Part 48 (1/2)

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.