This is a fungus, and its name is Plasmodiophora Brassicae. It causes rough, gnarled, unwholesome swellings on the underground stem and roots, quite different from the white, ball-like growths caused by the gall weevil. It is usually very bad in light land districts, but far less troublesome where the soil is heavy. Obviously one step is to choose the heaviest soil at command, but often there is no choice, and the grower must make the best of what he has. A dressing of gas lime at the rate of 2 lb. per square yard, given in autumn or winter, left to lie on the surface for six or eight weeks, and then pointed in, is very good. Another plan is to earth up the stems when the crop is half grown, and so encourage fresh, healthy roots from the stems. Sowing in wood ashes is good. In sandy soil, where it is almost impossible to get a crop, it is often advisable to raise the plants under glass, and get them very strong before putting them out.
I have indicated that this and the club-root are totally different things. The gall weevil, Ceutorrhynchus sulcicollis, is a weevil that pierces the stems of green vegetables, and may also attack the roots, while in the case of Turnips it sometimes affects the whole bulb. Eggs are deposited, and grubs hatch, which feed and form galls varying in size from that of a Pea to a marble. The swellings are usually smooth, even, and whitish. Dressing with gas lime is good as a general remedy, as advised for club-root. In the case of all Greens it is wise to look over the plants when transplanting. It is an easy matter to slice the galls off into a box or pail, and draw the stems and roots through a puddle of soot and lime.
Late in summer large white butterflies are to be seen hovering over the Greens, and a few days afterwards a greenish grey caterpillar is seen feeding on the plants. The butterfly has laid eggs on the leaves, and the caterpillar has hatched from them. The small boy who is so fond of bringing down butterflies with his cap has a field for the exercise of his talents amongst the Greens if he can only be persuaded to interest himself in the matter. A few heavy showers do more than anything else to keep down the caterpillar. If they do not come opportunely, hand picking should be resorted to, backed up by dusting the plants with soot while they are wet with dew, or swilling them with brine. The ichneumon, a four-winged fly about 1/12 inch across, is the natural enemy of this Cabbage pest. Its maggots make yellow cocoons, which should never be destroyed.
Green vegetables are often iufested by aphides of one colour or another, and sometimes by the small white fly Aleyrodes proletella, which is called the Snowy Fly. It is almost a hopeless business to attack aphides in large breadths of Greens, and, happily, a soaking rain sooner or later comes to the rescue. The Snowy Fly is more difficult to get rid of, and I have found that much the best thing is to remove the lower leaves of the infested plants, so as to deprive it of its shelter, and destroy them.
Fig. 31. Club Root In Greens.
A, examples of club root in young plants of Broccoli: a, junction of plants with soil; b, sound portion of stem above ground; c, club or swollen portion of root-stem; d, tap root; e, fibres.
B, portion of healthy tissue from stem, showing cells with nuclei: f, cell wall; g, intercellular spaces.
C, section of a diseased part of root: h, destroyed tissue, usually dark coloured or blackish; i, exploited or swollen tissue.
D, piece of swollen tissue: j, cell completely tilled with protoplasm of parasite; k, cell with protoplasm of slime fungus advancing.
E, cell of Cabbage root occupied by spores, or resting stage of slime fungus: l, spores discharged by rupture of cell wall.