Turnip-gall Weevil
(see Turnip Galls) and Turnip-seed Weevil (which see). The best treatment for the destruction of these insects is mentioned under the above headings.
When the plants are somewhat larger, the leaves are often so eaten by numerous larvae, that merely the larger veins remain, or, at least, large holes are gnawed in the leaves and other green parts, to the injury of the plants, and the consequent diminution of the root-crop. The larvae (see Cabbage Caterpillars) of the White Butterflies (Pieris Brassicae, P. Napi, and P. Rapae) feed on the leaves of Turnips, as they do also on Cabbages; and they are assisted in this by the larvae of various Night-moths, e.g., of Mamestra (which see), and of Plusia gamma (which see) and others noted under the headings Potherb Moths and Surface Caterpillars. The larvae of a small Moth, Plutella cruciferarum (which see), are very numerous in some localities, living under webs on the lower surfaces of, and eating holes in, the leaves. Still more dangerous than the Butterflies and Moths is Athalia spinarum, the Turnip Sawfly (which see), the larvae of which at times devastate entire fields. An allied species (A. ancilla) also proves destructive occasionally, though to a less extent.
Various Beetles assist in destroying the leaves of Turnips, chief among them being the Turnip Flea (which see); though Curtis accuses Phaedon Betulae (which see) and Otiorhynchus of aiding in the harm done. Besides the holes eaten through them, the leaves are often marked with white, wavy tracks, or mines, burrowed between the surface-membranes. These mines are the work of larvae of small Flies (Drosophila and Phytomyza), and of the Turnip Flea (which see). The flowers inclosing the young ovaries are favourite resorts of numerous Beetles, some of which gnaw the various organs, devouring the ovaries, or rendering them unfertile. The flowers and flower-stalks, and, to a less extent, the leaves, are sometimes injured by more than one kind of plant-louse (see Aphides). The seeds are devoured in the seed-vessels, while soft, by larvae of certain small Midges belonging to the group of Gall-midges (Cecidomyidae), but these scarcely alter the form of the fruit. The larvae of the Turnip-seed Weevil (which see) also devour the seeds in the fruit. From their concealed mode of life, little, if anything, can be done against those insects that feed on the seeds. But, while the green parts, the flowers, and the seeds, are all liable to serious injury from animals, and the roots thus suffer indirectly, the latter parts suffer from direct attacks even more seriously than do the other organs. All herbivorous quadrupeds eat them; and hares and rabbits are peculiarly hurtful where Turnips are grown in an insufficiently inclosed area. Rooks also greatly injure Turnips, by scooping out holes in them to obtain food during snowy weather. In localities near the sea-coast, a similar habit is frequently indulged in by sea-gulls. Among the most effectual protections against birds are threads stretched in zigzags near the soil, and decked with rags, or other fluttering objects, suitable to act as scarecrows.
Some account of the more destructive parasites of Turnip roots is given, along with the most successful remedies against each, under the headings Slugs, Snails, Surface Caterpillars, Turnip Galls, Turnip Moths, and Wireworms; and it would occupy unnecessary space to repeat what is contained in those articles. When the roots have begun to decay, the change is hastened by numbers of Millipedes (which see) and insects (chiefly larvae of small Beetles and Midges) that feed in them, and soon reduce them to the condition of putrescent masses.
In Germany, it has been observed that Turnips and other Crucifers are liable to have the smaller side-roots more or less injured by the production of small, round galls on them, the work of a minute worm (Heterodera Schachtii), of which an account is given, and appropriate remedies are discussed, under Nematoid Worms.
