1920] DISEASES OF PLANTS. 843 



water with which the mixture was made had little influence on the adhesive 

 quality. Deteriorated Bordeaux mixture 1 : 1 was said to be more adhesive 

 than deteriorated Bursiindy mixture. The copper acetate solutions were more 

 adhesive than Bordeaux mixture, and the addition of ferrous sulphate to Bor- 

 deaux mixture was fouud to decrease the adhesiveness in a very marked degree. 

 The addition of Paris green or arsenite of soda did not change the adhesive 

 property, but lead arsenate increased it slightly. The addition of casein to 

 Bordeaux mixture 1 : 1 did not affect the adhesiveness, while the addition of 

 gelatin to normal and basic acetate of copper increased the adhesiveness of both 

 salts. Cuprammonium sulphate was found more adhesive than Johnson's mix- 

 ture. The proprietary copper fungicide and arsenical insecticide, Pyrox, pos- 

 sessed a fair degree of adhesiveness, but were noticeably inferior to 1 per cent 

 Bordeaux mixture plus 0.5 per cent arsenate of lead. 



Pickering sprays, F. C. Cook (U. S. Dept. Apr. Bui. 866 {1920), pp. 1ft, pis. 

 2, fig. 1). — Results are given of an investigation carried on by the Bureau of 

 Chemistry in cooperation with the Bureau of Plant Industry and the Maine 

 Experiment Station to determine the efficacy of the so-called Pickering sprays, 

 which are prepared by mixing saturated limewater with dilute solutions of 

 copper sulphate and contain their copper in the form of basic copper sul- 

 phates. 



Two formulas of Pickering sprays were used, one composed of 1 oz. of copper 

 sulphate to 134 oz. of limewater ; the other, 1 oz. of copper sulphate to 161 oz. 

 of limewater, these fungicides being compared with ordinary Bordeaux mix- 

 ture composed of equal parts of copper sulphate and lime. Experiments 

 were conducted to determine whether sprays made in accordance with the 

 various Pickering formulas were effective when applied under American field 

 conditions, and to ascertain how much copper in the different Pickering formu- 

 las is required per given quantity of spray to insure effective control of fungus 

 diseases; also, to compare the fungicidal values of the sprays with standard 

 Bordeaux mixture, and to determine the injurious action of the Pickering sprays 

 on various kinds of vegetation. 



The strongest Pickering sprays, those containing from 0.6 to 0.7 per cent of 

 copper sulphate, were found to control fungus diseases on potatoes and cran- 

 berries very effectively. Their control on grapes and apples was not definitely 

 determined, as the results were complicated by burning or other injury to the 

 foliage and fruit. Pickering sprays containing less than 0.6 per cent of copper 

 sulpliate were not so effective for potatoes and probably not for cranberries. 

 No difference between the efficacy of sprays made by the two formulas was ob- 

 served. 



The results of the tests made on potatoes indicated that per unit of copper 

 present the sprays were twice as effective as Bordeaux mixture. Increased 

 yields of tubers were obtained on plats of potatoes treated with Bordeaux 

 mixture and with the stronger Pickering sprays, indicating that both fungicides 

 exerted a protective action on the potato plants. 



The adhesive properties of Pickering sprays were found to vary with the 

 foliage to which they were applied. They adhered to potato and cranberry 

 leaves in practically the same degree as Bordeaux mixture, to apple leaves In 

 a somewhat higher proportion, and to grape leaves in a lower proportion. No 

 .injurious effects followed the application of Pickering sprays to potatoes in 

 aine or to cranberries in New Jersey. The sprays, however, proved too caustic 

 for use on the apple in Virginia and grapes in New Jersey and Virginia. On 

 this account Pickering sprays are not recommended for use on tender foliage. 



I Barium water sprays, made with barium hydrate and containing 0.7 per cent 

 copper sulphate, proved very successful as a fungicide for potatoes, and such 



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