Investigation of Diseases of the Rose 
THE investigations covered more or less briefly in 
this report were begun August 1, 1916. During 
the first four months much time was spent in visit- 
ing rose plantings in northeastern United States, makmg 
a survey of diseases. This seemed desirable m order to 
acquaint us with the various diseases, together with their 
range and the extent of injury caused by them in this 
country. With these facts in mind suitable plants and 
materials have been collected for experiments now under 
way which will prove of the greatest value to growers 
of roses. 
The gardens and greenhouses of about fifty rose grow- 
ers have been visited. The number and extent of the 
diseases present have been noted and specimens taken 
for further study. Probably an equal number of grow- 
ers have also materially aided the work by sending in 
specimens. These specimens have been examined and 
the grower advised as to the cause and control of the 
disease so far as our present knowledge and experience 
allow. If the trouble proved to be new, of unusual 
interest or of a serious nature, special work has been 
started to determine the unknown facts regarding the 
disease. 
The survey and correspondence with growers haj 
shown the most important rose diseases in order of im- 
portance to be (1) black spot, (2) mildew, (3) crown 
gall, (4) stem canker, (5) Phyllosticta leaf spot, (6) 
rust, (7) bud rot, (8) other leaf spots. Practically all 
of these diseases are always present and take yearly 
tolls from the growers of surprising magnitude. It is 
not uncommon to find gardens and houses with all the 
plants completely defoliated by ravages of the leaf spot 
diseases, especially black spot, thus making the plants 
unsightly and so reducing their vitality tliat they are 
susceptible to attacks of other fungi, from which roses 
are ordinarily immune, and to frost injury. It is unneces- 
sar\' to mention the damage done by mildew, while there 
is an ever-increasing demand for information relating 
to crown gall, stem canker, rust and bud rot. Unfortu- 
nately, very little is known regarding the control of most 
of these diseases ; and many points remain to be investi- 
gated concerning the control of such common and well- 
known diseases as black spot and mildew. 
A new, and what appears to be one of the most 
important diseases of the rose, has been observed by the 
writer in visits to rose houses. We are calling it the 
"crown canker." Specimens have been sent to the De- 
partment by growers from many parts of eastern United 
States and from as far west as Missouri. It was first 
observed by the writer in September, 1916, but talks 
with growers indicate that the disease has been present 
for possibly four or five years. All varieties seem ti 
be susceptible to the disease. The plant is attacked 
just below the surface of the soil and although the disease 
advances slowly, the death of the plant is sure with an 
ever-decreasing number and quality of flowers. 
This disease, which has never been described, is con- 
sidered of such importance that a large part of the 
writer's time is being devoted to a study of the life 
history of the causal fungus and the development of a 
method of control. Several large growers have stated 
that unless help is obtained they will be forced out of 
business. With the disease already known to be present 
in the houses of ten large growers, it is safe to assume 
that other growers have plants similarly afifected and that 
the disease will be widely distrilnited and increase rapidlv 
ni importance. Steps must be taken immediately to con- 
trol this disease. Not only is it important that' growers 
who already have the disease shall be furnished with 
control methods, but it is even of greater importance 
that the method of dissemination of the fungus be worked 
out in order that the further spread of the disease be 
checked. 
What appear to be other new diseases than the one 
mentioned above have been brought to the writer's 
attention, but too little progress has yet been made in 
this investigation to give definite statements at this time. 
A. Black spot. It is planned to conduct extensive 
experiments for the control of this disease during the 
coming season. Plants at the Cornell Test Garden and 
at Chase Brothers' Nursery, Honeoye Falls, New York, 
will be treated with various fungicides along the lines of 
recent developments in plant disease control. One of 
the most important fungicides to be tried is that of finely 
ground sulphur applied in the form of dust. 
Suitable plants have been obtained and are now grow- 
ing in the greenhouses at Cornell for similar experi- 
ments for the control of black spot under glass. 
P>. Mildew. Experiments for the control of mildew 
through the use of finely ground sulphur used as a dust 
on both indoor and outdoor roses. 
C. Phyllosticta leaf-spot. A study of the life history of 
the causal organism is now being made. This is one 
of the most important leaf-spot diseases of Ramblers, 
and methods of control will be tried during the coming 
season. 
D. Crown gall. Some 200 healthy plants have been 
obtained to be inoculated with bacteria causing this 
disease. These plants will be grown to determine the 
efl^ect of the disease upon the plant, there being a diverg- 
ence of opinion as to just how much damage is done. 
E. The nezv root or crown disease, crown canker. 
Extensive experiments for the control of this disease 
are now under way. It is probable that the fungus lives 
in the soil and that successful treatments will be along 
the line of soil sterilization and the practice of sanitation 
in the houses. However, the effects of chemicals — lime, 
acid-phosphate, sulphur, etc. — upon the fungus, when 
applied to the soil, will be tried. Some 300 rose plants 
have been obtained and are now growing in the green- 
houses at Cornell for these experiments. Much time is 
being spent in working out the life history of the causal 
organism, as such information is essential for a com- 
prehensive study of control methods. 
F. Fungi and bacteria causing other diseases of roses 
are being studied in culture. These organisms have 
been isolated from diseased material obtained from 
growers. Their pathogenicity will be tested and control 
experiments conducted where the organisms prove para^ 
sitic and the importance of the disease warrants such 
action. 
It will be seen from the above statements that while 
there is but little yet to report in the line of results in 
control, still considerable progress has been made and 
the foundation laid for experiments for the control of 
diseases which are of extreme importance to the growers 
of roses. There is every reason to expect that another 
year's work will bring results upon which proved and 
definite advice may be furnished the growers for the 
solution of their rose-disease problems. It is hardly 
necessary to add that it is very essential that the work 
be continued, for should it be dropped at this point, 
the work already done will amount to but little. 
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