Fungi. Turnips are liable to serious injury from the attacks of several species of Fungi, most of which have been already discussed in this work under headings quoted below. Almost all of them also infest Cabbages and cruciferous weeds--a circumstance that must be kept in mind in the means employed for preventing or curing diseases caused by them in Turnips. Of those that have proved peculiarly injurious in Great Britain, the more hurtful are the following:
Plasmodiophora Brassicae (which see), producing "Clubroot," or "Finger-and-Toe," in the roots, of which they cause the early death and decay, so that the crop is largely, if not entirely, destroyed in severe attacks. The leaves are frequently "mildewed." One form of "Mildew" is caused by the growth of the superficial mycelium of Oidium Balsamii (see Oidium), which is itself a young stage of an Erisyphe of some kind, of which the perfect condition is uncertain. The threadlike cells of the Fungus spread in a thin, whitish coat over the whole of both surfaces of the leaf, from which they draw their nourishment, without, however, traversing its tissues; and they injure it both by the nourishment they absorb from it, and by hindering free interchange of gases and fluid between the cells of its interior and the air. The leaves wither and dry up, and the plants are insufficiently nourished, with evil effects to the roots. For a remedy, see Oidium. Peronospora parasitica gives rise to another form of "Mildew" on the leaves. This shows itself in whitish patches, which consist of erect stalks, much branched above, and bearing on the tips of the branches the nearly globose conidia or reproductive cells. The mycelium of the Fungus burrows among the inner cells of the leaf, and only the stalks just spoken of are seen on the surface, passing out through the stomata. The sexual reproduction of the Fungus is also provided for by the mycelium in the leaves, as described under Peronospora. The upper surface of the leaves is mildewed by this Fungus far less frequently than the lower; but the presence of the parasite is shown by yellowish-green or yellow patches on the surface. P. parasitica frequently grows in the flower-stalks and in the flowers, which, under its influence, become much distorted and swollen, and fail to produce seeds. All parts in which it grows are liable to premature death and rapid putrefactive decay in moist air. For treatment, see Peronospora.
White Rust is very often associateu with P. parasitica, growing on the same spots of the plant, and actually intermingled with it; but frequently, also, they grow apart from one another. The White Rust resembles splashes of whitewash, when the conidia are matured on the diseased spots, which latter are usually swollen and distorted. It occurs on stems, leaves, and flowers. The Fungus (Cystopus candidus) is nearly related, in a good many points, to Peronospora. For an account of its structure, and of the treatment to be employed against it, see Rust.
The leaves frequently show spots or patches, often 1in. or more in breadth, at first yellowish, but soon becoming withered and dry. On these spots, the microscope shows minute Fungi. On some, there may be found slender conidia (with many septa, or cross-walls), on the tips of short threads, pushed through the stomata. This form of Fungus has been named Cercospora Bloxami by Messrs. Berkeley and Broome. On other spots occur small dark Pycnidia (which see), in which are produced small, oval, pale sporidia, one-celled (Phyllosticta Brassicae), or two-celled (Ascochyta Brassicae). The relations between the Fungi found on such patches are still very uncertain. Turnips do not suffer very seriously from the presence of these Fungi, as the latter seldom affect the young, vigorous leaves, but prefer the lower leaves when already half-dead. It is, therefore, unnecessary to dwell upon treatment, further than to mention that it is a wise precaution to destroy--if possible, by fire--all leaves overgrown with parasites.
Two other Fungi have been described as occasionally very injurious to Turnips in Germany, and a brief notice of them will not be out of place here. Polydesmus exitiosus is the name given by Dr. J. Kuhn to a Fungus described by him as extremely injurious to Turnips, destroying both the leaves and the unripe seed-vessels. Very dark spots appear on the diseased organs; the spots spread, and the tissues become discoloured, and dry up. If the seed-vessels are attacked while young, the seeds do not ripen; but if the disease is late in its appearance, they may ripen, but are soon destroyed, the valves of the fruit shrivelling, and bursting away prematurely. In the diseased tissues, the mycelium of a Fungus is present in abundance, absorbing the nourishment in the cells, and destroying the cell contents and cell walls. From this mycelium rise erect branches, which project through the epidermis of the leaf, and bear, on their tips, conidia that vary much in form, but that, when mature, are clavate, being fixed by the broader end, and having the other prolonged as a slender filament; or there may be a series of from five to ten such conidia, end to end, forming a chain. The conidia are dull or brown-violet, and are divided into cells, by numerous cross-walls, and a few longitudinal ones. The conidia readily fall off the erect branches, and germinate speedily, in damp, warm weather, spreading the disease if they fall on green parts of Turnip-plants, under suitable conditions. This Fungus produces brown, withered spots in the parts affected, often surrounded by a yellow or reddish border. On these spots develop Pycnidia (which see) of Phyllosticta Brassicae, and perithecia of a Pleospora (which see), perhaps P. herbarum. The only treatment possible is to endeavour to prevent future attacks, by destroying diseased parts of plants without delay.
