[A] Condensed from an official report by J. H. Chittenden of the United States Department of Agriculture.
Asparagus is subject to the attacks of a number of fungi, the most widespread and destructive being the "rust," the cause of which is a fungus described by De Candolle as _Puccinia asparagi_ in the year 1805. From this it is seen that the rust upon the asparagus has been known to scientists for nearly a hundred years, and it is but reasonable to suppose that more or less of this fungus has existed beyond the history of man.
The first mention of asparagus rust in the United States was by Dr. Harkness, who claimed to have observed it on the Pacific Coast in 1880, although it is doubtful whether the genuine asparagus rust was ever found there. The first mention of it in the Eastern States was in the fall of 1896, and since then its range has been widening each year. Dr. Byron D. Halsted, of the New Jersey Experiment Station, was the first to call attention to it, and made it the subject of careful study. The results and conclusions derived from his experiments were published in a special bulletin, and from this the greater part of the following has been condensed.
[Illustration: FIG. 46--ASPARAGUS STEMS AFFECTED WITH RUST]
[Illustration: FIG. 47--PORTION OF RUSTED ASPARAGUS STEMS]
When an asparagus field is badly infested with the rust the general appearance is that of an unusually early maturing of the plants (Fig. 46). Instead of the healthy green color there is a brown hue, as if insects had sapped the plants or frost destroyed their vitality. Rusted plants, when viewed closely, are found to have the skin of the stems lifted, as if blistered, and within the ruptures of the epidermis the color is brown, as shown in Fig. 47. The brown color is due to multitudes of spores borne upon the tips of fine threads of the fungus, which aggregate at certain points and cause the spots. The threads from which the spores are produced are exceedingly small and grow through the substance of the asparagus stem, taking up nourishment and causing an enfeebled condition of the victim, 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.