Plant-Diseases and Insects. 



123 



for early and late varieties, but it is sometimes necessary to 

 make one to two more. Probably the best time to make the ap- 

 plications is on a still, sunny day. The liquid can be more uni- 

 formly distributed when no wind is blowing, and if it dries 

 soon after being applied, the lime and copper adhere very 

 firmly to the leaves. 



" The , quantity of the Bordeaux mixture to apply to a 

 hectare cannot be definitely stated, for it varies with the va- 

 riety of potato grown, with the amount of leaf-surface, 

 the method of cultivation, etc. Counting 55,000 plants 

 to a hectare, from six to eight hectolitres* are neces- 

 sary for the first application, and from ten to twelve for the 

 later ones. 



"Most of the substances which are used against fungi are 

 also recommended, but those containing copper are probably 

 the best. The value of powders is doubtful, for they are 

 harder to apply and their action is not so certain. 



"Conclusions. — 1. The Bordeaux mixture which contains 

 3.3 pounds of copper sulphate and 1.1 pounds of lime, is as Treatmen , 

 efficient as that containing 4.4 or 6.6 pounds. It is even of potato- 

 probable that 2.2 pounds of the sulphate is sufficient. rot - 



"2. The treatment, so far as possible, should be preventive. 



" 3. The probabilities that a curative treatment will be suc- 

 cessful are only slight, unless the disease is also checked by 

 some natural causes, such as a north wind, prolonged draught, 

 or the absence of dew. 



"4. The first application should be made 8 to 10 weeks after 

 planting, and the following ones at intervals of 18 to 20 days. 

 But during a rainy season the applications should be repeated 

 about every two weeks, and for late varieties, at least three 

 should be made to save any considerable portion of the crop. 



"5. From 6 to 8 hectolitres per hectare are required for the 

 first application ; the later ones require from 10 to 12. 



" 6. The yield of tubers from varieties which are said to be 

 free from attack is markedly increased by applications of 

 the Bordeaux mixture. 



" 7. Most fungicides are effective in the treatment of the po- 

 tato crop, and the copper compounds are particularly valua- 

 ble in this respect." 



*A hectolitre is 26.41 gallons. 



