174 



THE AGRICULTUKAL NEWS. 



May 25, 1912. 



FUNGUS NOTES. 



ROSE MILDEW. 



At this time of the year, mildew i.s very common on rose 

 trees, and may be found in almost every garden. The disease 

 attacks the leaves principally on the underside and causes 

 them to curl up and become distorted. It also attacks the 

 young, growing stems and the flower buds. On the latter it 

 causes crumpling and frequently brown discoloration of the 

 outer petals, while it also reduces the .size of the flower. The 

 fungus causing the trouble appears as a very thin dusty white 

 covering on the surface of the parts attacked. The dusty 

 appearance is due to the production of myriads of .spores that 

 are able to germinate on healthy plants, and thus start the 

 disease on them. 



Some varieties of roses are much more susceptible to 

 mildew than are others, but this fact is of little use in pre- 

 venting the disease from appearing in West Indian gardens, 

 partly because it is not easy to obtain information as to 

 what varieties are comparatively immune and what are not, 

 but mainly because the best roses are often the most suscep- 

 tible, and unless immune varieties can be found with almost 

 identical flowers, the more attractive forms will be planted 

 whether they are immune or not. 



Various measures have been recommended for the control 

 of the disease. One method is to dust the plants with a mix- 

 ture of 2 parts by volume of flowers of sulphur with 1 part of 

 quicklime. Thi.s mixture should be put in a muslin bag 

 and shaken on to the plants in the same manner as that 

 in which cotton plants are dusted with Paris green. 

 The treatment should be repeated about every ten days, until 

 the trees are free from mildew. The powder adheres best 

 when the leaves are slightly damp with dew or from the 

 eft'ects of a light shower. Another method of treatment is 

 to spray or wash the plants with a solution of liver of 

 sulphur, scientifically known as potassium sulphide. This 

 may be made by dissolving 1 oz of liver of sulphur, 

 obtained from a chemist, in 3 gallons (Imperial) of water; 

 this is equivalent to 3f wine gallons such as are used 

 in Barbados A suitable vessel to use is an old kerosene 

 tin that has been thoroughly freed from oil by scrubbing with 

 hot water and sand. Another solution, recommended by 

 Massee, is that consisting of 1 part of sulphuric acid in 1,500 

 parts of water. For practical purpC'ses, there should be 

 obtained from the chemist a solution containing 1 part of 

 strong sulphuric acid and 9 parts of water. One ounce of 

 this mixture .should be added to one Imperial gallon of water 

 contained in a clean wooden tub or in an earthenware dish. 

 Both the liver of sulphur and the sulphuric acid solutions will 

 scorch young leaves, if the mixture is too strong; and the 

 effect of their application should be carefully watched. 



In addition to the two solutions already described, vari- 

 ous proprietary substances are recommended for treating rose 

 mildew, and some of them have been found to give quite 

 satisf.actory results. Directions for preparing these sub- 

 stances for use are as a rule supplied with them. 



The actual application cf solutions of fungicides often 

 presents some difficulty, in a garden. The ordinary garden 

 syringe, even when it is provided with a fine rose nozzle, does 

 not usually give a spray that will adhere well all over 

 leaves with a thin, waxy coating. Either the solution falls 

 as minute, practically spherical drops on the leaves, or if 



the plants are further wetted the liquid runs into big 

 drops which evaporate slowly, leaving a somewhat too con- 

 centrated solution on the leaves in some places and none at 

 all in others. The drops of strong solution scorch the leaves, 

 and on the other parts the disease is not afieoted. In either 

 of the above cases the spraying is of very little use. A method 

 that would probably be found far more satisfactory, and 

 one that is quite practicable on a small scale, is to wipe care- 

 fully each of the diseased parts wdth a soft sponge dipped in 

 disinfecting solution. The leaves should not be made too 

 wet; all that is necessary is to leave a thin, continuous film 

 of liquid over the surface of the aff'ected parts. The applica- 

 tion of liquid disinfectant should be repeated at intervals of 

 about a fortnight, until the trees are free from mildew. 



In addition to applying a fungicide, it is advisable to 

 pick ofi^ and burn all dead leaves, dead buds, flower.s or 

 other parts killed or badly damaged by the disease, and to 

 collect and burn fallen leaves lying beneath the trees. These 

 measures, if carefully carried out, should prevent the fungus 

 from doing any serious damage. 



IMMORTEL CANKER. 



A disease of the immortel {Erythrina wnhrosa), the 

 Bocarie of Trinidad, has been known to exist for some time 

 in St. Lucia, and an account of its symptoms, with suggested 

 remedial measures, was given in the report of the Jlycologist 

 on the Staff of the Department, Mr. F. W. South, B.A., on his 

 recent visit to that Island. This account is as follows: — 



The disease usually starts from a cut surface, as for 

 instance, where a branch has been removed. It spreads fast, 

 and usually kills the tree. Where it is in its early stages, the 

 bark is somewhat split, and covered with a thin, shiny, trans- 

 parent coating, of a yellowish brown colour, probably consist- 

 ing of a dried gummy secretion, while dark red-brown secre- 

 tions of a gummy nature exude through the lenticels. Inside, 

 the bark is rotted, and wet, and reddish brown in colour. 

 Between the wood and the bark, and in the bark itself, are 

 very numerous insects of several kinds. The insects work 

 almost up to the advancing margin of the diseased area, where 

 the bark is only a little darker in colour on the inside than 

 is the adjoining healthy bark. As the disease progresses, the 

 parenchyma of the bark is destroyed, and the brown fibres 

 alone are left. The bark dries and comes away in sheets, 

 exposing the wood. The wood does not appear to be aflfected, 

 except that it is bored by a beetle. The diseased tissues have 

 a strong, characteristic, and very unpleasant smell. 



It would seem that careful excision and burning of the 

 diseased bark, followed by tarring, should control the disease. 

 The excision should be done with a knife that is frequently 

 sterilized, and should extend well into the healthy birk. The 

 exposed surface of the wood should be well fl.uii.xl with 

 a torch, before being tarred. 



A disease of the same species of Erythrina was reported 

 by Carruthers from Ceylon, and he believed that it was due 

 to the same fungus as that causing canker of cacao. At the 

 present time, however, cacao canker is known to be caused 

 by Phytophtliora Faheri, while this fungus has not so far been 

 found to develop from diseased immortel bark in St. Lucia. 

 Moreover, Carruthers believed the immortel disease to be due 

 to a species of Kectria, to which he attributed cacao canker. 

 Inoculations with fungi obtained from the diseased trees in 

 St. Lucia are contemplated, and these may throw some light 

 on the cause of the disease. 



