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
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.
In view of all the experiments so far made, and the experiences of
practical asparagus growers, Stone and Smith conclude that: "The best
means of controlling the rust is by thorough cultivation in order to
secure vigorous plants, and in seasons of extreme dryness plants growing
on very dry soil with little water-retaining properties should, if
possible, receive irrigation."
From a knowledge of the occurrences of the rust in Europe, and from
observations made in Massachusetts, they are led to believe that the
outbreak of the asparagus rust is of a sporadic nature, and is not
likely to cause much harm in the future, provided attention is given to
the production of vigorous plants.
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