EFFECT OF GERMICIDES ON PLANTS. 201 
the varieties used. He recommends for practical purposes a solution of 1 ounce to 1 
gallon for 2 hours, followed by 1o hours treatment with lime. 
GERMICIDAL TREATMENT OF DORMANT PLANTS. 
Plants in the resting condition, especially roots and shoots protected by cork, will bear 
relatively strong doses of germicides. Bordeaux mixture (6:4:50), copper sulphate solution 
(3:50), mercuric chloride water (1:1000), soap and lye solutions, lime washes, cold boiled 
or hot boiled lime sulphur solution, lime-salt-sulphur wash may be applied rather freely. 
A few formule are given at the end. 
A more difficult and important problem concerns the use of germicides and insecticides 
on growing plants. 
GERMICIDAL TREATMENT OF GROWING PLANTS. 
In the treatment of growing plants two things must be kept in mind constantly: 
(1) The foliage must not be injured; (2) the applications must be effective. A third 
very desirable quality in a germicide is adhesiveness, since if the substance is washed off 
by every rain the necessary reapplications will be expensive. 
Bordeaux mixture containing an excess of lime, e.g., formula 4:6:50, or 4:4:50 is borne 
very well by some plants. The foliage of others is liable to be burned, especially if the spray- 
ing is not repeated frequently either with Bordeaux or with milk of lime so as to keep an 
excess of lime present on the leaves. This mixture is an effective fungicide and also has 
some value as a germicide. Pierce used it on walnut blight in California with partial success. 
It might perhaps be used to protect from some of the leaf spots. Always, however, it is 
advisable to try the experiment on a small scale first, until the general effect of the copper 
on the foliage has been determined. The writer has seen a whole peach orchard defoliated 
in midsummer by the improper use of Bordeaux mixture. 
Copper absorbed in minute quantites, has a stimulating effect on growth. Chester 
observed this in 1890 while testing the effect of copper salts on Vitis. He says that Bordeaux 
mixture seems to stimulate the growth of the vines. 
, In 1894, Frank & Kriiger stated that the assimilation of potato leaves is increased, the 
transpiration becomes greater, the leaves live longer, the harvest is increased, and the tubers 
contain more starch when the plant has been treated with copper salts, especially “the 
ordinary 2 per cent copper vitriol-lime mixture.”’ 
In 1895 Galloway and Woods showed that Bordeaux mixture could be used with safety 
on growing grape-vines and potatoes, and observed that copper salts stimulated the growth 
of these plants. 
In 1898, Harrison stated that Bordeaux mixture has an invigorating effect on the foliage 
of plum, pear, peach, and quince. 
In 1898, Starnes in Georgia reported injury to peach foliage from copper salts sprayed 
thereon. 
In 1899, Duggar obtained shot-hole effects on peach foliage as the result of the use of 
copper fungicides. 
In 1900, Pierce published his observationson the physiological stimulation of Bordeaux 
mixture on peach leaves. 
As a result of his researches, published in 1902, Bain concludes that peach leaves are 
especially sensitive to poisons in general and to copper in particular. 
The self-boiled lime-sulphur mixture is less injurious to the leaves of peach and plum 
trees than Bordeaux mixture, and appears to be an equally good germicide. Scott has used 
it on peaches for the prevention of the leaf-spot due to Bact. prunt, and with brilliant suc- 
cess in the summers of 1909 and 1910 for prevention of the brown rot due to Monilia. It 
should be tried also for the prevention of the walnut blight due to Bact. juglandis. 
