This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
This differs from the ordinary Celery in having the stems swollen into a somewhat irregular turnip-like mass as shown (fig. 471), The "roots" attain a weight of 3 or 4 lb., and are cut up into slices and used in salads, for flavouring soups, etc. They are grown in smail quantities in some market gardens. The seed is sown in gentle heat in March and April, the little plants being afterwards pricked out 3 or 4 in. apart in boxes of light rich soil, or in an old hotbed. By the end of May, or early in June, they will be ready to plant in the open air, 1 to 1 1/2 ft. apart every way, in rich and deeply worked soil. The swelling of the stems is hastened in autumn by removing the lower leaves that are turning yellow; and from the end of September onwards they may be lifted and stored for use in dry, airy places; or they may be left in the ground if protected with litter, etc, till required.
Fig. 471. - Turnip-rooted or Knob Celery.
The Celery crop is liable to be attacked by maggot of the Celery Fly (Acidia heraclei, or, as it is better known, Tephritis Onopor-dinis). The insect (fig. 472) appears in April, and is of a tawny brown colour. The wings, which have an expanse of about 1/2 in., are transparent and iridescent, with oblique lines of brownish or rusty spots running through them. The larva varies from white to very pale green in colour, and has no legs. The eggs from which the larvae arise are laid singly upon the upper surfaces of the leaves of the Celery and also of the Parsnip, which is closely related botanically. The eggs hatch out in six or seven days, and the young maggots at once bore through the skin of the leaves into the tissues, the substance of which they feed upon, thus forming "mines" between the upper and lower surface. In about fourteen days the maggot changes into a pupa either in the leaf or in the soil. A few days later a new and perfect insect is hatched out, and several broods may be born in the course of the year, the last one, however, remaining in the puparium stage in the soil, or in pieces of stalk or leaf, during the winter.
From the nature of the attack the maggots must either be prevented from tunnelling in the leaves of Celery and Parsnips, as, when once inside, they can only be destroyed by picking off the diseased portions and having them burned. On no account should stalks or leaves of Celery and Parsnip containing grubs of the Celery Fly be thrown on the manure heap, as the pest will mature there as readily as elsewhere.
One of the simplest and best remedies is to spray the foliage early in the season with a mixture of soft soap and paraffin. A quart of paraffin and 1/2 lb. of soft soap, well churned up in warm water at first, and then diluted with water to 10 gall., makes an excellent solution. Large quantities, of course, would be necessary for field work, and it would be best to spray with a knapsack or other distributor. Two or three applications during the year may be necessary as a preventive.
Fig. 472. - Celery Fly (Tephritis Onopordinis).
1, Fly (magnified). 2, Lines showing natural size. 3, Larva and pupa figured on blistered leaf.
Another Celery pest is the Celery Stem Fly (Piophila Apii). The grubs of this tunnel down the blanched stalks and make rusty tracks. These not only disfigure the stems and render them more or less unsaleable, but very often also cause them to rot.