 

 brush, cultivation, and irrigation. 



Spraying. — Dr. Halsted, in his first experiments, 



