Asparagus, its culture for home use and for market / A practical treatise on the planting, cultivation, harvesting, marketing, and preserving of asparagus, with notes on its history

by F. M. Hexamer

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.

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 fifty, making usually an oval spot easily 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 affected by the rust, although it has been found that some varieties, notably Palmetto, are less susceptible to its attacks than others. The most effectual means of controlling the disease are spraying, burning of the brush, cultivation, and irrigation.

Spraying.—Dr. Halsted, in his first experiments, used soda-bordeaux, hydrate-bordeaux, and potash-bordeaux. The spraying began June 2d, and ten sprayings were applied during the season. The applications were made with a knapsack pump, and therefore were far more expensive than they would have been if the sprayings were made with horse-power. With the fungicide costing $5.00 per acre, and a machine that would spray two or more rows at a time, it would be possible to reduce the cost to $10.00 per acre, or even less. In effectiveness the soda-bordeaux stood first. Between the other fungicides there was but little difference. The best results showed a reduction of rust of about one-quarter, which is not as satisfactory a result as had been expected.

In the spraying work conducted by Professors G. E. Stone and R. E. Smith, at the Massachusetts Experiment Station, the results were more encouraging. The solutions used were potassium sulfide, saccharate of lime, and bordeaux mixture. The spraying was done with a knapsack sprayer, provided with a Vermorel nozzle, and after the first application it became evident that the practice was of little importance on account of the difficulty in making the solution stick to the plant. For successful spraying of asparagus a finer nozzle is required than any that is now in the market.

In some other experiments carried out on a small scale the asparagus plants were practically covered with solutions, when they were put on with an ordinary cylinder atomizer, and the lime solutions showed excellent sticking qualities; but with the ordinary coarse nozzle the solutions would run off of the glossy epidermal covering of the plant very readily. Should the spraying of asparagus ever become a necessity, then some apparatus which can be strapped to a horse's back should be used. The narrow space between the rows forbids the use of the ordinary mounted appliances, and if spraying is to be carried on upon a large scale, it would be better to have the spraying mixture carried in some manner on the horse's back. In this way it would be possible to carry some thirty or forty gallons of mixture through the narrow rows.

Burning the affected tops.—There can be no doubt that by the burning of the infested brush, after the cutting season, innumerable rust spores are destroyed. But if this is done before the stalks are entirely dead new ones will spring up at once, and in a few days will be as badly affected as the first. The burning of the tops in the summer has, moreover, a decidedly injurious effect upon the roots, seriously weakening their vitality, and making the growth of the following year still more susceptible to the infection.

In the autumn, however, after the stalks are dead and dry, this damage does not prevail, and the spores upon old brush can be destroyed by burning the asparagus stems either as they stand in the field or by cutting and throwing the brush into piles. By the latter method many of the smaller branches will be broken off and scattered upon the ground, giving a suitable place for the spores to remain over the winter. For the same reason it is an advantage to burn the brush in autumn instead of the spring, and thus prevent the large loss of spores that would obtain. In other words, burn the plants as soon as they become brown and lifeless, for any delay means the breaking up of the brittle, rusty plants, and a heavy sowing of the spores upon the ground. If the fire could go over the whole field of standing brush, that would be the most effective destruction. At best, with these precautions, many of the spores will get scattered upon the soil, and it would be well to sprinkle a thin coat of lime upon the ground and leave it there during the winter. If this could be followed by a turning under of the surface soil in the spring, it would bury the spores that might still be living, so that they would be out of reach.

Cultivation and irrigation.—It has been observed that the injury to asparagus plants, as a result of rust, has been confined to dry soils, although there are places where beds in close proximity showed remarkable differences as to infection; and that robust and vigorous plants, even where cultivated on apparently dry soil, are capable of resisting the summer or injurious stage of the rust.