The Culture Of Vegetables And Flowers From Seeds And Roots Part 48

ROOT-KNOT EELWORM.--A dangerous insect pest which frequently attacks the Tomato, in common with the Cuc.u.mber 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 pota.s.sium 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 a.s.sists in the complete and uniform wetting of all parts of the foliage.

THE FUNGUS PESTS OF CERTAIN FLOWERS

==Cineraria and Senecio Disease.==--=Senecio pulcher=, soon after its introduction into England, was attacked, and in some gardens completely destroyed, by a fungus named =Puccinia glomerata=, or rather the =Uredo= stage of this fungus with simple, not compound, spores. The fungus is well known, being closely allied to that which causes the rust or mildew of corn crops. It is very common on the wild species of Groundsel in England, being especially frequent and virulent on the Ragwort Groundsel, =Senecio Jacobea=, from August to October. The leaves of infected plants are covered with rust-coloured dusty pustules, the =Uredo= condition of the fungus, and known in this stage as =Uredo senecionis=, sometimes termed =Trichobasis senecionis=. The fungus has a =Puccinia= stage of growth very similar to that of the Hollyhock fungus, =Puccinia malvacearum=.

[Ill.u.s.tration: FUNGUS OF SENECIO DISEASE =Uredo senecionis=]

At A is ill.u.s.trated a fragment of a leaf of =Senecio pulcher=, natural size, and covered with the orange-coloured fungus; at B a small part of a =Uredo= pustule as seen bursting through the cuticle of the Senecio leaf.

No remedial measures for the extirpation of this fungus are known, but as garden Senecios and Cinerarias are infected by diseased plants of Wild Groundsel, it is desirable that plants of the latter (especially when diseased) should be destroyed. Weeds in and about gardens are a common cause of disease in cultivated plants. It often happens that a weed, being st.u.r.dy, is only slightly inconvenienced when attacked, whilst a cultivated plant will speedily succ.u.mb if attacked by the same fungus. This is the case in the =Sempervivum= disease. In this country the common House Leek is the nurse-plant, and is seldom much injured; but if the disease =Endophyllum sempervivi= gets among greenhouse species, every plant may be utterly destroyed.

[Ill.u.s.tration: FUNGI OF GLADIOLI, LILIES, ETC. =Urocystis gladioli= and =Ovularia elliptica=]

==Gladiolus, Crocus, Narcissus==, and ==Lily Diseases.==--In certain soils and situations where the ground is heavy and the atmosphere inclined to be humid the Gladiolus is very subject to a destructive fungoid disease.

This is especially the case during unusually wet summers. The disease attacks the corm, and corrodes and decomposes the tissues, so that on cutting open a corm the whole interior, or such parts as are diseased, will be found permeated with a deep, foxy colour. It is believed by some persons that one stage of this disease is identical with the disease named 'Tacon' by the French, and in this country known as 'Copper Web,'

=Rhizoctonia crocorum=. This =Rhizoctonia= is a mere sp.a.w.n or mycelium, a ma.s.s of rusty-brown material like a thick coating of spider's web of a red tint. This parasite attacks the Crocus (especially =C. sativus=), the Narcissus, Asparagus, Potato, and other plants. Immersed in the softer and damper portions of the red substance of the corm may frequently be found great numbers of large compound spores, as ill.u.s.trated at A (enlarged two hundred and fifty diameters). These bodies belong to the fungus named =Urocystis gladioli=; but whether they really belong to the sp.a.w.n named =Rhizoctonia= there is no conclusive evidence, as the spores have never been seen on the threads or upon any sp.a.w.n. The spores are very ornamental objects, consisting of from three to six compacted inner brown bodies, surrounded by an indefinite number of transparent cells. At maturity these spores break up as at B, and are the means of reproducing the fungus.

The Colchic.u.m is attacked by a closely allied but different species of =Urocystis=--viz. =U. colchici=. The Ranunculaceae are attacked by another ally in =U. pompholyG.o.des= and Rye is attacked by a third in =U.

occulta=. No method of cure has yet been published for this pest; it is, however, desirable that only sound and good corms should be planted, for if infected corms are placed in the ground it is one certain means of propagating the disease. The bars shown across the ill.u.s.tration of this disease are magnificent crystals, very common in Gladiolus corms.

Lilies are very subject to a disease in early summer: the leaves get spotted and damp, and rot off; the flower buds speedily follow, and leave the bare stalk. The disease of Lilies is caused by a fungus closely allied to the fungus of the Potato disease, and named =Ovularia elliptica=, known also as =Botrytis elliptica= (see ill.u.s.tration C). The spores are large, and produce zoospores, or spores with hair-like tails (cilia), capable of swimming about in water or upon moist places. This pest attacks a large number of species of =Lilium=, both before and after flowering. =Hyacinthus candicans= and some Tulips suffer from a very similar, if not the same, organism. This fungus has been described as a true =Peronospora=. Bulbs are subject to many fungus growths as =Volutella hyacinthorum=, =Didymium Sowerbei=, &c.; many fungi follow the decay of the bulb, others undoubtedly produce or greatly accelerate decay. No remedy is known, but we advise the purchase of the soundest and best bulbs. Good drainage and sufficient air are indispensable. All infected foliage and stems should be burned.

==Disease of Hollyhocks and Malvaceous Plants.==--In some parts of England the cultivation of the Hollyhock had at one time quite ceased owing to the attacks of a microscopic fungus named =Puccinia malvacearum=. In gardens and nurseries, where years ago Hollyhocks were one of the chief ornaments of the place, it became impossible to grow a single plant. The disease is not confined to the Hollyhock, for it attacks many malvaceous plants, notably the Mallows of our hedgesides. We have seen plants of the white variety of the Musk Mallow (=Malva moschata=) totally destroyed by this parasite. The home of the Hollyhock fungus is Chili, whence the Potato fungus reached us. The Hollyhock fungus first attacked the malvaceous plants of Australia, and then reached England in 1873 by the continent of Europe. The best and cleanest seeds of the Hollyhock should be purchased.

