THE FUNGUS PESTS OF CERTAIN GARDEN PLANTS

Many of our garden plants are liable to the attacks of fungi. Cures are in most instances unknown, but in some cases preventives--which are better--have been adopted with partial or entire success. Plants raised from robust stocks, grown in suitable soil and under



favourable conditions, are known to be less liable to disease than seedlings from feeble parents, or those which have been rendered weakly by deficiencies in the soil or faulty cultivation. Whether weakness is hereditary, or is attributable to a bad system, the fact remains that disease generally begins with unhealthy specimens, and these form centres of contamination from which the mischief spreads. It is, therefore, important that seed from healthy stocks should be sown, and that a vigorous constitution should be developed by good cultivation. Anbury, Club, or Finger-and-toe.--The disease known by these various names is common in the roots of cultivated cruciferous plants such as Cabbages, Kohl Rabi, Radishes, Swedes, Turnips, &c., and also in many cruciferous weeds, including Charlock and Shepherd's Purse. The cause of this disease is an extremely minute fungus, which may lie dormant in the soil for several years for want of a comfortable home, and when a cruciferous plant becomes available the fungus fastens on the fine roots, multiplies rapidly in the tissues, and produces malformation and decay. After the disease has made some progress insect agency frequently augments the mischief, so that on cutting open a large decaying root it is not unusual to find the interior packed with millipedes, weevils, wireworms, and other ground vermin. Unlike the Potato disease, which spreads from plant to plant through the atmosphere, the fungus of Finger-and-toe infects the ground, and from the first spot attacked the disease spreads rapidly in all directions and in various ways. It may be carried by the soil adhering to implements or the boots of labourers. And each patch becomes a new centre of infection which is spread by digging or raking. Every scrap of infected soil, or of diseased fibre which may be added to the manure-heap, distributes the virus over a wider area, so that Finger-and-toe may suddenly appear in parts of the garden which have hitherto been free from this troublesome pest. A very simple experiment will prove the certainty and ease with which the spores may be introduced to fresh land. Macerate the tissue of old Finger-and-toe in water; use this on young isolated plants of Cabbage or Turnip and in a short time the plants will be infected. The fungus which produces Finger-and-toe is known as Plasmodiophora brassicae, and it belongs to the Myxomycetes, or {~~}slime-fungi,' which, as a rule, live upon decaying vegetable material. The protoplasm of the fungus ramifies among and within the tissues of the roots of attacked plants, and eventually produces an amazing number of spores so small that more than thirty millions would be required to cover a superficial inch. A microscope of great power is necessary to reveal them to human vision. [Illustration: FUNGUS OF FINGER-AND-TOE DISEASE Plasmodiophora brassicae] The spores are capable of resting in a state of vitality for a long time, and can easily withstand the frosts of winter. The illustration shows at A the fungus in its protoplasmic condition, and at B its ultimate sporiferous or 'seed'-producing stage, after the protoplasm has changed to a mass of minute spores (enlarged five hundred and twenty diameters). When a spore in due course germinates, its protoplasmic contents escape through a small aperture in its wall and begin moving about of their own accord in a slow writhing manner. The movement is so much like that of the microscopic animal organism found in ponds, and called Amoeba, that this tiny mass of moving protoplasm is called Myxamoeba, to denote that it is an amoeba-like form produced by one of the Myxomycetes. Each myxamoeba is drawn out at one spot into a fine delicate tail or cilium, as at C, D, E, and is capable of a creeping motion in moisture. When quite free from the spores, transparent expansions or limbs extend from the bodies of the myxamoebae, as at F, G, and when these organisms, after existing in the soil for a longer or shorter time, reach the roots of cruciferous plants, which they apparently enter through the root-hairs, they again assume the protoplasmic condition shown at A, and live within the cells, at the expense of the nurse-plant. Other cruciferous plants are less seriously damaged by the pest than are Turnips and Cabbages; but it is evident that if diseased Charlock is near Turnips, the latter are very likely to fall a prey to the disease. We advise the sowing of the best seeds, the eradication of cruciferous weeds, and the destruction by fire of all decaying Finger-and-toe material, for it is in this material that the spores of the disease rest ready for continuing the disease in the following season. It is also desirable that cruciferous plants should not be continuously grown in the same quarter--in other words, it would be prudent after an attack of Anbury not to repeat a cruciferous crop on the same ground, but