508 



The Weekly Florists' Review* 



aiAKCH 29, 1900. 



been known for a long time and is 

 quickly recognized by the powdery 

 coat it develops upon the affected 

 parts. It is so rapid in its develop- 

 ment that rose growers are sometimes 

 inclined to assign the cause of the 

 growth to that which is in reality only 

 the condition or conditions favoring 

 the appearance of the mildew. It 

 comes from spores, which, falling 

 upon the surface of the plant, will 

 quickly germinate and produce a cob- 

 webby coating to the foliage. This 

 fungus is so different from the others 

 that have been mentioned that a word 

 is needed in way of explaining the 

 habit of the parasite, as this lies at 

 the foundation of the rational treat- 

 ment of the pest. In the first place, 

 the rose mildew is a surface feeder 

 and only attaches itself to the epi- 

 dermis of the host, through which, by 

 means of small suckers, it derives its 

 nourishment from the deeper seated 

 substance. Being therefore entirely 

 upon the surface, the fine threads of 

 the fungus may grow rapidly and 

 make a mildew patch in a very short 

 time that is easily seen. 



The exact conditions that favor this 

 development of the spores are of 

 course better known to the rose grow- 

 ers than to me. Some of them claim 

 that they can develop the fungus at 

 will by omitting some essential point 

 in heating, warming, or ventilation, 

 particularly the last. If a certain cur- 

 rent of air is sure to produce the mil- 

 dew, and of this I am not fully able 

 to say, it follows that the spores of 

 the mildew were widely scattered 

 through the house and they started 

 into vigorous growth at those places 

 where the conditions were supplied for 

 such activity. 



The superficial nature of the mildew 

 is of great importance when the mat- 

 ter of remedies is considered. It is 

 a fungus that is in the air, as it may 

 be termed, in contrast with most of 

 the rose diseases that when active are 

 deeply seated in the plant. The 

 spores are produced as minute deli- 

 cate cells upon upright filaments that 

 arise from the web of horizontal vege- 

 table hyphae. They are easily reached 

 by fungicides and apparently de- 

 stroyed without difficulty. Any of the 

 ordinary sprays will answer for the 

 mildew, but even these need not be 

 resorted to. provided spraying is un- 

 called for by the presence of other 

 rose fungi. In short, if the mildew is 

 the only enemy at hand, it may be 

 kept in check by the use of flowers of 

 sulphur, either dusted ujjon the plants 

 or even the pipes of the greenhouses, 

 the point being to produce a gentle 

 fumigation of the plants and the 

 whole hou.se with the fumes of the 

 sulphur. Professor Maynard, of the 

 Massachusetts Experiment Station, 

 finds that a small kerosene stove is 

 most convenient for this purpose, and 

 the sulphur, by means of it. is boiled 

 in a kettle for two or three hours 

 twice a week, the house being closed 

 during the operation. The only pre- 

 caution is to use no more heat than 



is sufficient to boil the sulphur, foi; 

 should it catch fire it might damage 

 •the i)larits. 



Mr. .lohn N. May writes that the 

 best way to get rid of the mildew is 

 to close the house about S o'clock in 

 the morning, run the temperature up 

 to 75, then, with a bellows, fill the 

 house full of sulphur. Let the house 

 remain closed till it reaches S.5 or 90, 

 and afterwards let the air in gradu- 

 ally. A constant circulation of air is 

 likewise recommended for roses at all 

 times. Potassium sulphide, one ounce 

 to tv.o gallons of water, sprayed upon 

 the i)lants has proved an effective 

 remedy. Massee states that "flowers 

 of sulphur mixed with about one-third- 

 of its volume of slaked lime dusted 

 on the foliage prevents the spread of 

 the disease." 



Gardeners, from long experience, 

 have come to the belief that rose mil- 

 dew is induced by a weak condition 

 of the plant, resulting from partial 

 starvation, irregular or excessive wat- 

 erin.g, and undue exposure to drafts 

 of cold air. The best success in rose 

 growing, as in all other things, at- 

 tends those who give constant, intel- 

 ligent care to the many details. 



The rose mildew has its close of kin 

 in the mildew of the chrysanthemum, 

 the phlox, pea, gooseberry, grape, 

 cherry, and applQ, and many forest 

 trees, as oaks and chestnuts. Some of 

 them are very injurious, but all can 

 doubtless be controlled by fungicides. 



