6 BULLETIN 866, U. S. DEPARTMENT OF AGRICULTURE. 



GENERAL CONSIDERATIONS. 



Butler (7) states that freshly prepared Pickering spray has a light- 

 blue color, which becomes deep blue on standing. He found a 

 neutral or acid Bordeaux, such as the Pickering sprays, to act more 

 quickly than ordinary Bordeaux, and reported that the Pickering 

 spray was less injurious to grapes than ordinary Bordeaux. He 

 states that the toxic value of the unit copper is the same in acid, 

 neutral, and alkaline Bordeaux, but is more available for immediate 

 action in the Pickering than in the ordinary Bordeaux sprays. 



According to Mc Alpine (15), who compared the results of Pickering 

 with those of standard Bordeaux sprays on apple trees, the two 

 varieties are equally effective in controlling black spot (Fusicladium 

 dendriticum). The limewater Bordeaux adhered just as well as the 

 standard Bordeaux, and had the additional advantages of being free 

 from gritty particles, of acting, at once on the spores of the fungus, 

 and of containing a much smaller percentage of bluestone. The 

 check trees gave 92.5 per cent of good fruit, indicating that the 

 black spot was not sufficiently severe to give definite results. 



F. de Castella (9) states that Pickering's claims concerning the 

 greater efficacy of the limewater sprays are not borne out in practice. 

 He reports that after extensive trial they have been found decid- 

 edly inferior to 2 per cent Bordeaux and that the use of Pickering 

 sprays can not be recommended. He considers the Woburn or 

 Pickering paste sold in England to be satisfactory but not superior 

 to Bordeaux. The greater solubility of the tetra-cupric sulphate 

 seems to be a defect rather than an advantage according to this 

 writer, for the reason that, while more active at first, it is removed by 

 heavy rains more readily than the ordinary Bordeaux deposit, thus 

 rendering the duration of the protection insufficient. No data are 

 given by this writer to substantiate his claims. 



PURPOSE OF PRESENT INVESTIGATION. 



If the results obtained by Pickering in the laboratory in England 

 hold true under field conditions in America, it is obvious that a great 

 saving in copper in this country may be effected. This investigation 

 was planned, therefore, for the purpose of outlining a practical 

 method of preparing a copper fungicide which would be more effective 

 per unit of copper than standard Bordeaux. The experiments were 

 conducted with the following primary objects in view: 



(1) To determine whether sprays made in accordance with the 

 various Pickering formulas (p. 3) were effective when applied under 

 American field conditions. 



(2) To ascertain how much copper in the form of the different 

 Pickering formulas is required per given quantity of spray to insure 

 effective control of fungous diseases. 



