February 17, 1912.] 



THE GARDENERS' CHRONICLE. 



101 



Among the best known species, beside L. bulla- 

 tum, are L. scoparium, L. lanigerum, and L. 



Symptoms of the Disease in Orchids. 



results of all, both in arresting the disease and 



flaveseens. All of these jire generally grown in species of Cypripedium, of which abundant mate- 

 rial was sent to Kew r , and it was stated to be 



" I have only observed the disease on cultivated i n the rapid and vigorous growth cf the seedlings. 



the open in Devon and Cornwall and the South 

 of Ireland. L. scoparium shows, in its native 

 country, considerable variation. A plant w r as dis- 

 covered in the South Island of New Zealand, 

 bearing flowers of a bright rose colour. 

 This was named L. Chapmannii, and it has been 



present on most of the plants occupying a large 

 house. The roots are attacked first, then the 

 bases cf the leaves, which gradually become 

 brown, and finally assume the condition of a soft 

 rot, when the who la plant falls over. The snow- 



found that it produces itself fairly true from white Milowia fruit was produced in abundance 



This result is partly due to the absence cf humus, 

 which favours the continuous growth of the 

 fungus in soil containing organic matter, and also 

 to the physical conditions of such soil. 



" The author suggests the use cf coal ashes, 

 volcanic scoria, or naturally or artificially-pow- 

 dered volcanic rocks, as suitable for the formation, 

 of seed-beds." 



seed. Later, a remarkable individual plant was 

 discovered growing in the sand-hills a little north 



w r hen the decayed portions were placed under 

 favourable conditions for its growth. It w r as in 

 of Christchurch, rather over 200 miles distant all probability the spores of this condition of the 

 from where L. Chapmannii had been found, and fungus that spread the disease from one plant to 

 this bore blood-red flowers. This plant is now another in the house, the minute sports being dis- 



known as L. scoparium var. Nichollii. Its foliage 

 is much daiker than that of the type, being 

 of a Copper Beech colour. It is easily propa- 

 gated by cuttings, and will doubtless soon be in 

 commerce. Wyndham Fitzherbert. 



persed by wind, syringing, &c. 



Preventive Methods. 



"It is practically impossible to cur-2 a plant 

 that is once infected, as the mycelium is located 

 in the living tissues of the root, and no substance 



CYANIDE FUMIGATION. 



Fumigation with hydrocyanic acid, though 



largely practised in America, does not seem to 

 appeal much to gardeners en this side of the 

 Atlantic. The reasons are not far to seek, for 

 the fumigants commonlv used are verv effica- 

 cious, and cyaniding has some disadvantages: 

 in fact, its chief recommendation is its extrpmp. 



SWEET PEA STREAK DISEASE. 



The current issue of the Kew Bulletin* con- 

 tains an illustrated article by Mr. George 

 Massie on " A Disease of Sweet Peas, Asters and 



Other Plants. " The article, from which the sp0 res on Peas or other seeds is forthcoming, and 

 following is an extract, attributes streak dis- would not be expected to occur, when it is re- 

 membered that the fungus, as a parasite, con- 

 fines itself to the root and collar of the stem. 

 Infection of the soil may be brought about by 



various means. When a diseased croo is grown, 

 "In those instances where the land is badly the roots in most i nstances become 'thoroughly 



xxi i*n^ living i/ioou^o vx tuc xwu, a^u nv ouucianv^ i TT '1 l l 



is known that will check or kill such mycelium, c ^apness. Until recently the amounts given for 

 without at the same time killing or materially in- ordmar y greenhouse fumigation were far in ex- 

 juring the host-plant. Hence the only means of 

 checking the onslaught of the fungus is by the 

 adoption of preventive measures. The great 

 majority of the disease is obviously due to in- 

 fected land. No evidence of the presence of 



ease of Sweet Peas to the fungus Thielavia basi- 

 color. 