The Downy Mildew of the Rose. 



(Peroiiospora spar^a Berk.) 



A second form of mildew is some- 

 times troublesome to rose growers. 

 This is a close relative of a similar 

 one upon the greenhouse lettuce, and 

 another is often destructive to spin- 

 ach, while the third is the cause of a 

 soft rot of potatoes. It produces 

 downy or velvety patches upon the 

 leaf, quite unlike the form above de- 

 scril)ed. and the threads run through 

 the substance of the leaf. In this case 

 the fungus will have vegetated for a 

 considerable time before it appears 

 upon the surface, which is entirely for 

 the purpose of producing its multitude 

 of spores borne upon the tips of the 

 many aerial branches. 



It is evident that the sulphur fumes 

 may cause the destruction of the 

 spores, but nuiy not reach the hyphae 

 that are vegetating within the sub- 

 stance of the host. Such treatment, 

 while tending to check the spread by 

 means of the spores, will not be suf- 

 ficient to arrest the growth of the 

 fungus that is already in the tissue 

 of the host. 



There is also a second form of spore 

 that is produced beneath the skin ot 

 the leaf and out of the reach of fun- 

 gicides. As a precaution, it is there- 

 fore well to destroy any mildewed 

 leaves, or else when they fall the 

 spores may he set free. It may be 

 saiil that the careful rose grower will 

 gather >ip and destroy the dead foli- 

 age and reduce as far as possible 



thereby the chances of his plants be- 

 coming diseased from spores that are 

 formed upon or within the old leaves. 



The Rose Rust. 



(Phragnudium subcorlicum Schr.) 



There is a genuine rust of the rose, 

 similar to that of wheat, oats, and 

 other grains, but it is a pleasure to 

 note that it is not common upon in- 

 door roses in this section of the coun- 

 try. It has been sent to me at various 

 times as a troublesome pest upon roses 

 grown for ornament in the flower gar- 

 den and lawn. In "Plant Diseases by 

 Massee." a new book Just published 

 in London, this rust is figured and de- 

 scribed as follows: "A troublesome 

 pest to cultivators of roses, attack- 

 ing more especially hardy hybrid va- 

 rieties. All three forms of the fungus 

 are produced on the same host. The 

 aecidia appear in late spring on the 

 leaves and young shoots, forming 

 powdery, orange patches, and often 

 cause distortion of the shoots. About 

 midsummer the patches become deeper 

 in color, owing to the formation ot 

 uredospores. Finally the teleuto- 

 spores or resting spores are produced 

 as minute black dots on the under 

 surface of the leaves. 



"The appearance of the disease in 

 spring depends entirely on the pres- 

 ence of teleutospores in the neighbor- 

 hood; it is therefore necessary to col- 

 lect and burn all fallen leaves in the 

 autumn. Plants that have been at- 

 tacked the previous season should be 

 thoroughly drenched with a solution 

 of sulphate of copper in water — 2 

 ounces in 3 gallons — in early spring 

 before the buds expand. The soil 

 rotmd the plants may also be sprayed 

 with the same solution. Dilute Bor- 

 deaux mixture, or ammoniated car- 

 bonate of copper solution checks the 

 aecidium and uredo stages. 



"The fungus also grows on wild 

 roses, and these may become a source 

 of infection unless precautions are 

 taken." 



American rose growers are doubt- 

 less familiar with the orange colored 

 powdery masses in early summer 

 which accompany the malformations 

 of stem and leaf, followed by the dark 

 almost coal black patches later in the 

 season. When a shrub is badly in- 

 fested there is little better to do than 

 cut the whole plant away close to the 

 ground. This fungiis is closely re- 

 lated to the one upon the blackberry 

 and raspberry, causing the destructive 

 rust of those plants. It has been 

 shown that the fungous hyphae pene- 

 trate all parts of the blackberry 

 plants even the roots, and the rose 

 grower may not find that severe prun- 

 ing will rid the plant of the pest when 

 it is thoroughly infested. Therefore, 

 as with the raspberry rust, it may 

 be necessary to root out and destroy 

 the rose bush and start again with a 

 healthy plant. This rose rust is a 

 good illustration of the great depth 

 to which a fungus will penetrate in 

 the host and the difficulty of eradi- 