to follow on with a crop of some other class. Numerous experiments have shown that slaked lime can be relied on to destroy the spores of Finger-and-toe in infested land. An application of from fourteen to twenty-eight pounds per pole may suffice in the case of light soils, but fifty-six pounds per pole will not be too much on heavy land, and the dressing should be given either six or eighteen months before a Cabbage or Turnip crop is sown; the longer period is the more certain in its effect. Preference should be given to stone or rock lime over chalk lime. The former is much more powerful and efficient. It may be necessary to repeat the dressing twelve months after the first application. As regards the occurrence of Anbury in seed-beds, frequent transplantation is a very effectual mode of stopping its progress, for the little galls can be pinched off by the workman, and burned as he proceeds; and the plant, being invigorated by change of soil, will soon grow away from the affection. In transplanting Cabbages it is a good plan to discard and burn such plants as are obviously affected with Anbury. It is worthy of remark that in market-gardens this disease is by no means so prevalent as to interfere with the routine of cultivation, although the Cabbages, Broccoli, and Cauliflowers grown in these grounds are, under other circumstances, especially liable to attack. By 'other circumstances' we mean that market-gardens are generally kept under high cultivation, the land being perpetually turned and heavily manured; and these measures appear to be a preventive of Anbury, while they result in heavy crops. But on land less energetically tilled Anbury may prevail to such an extent as to interfere seriously with the order of cropping. Another very important mode of keeping down the pest consists in burning instead of burying the stumps and all other refuse of the crop that cannot be turned to account. Confusion may be prevented if we point out that Club-root, Anbury, or Finger-and-toe--whichever name may be used--is quite distinct from an apparently similar malformation of the root which is sometimes induced by certain characteristics of soil, seed, or manure, and is in fact a case of reversion to the original wild type. Instead of a shapely, solid Turnip, the bulb is divided into a number of coarse, worthless tap-roots, caused by either poverty of the soil, careless cultivation, or a degenerated stock of seed. Those who save their own seed continuously for years are almost certain to become well acquainted with this malady. They will find a change of seed necessary, and at the same time an alteration in the routine of culture. A healthy, vigorous plant, derived from a pure seed-stock, does not easily make Finger-and-toe, but a sound root that stands for food and money. 'Grub.'--The wart-like growths formed upon the roots of Turnip and Cabbage by the little hard beetle known as the Turnip-gall Weevil, Ceutorhynchus pleurostigma, are also quite distinct from Finger-and-toe. By cutting across a malformed root of Turnip or Cabbage it is usually not difficult to determine the cause of the mischief. If it is Finger-and-toe the root will be found filled with decaying matter; in the case of Weevil attack the small legless maggots, commonly called 'Grub,' will be brought into view; and if it is merely an instance of reversion the cut root will appear to be healthy. Potato Disease.--The fungus which causes the Potato Disease, or 'Blight' as it is sometimes called, was formerly known as Peronospora infestans; now it is recognised by scientific authorities as Phytophthora infestans. The mark of its pestilent touch on the foliage, and its destructive effect on the tubers, are unfortunately too familiar in gardens and on farms. In dry seasons its energies are restricted, but the scourge is never absent, and during wet summers the parasite may do its deadly work on such a vast scale as to cause a Potato famine. Moisture is a necessity of its existence, and in rotting haulm, decayed tubers, and damp soil the spores remain in a resting condition until they are afforded an opportunity of multiplying with the marvellous rapidity that invests the disease with its terrible power. A series of six illustrations, five of which are highly magnified, will enable the reader to follow the development of Phytophthora infestans.[1] [Illustration: No. 1] The illustration No. 1 shows a Potato leaf on a reduced scale disfigured by the attack of the fungus. The Phytophthora is sending mycelial threads (called hyphae) in all directions through the substance of the leaf, feeding on the protoplasm of the cells and destroying the chlorophyll, or leaf-green, in those cells. [Illustration: No. 2] [Illustration: No. 3] No. 2 shows the fungal threads at work. In a diseased Potato plant these threads, or mycelial hyphae, make their way through the substance of the leaves, and down the haulm into the tubers, from which they consume the food stored there. No. 3 exhibits the various stages of germination of one of the conidia of Phytophthora infestans: (a) the ripe conidium in water; (b) protoplasmic contents breaking up into blocks, which separate and escape (c and d) as minute kidney-shaped zoospores (e) each with two cilia; (f and g) the zoospore coming to rest and losing its cilia; (h, i, j, and k) successive stages of germination of the zoospore. [Illustration: No. 4] No. 4 represents a longitudinal section of Potato-stalk with germinating zoospore, the germ-tube of which has pierced the cell-wall, and is growing inside the cell, as shown at +. [Illustration: No. 5] [Illustration: No. 6] No. 5 affords a view of another piece of tissue of the stem of a Potato plant, and shows the hyphae of Phytophthora infestans running in the cell-walls; (a) nucleus of a cell; the other contents shown are crystals and chlorophyll corpuscles. No. 6 is a section of a Potato tuber: A, the cell-walls; B, the starch grains; C, the mycelial hyphae. Spraying Potato plants twice or thrice with Bordeaux mixture has proved effective in warding off the attack of Phytophthora infestans, and the practice is now freely adopted, especially in humid districts. The first application should be given towards the end of June or early in July, immediately the haulm is sufficiently developed. The Bordeaux mixture is made in the proportion of four pounds of pure copper sulphate and two pounds of quicklime to forty gallons of water. The foregoing quantities will give what is known as the one per cent. mixture. For the two per cent. mixture the quantities of copper sulphate and quicklime must be doubled, but the amount of water should remain at forty gallons. In its effect on the fungus, however, little difference is to be found between the two solutions. The copper sulphate is stirred into a few gallons of hot water placed in a wooden tub or earthenware vessel. When quite dissolved, add twenty or thirty gallons of cold water. The lime, which must be freshly burnt quicklime, is then slaked in another vessel and thoroughly stirred with two or three gallons of water until it is of the consistency of thin cream. As soon as the liquid is quite cold, filter it through coarse sacking into the copper sulphate solution and add water to make a total of forty gallons. To be effective, Bordeaux mixture must be applied in the form of a fine spray, and not with a coarse-holed syringe. The Burgundy mixture, the use of which is preferred by some, acts in a very similar manner to the Bordeaux mixture, and is made in the same way as the latter, except that washing soda (five pounds) is substituted for quicklime. Those who leave Potatoes to rot in the ground because the crop is not worth digging, or who bury diseased haulm and tubers in a shallow trench, under the impression that it is a safe way of getting rid of worthless vegetation, are simply storing Phytophthora for another attack in the event of Potatoes being planted in the same land again. If buried at all, it must be at a considerable depth, but the effectual method is to destroy all Potato refuse by fire. Wart Disease (Black Scab) of Potatoes (Synchytrium endobioticum, Percival).--This extremely infectious and destructive disease of the Potato has been given a variety of names in different parts of the country, but it is now generally known as the Wart or Cauliflower Disease, the latter term being attributable to the Cauliflower-like appearance of the outgrowth of the fungus. This outgrowth first shows in the eyes of the young Potato in the form of small wrinkled warts. These multiply and combine, thus creating a dark spongy scab which eventually decomposes. Where the disease is very rife it attacks haulm as well as tubers, and a yellowish-green mass may sometimes be found just above or just below the surface of the soil. As a rule, however, no outward indication of its existence is to be seen in the crop during the early stages of growth, but towards the end of the season the haulm of badly diseased plants often retains a fresh green appearance when the foliage of others, which are healthy or only slightly attacked, is dying off. Infection is perhaps most commonly spread by the planting of diseased tubers. Another frequent means of dissemination is caused by consigning infected haulm to the waste heap instead of to the fire. The spores may also be introduced in manure from animals fed on diseased Potatoes in a raw state, and they may even be carried from one plot to another on garden implements or the boots of those who walk across infected ground. Immediately any sign of the disease is observed it should be dealt with promptly and in no uncertain manner. Every particle of the infected material must be carefully collected and burned. Dig out the soil around all diseased plants and burn this also. On infected land it is important that some crop other than Potatoes be taken in the season following the outbreak, and, if possible, such land should not be used for Potatoes for at least five or six years. But where garden space is limited, a contaminated plot may have to be requisitioned for Potatoes within two or three years. In such cases it is an excellent plan to dust the sets freely with sulphur at the time of planting and to repeat the application before earthing up. Although for some years the unremitting labour of experts has been devoted to the investigation of Wart Disease, and innumerable experiments have been undertaken, no effectual remedy has yet been discovered. It has been found, however, that certain Potatoes are resistant to the disease, and by order of the Ministry of Agriculture and Fisheries none but 'immune' varieties may be planted in districts scheduled as infected areas. A notification of the existence of Wart Disease must be made to the Ministry immediately it is observed. Leaf Spot of Celery.