EFFECT OF GERMICIDES ON PLANTS. 201 



the varieties used. He recommends for practical purposes a solution of i ounce to i 

 gallon for 2 hours, followed by 10 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 formulae 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 observations on 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 Bad. pruni, and with brilliant suc- 

 cess in the summers of 1909 and 19 10 for prevention of the brown rot due to Monilia. It 

 should be tried also for the prevention of the walnut blight due to Bad. juglandis. 



