The 12-spotted asparagus beetle (Crioceris 12-punctata) is a serious enemy sometimes. It is controlled in practically the same manner as the common asparagus beetle. The Asparagus miner (Agramyza simplex) sometimes causes damage. The adult is a small black fly, but the stalks are injured by the maggot, which mines under the skin in the lower part of the stalk. The eggs may be destroyed on lure or trap plants, which are burned in late June or early July.
Rust is practically the only disease that has caused any damage to asparagus. It made its appearance in this country in 1896, and has since caused heavy losses in almost all important asparagus-growing districts. Hexamer ("Asparagus," p. 138) describes this fungous disease as follows: "When an asparagus field is badly infested with the rust the general appearance is that of an unusually early maturing of the plants. 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 plants lifted, as if blistered, and within the ruptures of the epidermis the color is brown. 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 diseased 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".
Mowing and burning the tops every fall, after they become brown and lifeless, but before they have become brittle, is universally regarded as the best means of control. Plants of great vigor are not so subject to attack. In seasons of drouth the disease is especially troublesome, and irrigation is considered a means of reducing loss from this malady. Some plants are more resistant to rust than others, and this fact has led to the establishment of a breeding station at Concord, Mass., where investigations and experiments are being made under the direction of the United States Department of Agriculture. It is hoped that new varieties which will be entirely immune from this dreaded disease will be developed.