Symptoms of the Disease in Sweet Peas. 



infected, the majority of the Peas do not appear 

 above ground at all. This occurs when both the 

 plumule and radicle are attacked. In such cases 

 if a number cf the Peas are dug up and placed 

 with sterilised manure in a Petri dish, the con- 



decayed, and too friable to remove even if an 

 attempt was made to do so. It is on such de- 

 cayed roots that the Torula or resting-spore stage 

 of the fungus grow r s, consequently the soil be- 

 comes infected, and even if a crop of some kind is 



cess of what is necessary, and two extremely im- 

 portant factors, the time of day and the duration, 

 were apt to be ignored. A fumigation which will, 

 if done in the daytime, blacken and scorch half 

 the plants in a house, will, if done at night, have 

 no ill-effects on them. Whether this be due to 

 the closing of the stomata at night or to some 

 deeper cause is not known. A strong dose of, say,, 

 one ounce of sodium cyanide to every thousand 

 cubic feet, will kill aphis in 20 minutes ; there is, 

 therefore, no point in prolonging the opera- 

 tion. Experiments at the John Innes Horti- 

 cultural Institution showed that a fumigation 

 of ^ ounce of sodium cyanide to every thousand 

 cubic feet for half an hour is quite sufficient to 

 kill all green fly, and even such delicate vegeta- 

 tion as the young fronds of Maidenhair Ferns 



teats kept moist and at a temperature of about afte rwards grown that the fungus cannot attack, was unharmed when tne fumigations were done 

 65° P., the white Milowia condition cf the fungus it finds host . p i ants in the varicus kinds o£ weeds at ni hfc Jtg cogt ig aboufc one . third that of ,, n 

 will appear on the surface of the manure withm growing along with the crop In addition> when ^^ fumi Uon Qnit volume A 



a few days. ^ In the majority of cases the rcot ifc is remembe red that the fungus can pass through ter cf an ounce per thousand cubic feet in 30 



minutes killed 75 per cent, of the " fly," and in 

 an hour killed all but one or two. There is 

 little doubt, therefore, that in an hour and a 



only is attacked, at least at first, and the plant its comp i Gte course cf devclonment as a pure 



often attains a considerable growth before any 



sign of injury appears, but suddenly the plant 



may begin to wilt, turn yellow, and die, or in 



some instances only one branch dies, the rest cf 



the plant remaining green for some time, but 



rarely producing perfect fruit. Another very 



common symptom of the disease is known to 



growers of Sweet Peas under the name of 



" streak " or M stripe," characterised by the pre- 

 sence of dingy yellow streaks or stripes on the 

 leaves and stem. This condition is the result of 

 what may be termed a mild attack, the fun us not 

 being present in the tissues of the root and collar 

 in sufficient quantity to kill the plant outright, 

 yet sufficiently abundant to prevent the root from 



saprophyte, feeding on the humus present in the 

 soil, it will be readily understood that when land 

 is once infected, the fungus is quite capable of 

 holding its ground, and cf quickly extending its 

 area of devastation, unless prompt measures are 

 taken. The infection of a new area is, in the 

 majority of instances, dus to the use cf manure, 

 on which material the fungus flourishes and re- 

 produces itself at a rapid rate. 



V Commercial formalin (= 40 per cent, for- 

 maldehyde), has proved to be the most effective 

 fungicide for sterilising infected soil. In the 



half all w T ould have been killed. 



On the other hand, five ounces for three hours 

 failed to kill red spider, and injured the 

 plants. One ounce for half an hour is said to 

 kill "mealy bug." The method of procedure is 

 very simple. A weight of strong sulphuric rather 



in excess of the weight of sodium cyanide to 

 be used is poured into an earthenware receptacle 

 containing about twice this weight of water, and 



M<11 . • ... ,. , ,- . , lings, the soil of the seed-beds is thoroughly 



performing its function to the fullest extent hence i j uu i +• *t r - + • ^ 



f. . ° ,, _ , c luiie&t cAient, iience soa ked with a solution cf tormahn in water, in tne 



the stem and leaves lack water and are hungered. 