Peziza sclerotiorum is blamed by Dr. Frank as the cause of a peculiar disease of Turnips, which was prevalent, near Leipzig, in 1879. The plants became yellow during July. The cause of this was a diseased state of the stems, commonly near the base, which manifested itself in a pale colour, and in a separation between the epidermis and the tissues below it. On breaking the stem, the pith is found occupied by a black, oval body, the sclerotium, from which the above Peziza grows out in the following spring. For an account of the structure of the Fungus, and of the treatment advised against it, see Peziza.
Sorts. These are very numerous, but it is unnecessary to grow many varieties if attention is given to include those which are adapted for early use, and others for main crops. The shapes and outside colours vary in the different sorts; but this is of little importance, provided the inner flesh is of good quality. The flesh is either white or yellow: white-fleshed varieties are generally preferred in the southern division of the country, while yellow ones are more largely cultivated in the north.
CHIRK CASTLE BLACK STONE, skin black; very fine and hardy EARLY PARIS MARKET, white, oblong in shape; early, a much-esteemed French variety. EARLY PURPLE-TOP MUNICH, distinct and very early; one of the most valuable for frame culture and for early crops, the produce is at its best when about half or three-parts grown. EARLY RED AMERICAN STRAP-LEAVED STONE flesh white and firm; very early. EARLY SNOWBALL, one of the best whites, sweet and tender; early, largely grown for the London markets. EARLY STRAP-LEAVED WHITE STONE, fine quality; suitable for very early and for late sowing (see Fig. 130). EARLY WHITE DUTCH, an old and well-known sort, of excellent quality. EXTRA EARLY MILAN, bulb flattened, with purple top; very early, and compact in habit. ORANGE JELLY, or GOLDEN BALL, an excellent yellow variety (see Fig. 131); much favoured in the north of England and in Scotland. VEITCH'S RED GLOBE, of handsome shape and fine flavour; one of the best for main crop, and for use in winter. YELLOW MALTA, a handsome yellow variety, of good quality, but sometimes rather strong-flavoured (see Fig. 132).