--This disease, which is caused by a minute fungus (Septoria apii, Chester), is capable of inflicting serious damage to the Celery crop unless prompt measures are taken to exterminate it. The first sign of its appearance is to be found in the leaves in the form of small brown patches. These are, however, quite distinct from the spots deficient of leaf-green due to the attack of the Celery Fly larvae, and on close examination may be recognised by the presence of a number of very small black points. From the leaves the fungus quickly spreads over the leaf-stalks and finally to the heart of the plant, ending in its total collapse. So rapid is the multiplication of the spores, especially in moist weather, that a few diseased plants are capable of infecting a large plot within two or three weeks. Immediately discoloration of a leaf is noticed the affected portion of the plant should be picked off. If the stage of the disease is so far advanced that the outer leaf-stalks have become decayed, the entire plant should be removed and destroyed. It is of the utmost importance that every particle of diseased material be consigned to the fire and not to the waste heap. Spraying three or four times with Bordeaux mixture at intervals of two or three weeks may be helpful in the case of a light attack, but the safest course always is to remove and destroy any plant on which the fungus is found. One of the most frequent means of introducing Leaf Spot of Celery is through the use of infected seed, and therefore only seed which has been treated for the destruction of the fungus should be sown. Lettuce Mildew.--This fungus is named Bremia lactucae, formerly known as Peronospora ganglioniformis, and is sometimes of the most destructive character. It covers Lettuce leaves with a fine white bloom, which decomposes the leaves, and makes them adhere together in one putrescent mass. It should be looked for in its earliest stages, and be hand-picked and burned. Old Lettuce stumps should likewise be pulled and burned, otherwise they may harbour the disease. Onion Mildew is caused by the fungus Peronospora Schleideni, which is occasionally disastrous in its effects, more especially in cold, wet seasons. It occurs at uncertain intervals of time with extraordinary virulence, and then utterly destroys the crops. Autumn sowing is considered a good preventive by many growers, as the disease is frequently fatal to spring seedlings. In its early stages the mildew may be successfully dealt with by freely dusting the plants with flowers of sulphur when wet with dew, or by the application of sulphide of potassium in the proportion of one ounce to a gallon of water. Otherwise all diseased material should be removed and burned. Pea Disease.--Although garden Peas often suffer badly from the attacks of Peronospora viciae, which is the cause of Pea Mould, yet the most deadly foe to Peas, especially late Peas, is a fungus of a totally different character. To such an extent does the Pea Blight sometimes devastate the later Peas, particularly in dry summers, that the whole crop is in some gardens completely annihilated. The name of the fungus of the Pea Blight or Mildew is Erysiphe Martii. Its attack is often made suddenly; the leaves then lose their natural green colour, and become yellowish and densely coated with a fine white bloom; this bloom becomes at length dusted over with innumerable minute black bodies, which look, under a lens, like tiny spiders'-eggs in the web. These little black bodies are filled with extremely small transparent vessels, and each vessel contains from four to eight spores or seeds. Our illustration shows this Erysiphe enlarged one hundred diameters, with two of the vessels containing the spores removed from the globular spots and further enlarged. The only safe way of dealing with infested Pea plants is to burn them. Many other species of fungi belonging to the same genus attack fruit trees, vegetables, and garden flowers. It is, however, unnecessary to illustrate them, as they more or less resemble the fungus of Pea Blight. They all arise from an Oidium condition, similar to the Oidium or Mildew of the Vine, and it is in this condition alone, as in the case of the Vine, that they can be reached by any fungicide. [Illustration: X.100. FUNGUS OF PEA MILDEW Erysiphe Martii] Tomato Diseases.--The Tomato, like its near relative, the Potato, is subject to a number of destructive diseases which spread rapidly if allowed to become established. The most serious of these epidemics are found among crops cultivated under glass, where the forcing treatment which they often receive, and the soil and atmospheric conditions, render the plants abnormally susceptible to the attacks of fungi and insect pests. Perhaps the most virulent forms of disease with which the Tomato-grower is troubled arise from the attacks of parasitic fungi and bacteria, among which the following are most frequently met with:-- SLEEPY DISEASE, or TOMATO WILT.