 The green portions of a plant showing " streak * 

 correspond to the position occupied by the vas- 

 cular bundles or water-conveying vessels where 

 the limited supply of water obtained by the root 

 makes itself evident, whereas the yellow portions 

 between the veins are dead, owing to lack of 

 water. If the root of a Pea plant that has been 

 attacked by the fungus is examined, it will be 

 s-2en to present a blackened or charrod appear- 

 ance, and very frequently to be more or less de- 

 cayed on one side, suggesting the idea that it had 

 been gnawed by wireworm. In some cases small 

 black patches of the Torula form of fruit are pre- 

 sent on the surface. 



United States, where Thielavia proves very de- when all is ready, the cyanide, roughly powdered, 

 structive in causing a root ret of Tobacco seed- i s poured in and the door locked. 



There is no point in prolonging the fumigation 



SYMPTOMS OF THE DISEASE IN ASTERS. 



" So far as my experience goes, Asters are 

 always killed outright during the seedling stage. 

 When the plants are about 3 incl s high, they 

 commence to wilt, and soon fall over, as in the 

 disease known as " damping off." The roots of 

 diseased plants are shrivellled and blackened, and 

 all the rootlets are dead. The fungus appears to 

 spread very rapidly in the soil, as whole batches 

 of seedlings collapse simultaneously. 



proportion of one pint of formalin to twelve gal- 

 lons of water. One gallon of the mixture should 

 be allowed for each square foot of surface. After 

 the watering is completed, the soil should be 

 covered for two or three days with coarse sacking 

 or canvas, to keep in the fumes. The watering 

 should be done after all digging has been done 

 and when the seed-beds are in a condition ready 

 for sowing, and a week cr ten days should inter- 

 vene between the scaking of the soil and the 

 sowing of seed, to allow f; r the complete escape 

 of the formaline fumes and the drying of the soil. 



" When green manure is dug into land intended 

 for seed-beds, it shculd previously be thoroughly 

 watered with formalin as above. 



" Professor Benincasa has quite recently con- 

 ducted a series of experiments, as to the best 

 means of checking root-rot of Tobacco in seed- 

 beds. Having proved that infected soil is the 

 usual source of injury, and that heating such soil 

 to a temperature of 90° C. does not completely 

 eradicate the disease, c« niparative tests were 

 made by using ordinary garden soil, pure sand, 

 and volcanic ash or pumice for seed-beds. The 

 plants grown in garden soil were badly infected, 

 seed-beds of sand proved very efficient in con- 



beyond the time necessary to kill insects, as it is 

 only detrimental to the plants : in practice this 

 time is half an hour with half an ounce to the 

 thousand cubic feet, and longer as the charge 



decreases. 



It should be noted that if potassium cyanide 

 is used, nearly double the amount is required, 

 and also more acid in proportion. It is also more 

 expensive. 



A great deal has been said about the danger 

 attending the use of cyanide as a fumigant. As 

 a matter of fact, with reasonable care, there is 

 no danger, but a fumigation of this sort should 

 not be done alone. If care is taken not to inhale 

 the gas, it will do no harm. Plants vary con- 

 siderably in their susceptibility to damage by cya- 

 nide ; some, like Primula sinensis, are very resist- 

 ant, while Roses and Gerberas are extremely 

 susceptible. It can only be found by experiment 

 wdiich can safely be fumigated ; it was found, for 

 instance, that Diplacus glutinosus is very suscep- 

 tible, even to small amounts, its rather glutinous 

 young leaves being scorched in the same way as 

 aie wit leaves. Needless to gay, the drier the house 

 before fumigation the- better, as the gas is ex- 



Kew Bulletin of Miscellaneous Information, No. 1, 1912. trolling the disease, volcanic ash gave the best tremely soluble in water. W. O. Backhouse. 