TURNIP FLEA, or TURNIP FLY. Names commonly given to two or three species of Phyllotreta (which see). This genus of small Beetles belongs to the large group formerly included under the generic name Haltica, but now, for convenience, subdivided, by minute characters, into numerous genera. All the insects in this group have the thighs of the hinder pair of legs thickened, whereby they are enabled to leap several inches. This power and their small size have gained for them the popular name of Fleas, though widely different from true Fleas in many respects. They all feed on plants, several being attached to the Cruciferae. Turnips are often ravaged by P. nemorum; and P. concinna is also a dangerous foe to these plants in some localities. P. consobrina and P. obscurella are mentioned by Curtis, in "Farm Insects," as not uncommon on Turnips; and P. flexuosa and P. Lepidii have been recorded as dangerous in Germany. However, the general appearance and the habits of all are much alike; as are also the remedies that should be employed against their attacks. The general form of the species in the genus is well shown in Fig. 133; but the size varies from 1/12in. to 1/8in. in length. All have the ground-colour very dark olive-green or metallic-green. P. nemorum has a broad ochre-yellow streak down each wing-case (see Fig. 133); and the legs are rusty-ochre, with pitchy thighs. P. concinna is more oval and convex than the former species, and is of a uniform greenish-black, with a shining coppery or brassy lustre--the legs being black, except the rusty-red base of the tibiae. P. consobrina, P. Lepidii, and P. obscurella, are much like P. concinna, the four species differing in the pitting of the surface, in the peculiar shade of the metallic lustre, in the colour of the base of the antennae, in the proportions of the fourth and fifth joints in these organs, and in size of body, to a slight degree. P. flexuosa is more like P. nemorum, being black, with a pale clay-yellow line down each wing-cover; but the pale line is narrow and wavy, and the knees are pitchy-black, not reddish; and the fourth and fifth joints of the antennae are shorter than in P. nemorum. An account of the life-history of the very common species P. nemorum may be regarded as fairly representative of the habits of all that attack Turnips; so that the following remarks, though referring primarily to that species, will also, in great measure, be applicable to the others. The Beetles usually pass the winter concealed under rubbish on the soil, e.g., stubble or other dead herbage, clods, &c., though an occasional warm day brings them out of their shelters. In spring, they begin to feed on the cruciferous weeds (Shepherd's Purse, &c.), which are only too plentiful everywhere, alike in cultivated ground and in waste spots. When the cotyledons and first leaves of the seedling Turnips appear above the soil, they form the favourite food of the Beetles, which gnaw away the tissues till little more than the skeletons of the leaves remain, and the plants die in vast numbers. The crops are occasionally ruined; and even second and third sowings are sometimes destroyed in the same way. After the young plants have produced the rough leaves, the danger of serious injury from this cause is comparatively slight; though large holes are gnawed by the insects in the leaves. The female beetles each lay a few white eggs, here and there, on the lower surface of the leaves. In about ten days, the larvae are hatched. They are pale yellowish maggots, with three pairs of legs in front, and a sucker at the end of the body. They gnaw through the skin of the leaf; and, for about a week burrow in the tissues below it. They then are full-fed, drop to the ground, and burrow from 1in. to 2in. into the soil, to become pupae. In about a fortnight, the beetles emerge. There may thus be, and usually there are, several broods in a season. Prevention and Remedies. It is most desirable to clear away all cover that can protect the insects. The ground should be cleared of all cruciferous weeds, such as supply the insects with food before the appearance of the Turnip crop. Digging and ploughing the soil in winter destroys many of the Beetles, by burying them too deeply to allow of their return to the surface. It should be kept in mind that the dangerous period to the crop is white the seedlings are quite young, and that the danger is very much less when the plants have formed the rough leaves; consequently, whatever strengthens the plants, and shortens the duration of the dangerous period, is a valuable means of preventing harm. It is, therefore, of great importance to have the soil thoroughly prepared before the seed is sown, as well as to give a good supply of manures, such as phosphates and nitrogenous manures, and also to water the plants in dry weather. It has been suggested that thick sowing (up to 10lb. of seed per acre) will give a better prospect of escape from complete loss by the Turnip Flea; but this is not advisable, as overcrowding is apt to render the plants weak, and to prolong the period of danger from the Beetles, as well as to do harm in other ways.
A method sometimes employed to protect Swedish Turnips, is to mix the seed with one-third of its weight of the seed of common Turnips, the young plants of which are preferred by the insects.
