AMERICAN 
JOURNAL OF BOTANY 
Vol. X March, 1923 No. 3 
NOTE ON AN INDIRECT EFFECT OF SPRAYING POTATOES 
WITH BORDEAUX MIXTURE 
J. T. Rosa, Jr. 
(Received for publication January 16, 1922) 
Application of copper sprays to Irish potatoes has long been advocated 
for the control of the early and late blights, as well as for a supposed phys¬ 
iological effect of copper on the plants, whereby they are kept in a green, 
growing condition for a longer time than unsprayed plants. More recently 
attention has been called to the use of Bordeaux mixture for the control 
of tip-burn, by Erwin (3), and for the prevention of hopper-burn, by Dudley 
and Wilson (1). However, a spraying experiment on the horticultural 
grounds at Columbia, Missouri, conducted during the spring and summer 
of 1921, indicated that, under certain conditions, the application of Bor¬ 
deaux or other spray having similar physiological effects may produce 
indirect results which are undesirable. 
The variety used was Early Ohio, a good strain of which was obtained 
from northern Michigan and planted March 17, under uniform conditions. 
Four applications of 4-4-50 Bordeaux were made during May and June, 
both with and without arsenate of lead and nicotine sulphate. The sprayed 
plants remained green about three weeks longer (see fig. 1), and yielded an 
average of 34.2 percent more, than the checks, when dug August 28th. 
Since neither early nor late blight was present, but leafhoppers were nu¬ 
merous as usual after July 1, these results may be ascribed to tip-burn and 
hopper-burn control, and perhaps to other physiological effects. However, 
the tubers from the sprayed plots consisted to a large extent of knobby 
second growths, so that the actual quantity of marketable potatoes was 
really much less than from the check plots, the tubers of which showed 
second growth only to a moderate extent (see fig. 2). 
The Early Ohio, which is the leading variety at present in the lower 
Corn Belt, seems much more subject to second growths of the tubers than 
other varieties grown at Columbia the past four years. Perhaps such 
varieties as the Irish Cobbler, which has little tendency to second growth, 
would react quite differently if subjected to spraying treatment under the 
same conditions as those mentioned in the test with the Early Ohio variety. 
If the increase in yield can be secured, without distortion of the tubers, 
[The Journal for February (10 : 57-112) was issued March 2, 1923.] 
113 
