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 {~<control>~}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.