Should the crops be attacked, the injury may be lessened, even though a cure should not be effected, by one or other of the following methods: A light, shallow tray may be tarred inside, and dragged over the rows of Turnips, having something at such a distance in front as to disturb the insects, so as to cause them to leap into the tray when roused. Many can thus be caught, the tar holding them fast; or a large hand-net, such as entomologists use in "sweeping" for insects, may be made use of, the plants being swept with it. Rolling the ground in the early morning has been found beneficial, as has been also the treading of a flock of sheep, kept in constant motion in the field, for an hour or two, in the early morning. The latter operations should be carried out only while the dew is still on the herbage; and the same rule should be observed in the application of dressings of all kinds, as these are found to be far more efficacious if put on while the plants are wet. Soot may be sprinkled along the drills of Turnips; but the dressing that has given the best results is said to be made up as follows: One bushel of fresh gas-lime, one of fresh lime, ten pounds of soot, and six pounds of flowers of sulphur, mixed and powdered thoroughly, and applied broadcast or along the rows while the dew is still on. The above amount is enough for two acres. Another mixture also strongly recommended is two bushels of road-scrapings, one of fresh lime, and fourteen pounds of sulphur per acre, applied as above. TURNIP GALLS. The work of a small Weevil, which also forms somewhat similar Galls on Cabbages. A brief description of the Beetle (Ceuthorhynchus sulcicollis) will be found under Cabbage Gall Weevil (where, however, the name is spelt Ceutorrhynchus). To the particulars there given, a few words may be added. The colour of the insect is black, slightly shining, sprinkled with a few grey hairs, or small scales; the head and thorax are much punctured, and the latter has a deep median furrow, and a small prominence on each side; the wing-cases bear small prominences in front of the tips, and each thigh of the hindmost legs is toothed on the inner side. The length of body is 1/12in. to 1/8in. The females lay their eggs near the top of the roots of most Crucifers. In Turnips they do so a little above, or close to, the soil. In a short time, a Gall begins to appear, and at last its form and size may resemble a large half-pea fixed to the root by the flat side; or two or more may unite in growth. The Galls are fleshy, like the roots; and in each is a cavity, tenanted by a curved, whitish, footless maggot, which, when full-fed, bores its way out, drops to earth, and pupates 1in. or 2in. underground. This may be done in autumn, but the more backward larvae winter in the Galls. Remedies. The most certain is to cut off and destroy the Galls, with their occupants in them. Applications of soot or gas-lime, or other insecticides, to the soil whence infested plants have been lately removed, have proved valuable in lessening the prevalence of the Beetles. Other measures against injury will be found mentioned under Cabbage Gall Weevil.
TURNIP MOTHS. The larvae of several species of Moths feed on Turnip--plants, some preferring one organ, some another; but the insect which is usually denoted by the name of "Turnip Moth" is one of the Noctuae (see Moths and Noctua). Its scientific name is Agrotis segetum. The popular name is rather misleading, as the larvae feed on many other plants, including most root crops and numerous weeds. Moreover, several other Moths are almost as hurtful, in the larval state, to the roots of Turnips as is A. segetum. The genus Agrotis is a large one, and in the same species there may exist great variations in markings and shade of colour; while the species show a great general similarity to one another. The fore wings are long and rather narrow, and the hind wings are pale grey. A segetum (see Fig. 134) reaches 1 1/4in. to 1 2/3in. across the fore wings, which are grey or brownish, sometimes with a yellowish tinge; they are usually darker towards the front margin, and bear obscure, darker marks and cross-lines; the hind wings are pearly-grey. The larvae are of the form shown in Fig. 135; they are smoky-brown, tinged with pink or purple, with darker lines and small spots, and a paler line down the middle of the back; the head is small, and much narrower than the body. Owing to their habit of living concealed below the surface of the soil, the larvae are seldom seen. While young, they feed, in the darkness, above ground; and they are especially disposed to gnaw through the base of the stem in young plants, or to remove the bark, if the stems are too large to be gnawed through. They are indiscriminate feeders, devouring almost all kinds of herbaceous plants. In autumn, they often resort to Turnips, boring into the tuberous roots from below, and eating out large cavities, in which they live during the winter, or till food fails. A few become pupae, in cocoons in the soil, in October; but by far the larger number pupate in spring, and the moths emerge in June.
The Heart--and--Dart Moth (Agrotis exclamationis) is very similar to, and almost as destructive as, the Turnip Moth. The larvae of the two species are so much alike that it requires a skilled entomologist to distinguish the one from the other; but this is of little moment to gardeners and farmers, as they are as much alike in habits and in destructive powers as they are in appearance.