--In its outward symptoms and effects this disease somewhat resembles an attack of Root-knot Eelworm, but the swellings are absent from the root. The plants for a time appear quite vigorous and healthy, but when full-grown they suddenly wilt and die within a few days. The malady is caused by the fungus Fusarium lycopersici, which first invades the roots and ultimately eats its way through the substance of the collar or stem near the surface of the soil, in consequence of which the supply of water taken up by the roots is cut off from the leaves above ground and the plant collapses. There is no remedy for the Sleepy Disease of Tomato, and plants which bear evidence of infection should be carefully dug up and burned. TOMATO 'STRIPE.'--This disease of the Tomato is comparatively common, and although the attacks are sometimes slight its ravages may be disastrous when conditions are favourable for its development. The presence of Tomato Stripe is usually first noticed about the time fruit is forming. The stems of the diseased plants then exhibit dark spots and elongated sunken stripes of a brown tint, and yellow patches, which turn brown later, appear on the leaves. Brown pits or depressions develop on the fruits and spoil their appearance. The disease has been traced to the action of a bacterium which closely resembles, or is identical with, that causing Stripe among Sweet Peas. This organism probably resides in the soil, and the signs of its attack are often visible in young plants. In severe cases the soil of the house should be removed and replaced with fresh loam. But when only slight traces of the disease are apparent, partial sterilisation of the soil by means of carbolic acid, as recommended for Root-knot Eelworm on page 425, may be adopted. One of the surest means of guarding against losses by Stripe disease, is to promote robust healthy growth, and to avoid extreme forcing conditions, particularly by the excessive use of nitrogenous manures. Where, however, forcing manures may have been employed in too large a quantity, an application of potash (in the form of kainit or sulphate of potash) and phosphatic fertilisers should be given to counteract the effect of the nitrogen. Immediately any trace of the disease is found, remove the affected part of the plant, if it is possible to do so without serious injury, but otherwise the entire plant should be uprooted and destroyed by fire. It should be remembered that the organism can be carried on the fingers and on tools, and therefore knives with which affected plants have been trimmed should be sterilised with lysol or some other antiseptic solution before being used on healthy plants. TOMATO-LEAF RUST.--The leaves of the plant attacked by this disease rapidly become covered with a dull brownish velvety mould, or fungus, known as Cladosporium fulvum. From the mouldy spots and patches thousands of spores are readily carried by a slight current of air to the surrounding healthy crop, and unless prompt measures are taken to check the pest the whole house is rapidly involved. Excessive atmospheric moisture encourages the mould, and it is spread extensively if diseased plants are sprayed with water in the presence of healthy ones. Judicious management in air-giving, which is one of the fundamental principles of successful Tomato culture, will do much to prevent the attack of Cladosporium fulvum. Under regular examination the presence of the disease will be revealed before considerable damage can be inflicted, and when only a few leaves are affected, carefully remove and consign them to the fire. Spraying with the Bordeaux mixture at half the usual strength is recommended when the disease is first noticed. When the plants are bearing flowers or fruit, fungicides containing copper must not be used, but a solution of liver of sulphur, one ounce dissolved in six gallons of water, employed instead. ROOT-KNOT EELWORM.--A dangerous insect pest which frequently attacks the Tomato, in common with the Cucumber and Melon, is the Root-knot Eelworm (Heterodera radicicola). The root on which the swollen pea-like knots develop do not carry on their ordinary functions, and the leaves droop, the stem becomes limp, and the whole plant soon collapses and dies if the trouble is severe. The treatment suggested on page 425 should be adopted. Sometimes the outdoor Tomato crop is attacked by Phytophthora infestans, the fungus responsible for the Potato Disease: Bordeaux mixture should be used to check it. Directions for preparing the Bordeaux mixture are given on page 440. Another useful preparation which checks many fungus diseases may be made by dissolving one ounce of potassium sulphide (liver of sulphur) in three or four gallons of water, to which should be added an ounce or two of soft soap. The last named greatly assists in the complete and uniform wetting of all parts of the foliage.

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