[Ill.u.s.tration: FUNGUS OF HOLLYHOCK DISEASE =Puccinia malvacearum=]

A fragment of a Hollyhock leaf is ill.u.s.trated at A, dotted with the characteristic brown pustules; these pustules cover the stems as well as the leaves. At B is shown the edge of a pustule enlarged one hundred diameters and seen in section; to show the whole of a pustule in section from six inches to a foot of s.p.a.ce would be required. Bursting through the skin of the plant may be seen a dense forest of threads, each thread bearing a spore with a joint across the middle. One pustule alone will produce thousands of these double spores. At C some of the threads and spores are still further enlarged to two hundred diameters, and at D one ripe spore is shown falling from the thread and breaking asunder--each piece is a reproductive body or spore. When mature, these minute spores or 'seeds' are carried in the air by millions. At E one of the compound spores is enlarged to four hundred diameters. As this disease is seated within the tissues of the plant, remedies are difficult of application, and in many cases attempts at cure have failed. No doubt the fungus is nursed by malvaceous weeds. Infected Hollyhock plants and allied weeds should be destroyed by fire or by deep burying.

==Poppy Disease.==--Garden Poppies are often attacked by a fungus pest closely allied to the fungus of the Potato disease, and named =Peronospora arborescens=. It grows sometimes in abundance on the common Red Poppy of cornfields (=Papaver Rhoeas=), and it badly attacks =P.

somniferum= and all its garden varieties. The fungus grows within the leaves, and emerges with a tree-like growth through the organs of transpiration (the stomates) on the under side of the leaves. Like the fungus of the Potato disease, it speedily sets up decomposition, and destroys the host-plant.

[Ill.u.s.tration: FUNGUS OF POPPY DISEASE

=Peronospora arborescens=]

At A is ill.u.s.trated one of the stems of the Poppy =Peronospora= emerging from the leaf, enlarged seventy-five diameters. The fungus of the Poppy is very much more branched than that of the Potato, and every minute branchlet carries a spore. To save confusion, a large number of spores are omitted from the branchlets in the ill.u.s.tration, and the branches growing from the stem both before and behind are for the same reason left out. At B a tip of a single branch is shown further enlarged to four hundred diameters. The spores in the Poppy fungus are unusually large and numerous: an infected plant will throw off many millions of such spores. All the putrefactive sp.a.w.n of this fungus is inside the host-plant; cure, therefore, is difficult. This disease, like every other plant disease, is always at its worst in ill-kept places where red field Poppies are abundant. Field Poppies are often sown with unclean corn. As prevention is better than cure, all we can advise is, buy the best and cleanest garden and field seeds, cultivate in the best way, and look out for and burn, or deeply bury as soon as detected, all disease-stricken plants, whether wild or cultivated. When diseased plants of any sort are left to decay on the refuse-heap, it is the most certain way of propagating a plant disease for the next year.

==Diseases of Violets.==--Violets are subject to fungoid diseases, both in spring and autumn. The disease of autumn is caused by the brown =Puccinia violae=, allied to the =P. graminis= of Corn and to the =P.

malvacearum= of Hollyhocks and various malvaceous plants. The =Puccinia= of Violets has its yellowish or orange-coloured stage; it is then known as =Trichobasis=, or =Uredo violarum=. In spring and early summer Violets are often badly affected by a fungus named =aecidium violae=, which is apparently identical, however, with =Puccinia violae=. This disease attacks leaves, stems, and sepals, and it is best examined on the leaves. In this position it is seen to consist of a considerable number of minute yellow pustules, each pustule less in size than a pin's head, and all congregated into one flat circular ma.s.s of about a quarter of an inch in diameter. This pest is very frequent on the Dog Violet, but it is perhaps equally common on the Sweet Violets of our gardens in early spring, and it not infrequently spreads to other species of =Viola=. One of the most destructive pests of Violas is found in =aecidium depauperans=, so called because its effect is first to starve and attenuate, and then to totally destroy, plants of =Viola cornuta=. It is a close ally of =Ae. violae=, but it differs in having its minute cups or pustules irregularly distributed all over the green parts of the host-plant instead of being congregated in circular patches, as in =Ae. violae=. Our ill.u.s.tration shows, at A, a small portion of the stem of =Viola cornuta= attacked by =aecidium depauperans=. The minute pustules are seen (natural size) distributed all over the stem, leaf-stalks, and ruined leaves; the effect of the fungus growth is to decompose the tissues of the plant. At B, a transverse section through the stem is ill.u.s.trated and magnified twenty diameters. The section cuts through several of the abscess-like pustules, and it is seen how completely embedded they are in the flesh of the plant. At C, a pustule is seen in section, enlarged sixty diameters to show more clearly the innumerable spores, or 'seeds,'

disposed in necklace-like fashion, which are destined to reproduce the pest in future seasons. Another disease of Violets in autumn is caused by a fungus named =Urocystis violae=. This fungus causes gouty swellings to form on the stalks and princ.i.p.al veins. These swellings at length burst, exhibit black patches, and discharge sooty spores. The fungoid disease named =Phyllosticta violae= is frequently common on Violet leaves in June. In this the spots are whitish. No cure is known, and it is always well to burn or deeply bury all infected leaves or plants.

[Ill.u.s.tration: VIOLET DISEASE =aecidium depauperans=]