22 
Journal of Agricultural Research 
Vol. XXIII, No. i 
in the season of the presence of general infection. When sprays were 
finally applied, infection was in many cases already present in the plants. 
Then experimental work in a distant locality compelled the writer to be 
absent from headquarters for several months, so that when he did return 
it was too late to get complete data on the work done. A present con¬ 
sideration of spraying as a control measure for this disease, therefore, is 
more or less theoretical. The erratic occurrence of the disease, because of 
its absolute dependence upon weather conditions, appears to be suffi¬ 
cient justification for publishing what is available on the subject now, 
rather than waiting for the uncertain developments of another season. 
An examination was made in the spring of 1921 of the field in which 
the experimental spraying was done. All plants that were alive were 
well along in their spring growth. It was very evident that a large pro¬ 
portion of the plants had been killed by the disease during the previous 
season. Of a total of 87 plants alive at the beginning of activities in 1920, 
7 had been killed by artificial inoculation. Twenty-five of the remainder 
had been sprayed, and of these only 3 plants, or 13.6 per cent, had died. 
Of the 55 unsprayed plants, 25, or 45.5 per cent, were missing. It is 
certain that many, if not all, of these had succumbed to the disease. 
This would indicate a beneficial effect from the spraying, in spite of the 
fact that infection was present in some of the plants when the spraying 
was done. It gives some ground, therefore, for tentative conclusions in 
regard to the value of spraying. 
Basing conclusions on general information as well as on this experi¬ 
ment, it would seem to be safe to recommend Bordeaux mixture as a 
preventive against infection during the comparatively short period in 
the summer when infection may take place. The spray should be applied 
with some force directly into the crown of the plant, covering the bases 
of the leaf stalks, and leaving a surplus to soak into the crown and the 
ground about it. Its first effect is, of course, lethal to any of the fungus 
with which it comes into immediate contact, at least to any not in thick- 
walled resting condition. There still remains to be determined the effect 
of copper in different concentrations on such thick-walled spores. The 
effect of the spray as a fungicide may last over a considerable period. 
The copper comes into solution gradually; consequently drying merely 
holds it in the very place where it is needed—that is, in the crown of the 
plant—to become available when it is needed during the next wet period. 
The very rain which would normally start the fungus into renewed growth, 
with the production of zoospores, would also still further distribute and 
make effective the fungicide. The distribution of the disease from one 
plant to others in its vicinity, which undoubtedly occurs extensively in 
nature, would also be prevented by an application of Bordeaux. The 
spattering of the water which normally distributes the zoospores of the 
fungus would carry the fungicide with it as well. In the experiments 
referred to the fungicide applied July 12 was persistent a month later, 
despite heavy rains that occurred in the interim. No analysis was made, 
but the abundance of blue stain present indicated that copper was present 
in sufficient abundance to be effective. The staining of the leaf stalks 
would not, under practical conditions, be an objection to the spray, since 
the main harvesting season is over long before the danger season begins. 
No injurious effects whatever have been observed on any of the sprayed 
plants. Caution should be observed not to soak the ground too freely 
or too frequently, for an excess of copper would, of course, injure the 
ground permanently for any crop. 
