242 INSECTICIDES, FUNGICIDES, AND WEED KILLERS. 



and Kruger are of a contrary opinion. They have shown that sound 

 potatoes sprayed several times in the year, have a more vigorous 

 growth and a greater vitality than untreated plants. The copper 

 treatment increases the crop of tubers (Gutzeit), even in dry seasons, 

 when the disease is not to be feared, in the ratio of 100 to 163, and 

 according to Leydhecken by 2 per cent. These observers reckon that 

 the bouillie bordelaise treatment is imperative in all cases, because 

 it is ahvays followed by an increased crop, whether the copper acts 

 as a stimulant of the plant or whether it prevents the invasion of 

 parasites, so numerous as to lower the assimilative capacity of the 

 leaves by the greater or less damage which they produce in them. 

 The disinfection of seed potatoes, and the treatment of the stems 

 with bouillie bordelaise, always protect the cultivator from those 

 sudden outbursts of potato disease, and enables him to produce uni- 

 formly good crops. The phytophthora does not attack potatoes alone, 

 but other plants of the SolanecB family, such as the tomato 

 {LicojJersicum). What has been said as regards the potato applies 

 to this plant. Pellegrini successfully treated this disease with a 

 bouillie of 3 per cent blue vitriol and 1 per cent of lime. By three 

 sprayings on tomatoes already attacked, the first on 15 June, the 

 second on 2 July, and the third on 15 July, Howell succeeded in 

 getting 4 per cent ol diseased fruit on the treated plot, against 60 per 

 cent on the untreated plot. 



PhytopJitkora Fhaseoli, Thaxter (Lima bean mildew). — This phyto- 

 phthora devastates the haricot {Phaseolus lunatus) fields of America. 

 Bturgis treated this fungi successfully with bouillie bordelaise. 



Peronospora viticola, De By. (mildew of the vine). — If the water 

 favourable to the development of the spore contains the most minimum 

 amount of copper the conidia does not hatch, or if it hatches, the 

 germination tube cannot penetrate into the leaf. The object of the 

 bouillie bordelaise treatment is thus to prevent the conidia from forming 

 new hotbeds of infection by stopping its evolution. It wall be seen that 

 the amount of copper to be deposited on the leaves need not be great 

 to produce this effect, and that a weak bouillie bordelaise may have 

 the same action as the concentrated bouillie formerly used. But it is 

 not possible to go below certain limits. Trials made with 0-5 per cent, 

 and even 0-1 per cent, have shown that, if the action of the copper is 

 still perceptible, with 0*1 of blue vitriol in the bouillie bordelaise, that 

 strength can no longer entirely prevent the hatching of the disease. 

 After the use of a 0'5 per cent bouillie there may still remain some 

 rare leaves attacked by mildew. The 1 per cent bouillies, on the 

 ^contrary, are always sufficient, and absolutely as efficient as the 

 classical 2 per cent bouillie. In most cases this 1 per cent bouillie is 

 used. The 0-5 per cent bouillie is used when the treatments exceed 

 five in a year. By seven treatments with a 0-5 per cent bouillie, 

 Galloway got 99 per cent of sound grapes. It is, in fact, better to 

 renew a thin copper deposit on the leaves and grapes often than to 

 spread a thick layer two or three times a year ; the organs are con- 

 tinually growing, and washed by the rains. The great point is to 

 eovev all the surface of the vine uniformly with bouillie bordelaise by 