The larvae of a good many more species of Noctuae occasionally feed on the roots, leaves, or stems of Turnips, but they are so seldom the cause of perceptible injury to these plants that it is unnecessary to discuss them here.
Remedies. Such larvae as feed on the leaves of Turnips are best combated by the means detailed under Turnip Sawfly. Those larvae that frequent the roots are not easily reached when they have bored into the Turnips. The time when they can be destroyed, or kept in check, with most hope of success, is in autumn, while they are still living concealed during the day, but come out to feed at night. Hand-picking, by the light of a lantern, is too slow, except to protect choice plants. Soot and gas-lime have been found useful, applied round the top of the root of each plant; and the same is true of gas-water poured on the soil. Ploughing or digging the ground, during winter, is useful by turning up the larvae and exposing them to rooks and to other insectivorous birds, which are, in truth, the agriculturist's best allies against foes of this sort.
TURNIP SAWFLY (Athalia spinarum). One of the most dangerous enemies to Turnips in many years, since the larvae (known as "Niggers," or "Black Palmers," because of their dark colour) frequently appear in myriads in the fields, and devour the leaves of the young plants. Often a second sowing has been rendered necessary; and even a third or a fourth has been required at times. The perfect insects are Sawflies (see Tenthredinidae), about 1/4in. or 1/3in. long, and rather heavy in form. Their ground-colour is clay-yellow, covered with dense, whitish, short hairs. The antennae, head (except white mouth), spots on thorax, and tips of shanks and of joints of the feet, are black. The wings are transparent, with nerves (except at base) dark. The female lays about 250 eggs, often from ten to twenty on a single leaf, along the margins. The eggs hatch in from six to twelve days. The larvae at first are white, with two black dots on the head; but when nearly full-fed they are black above, paler below, with slate-coloured and black spots on the sides. There are usually several folds of skin, but no hairs, on the body. Often many occur on each leaf, and the leaves are gnawed away to the ribs by them. In about three weeks they reach their full size, and then burrow underground, and form oval cocoons. In these the summer broods lie about three weeks, when they emerge as Sawflies. There are usually three broods of Sawflies each year-in May, July and August, and September. They are partial to flowers, but also sit underneath the leaves of Turnips in dull weather, and may be caught by sweeping the plants with a net. They have been observed to proceed from district to district, beginning at one side of a field, and crossing it to the other, in regular succession. When the larvae are very numerous, the Turnips are almost wholly eaten down, and suffer so much that the crop is rendered nearly worthless.
Besides the well-known A. spinarum, another Sawfly does almost as much harm to Turnips in the larval stage. This is A. ancilla (also called A. glabricollis). The insects are much like A. spinarum; but their ground-colour is reddish or clay-yellow, and they are not hairy. The larvae of the two species are very much alike, and it is probable that those of A. ancilla are often wrongly ascribed to A. spinarum. The remedies recommended below are beneficial against both species.
Remedies. Disturbing the larvae when about to pupate, prevents this latter change, and the insect dies. It is also well to disturb them when changing their skins, as this is seriously hurtful to them, and destroys many. With this object, the plants may be brushed over with a rope, or with such branches as those of Firs, &c., and the larvae thrown to the ground may be crushed; or quicklime or gas-lime may be sprinkled on the soil around the plants. Anything that will promote the rapid growth of the Turnip-plants is valuable, as diminishing the risk of injury; hence, watering or irrigating the plants with liquid manure, or even with pure water alone, is advisable, and has the further advantage of being directly injurious to the larvae. Thick sowing is recommended, as part of the crop usually escapes, unless the larvae are excessively numerous; but it brings with it serious drawbacks. Ducks have been employed with advantage to reduce the numbers of larvae, and have, at times, saved the crops; but they are apt to suffer from eating the larvae in quantities, becoming affected with diarrhoea, and getting very thin.