89 



TOTATO DISEASES AND THEIR TREATMENT. 



An article on Potato Scab, and remedies for it appeared in Bulletin 

 for June, 1900, (page 87). The following paragraphs deal with vari- 

 ous diseases affecting the potato ; they were written by Mr. B. T. Gal- 

 loway, Chief of the Division of Vegetable Physiology and Pathology 

 of the U. S. Department of Agriculture, as a Farmers' Bulletin" (No. 

 91). As attention is now being paid to the cultivation of potatoes 

 with a view to the export of " new potatoes" to England, it will be 

 advisable to note carefully any signs of disease and to apply the treat- 

 ment recommended at an early stage. 



Potato Leaf Blight, or Early Blight. 

 (Aiternaria solani (E. & M.) Sorauer.) 

 This disease is widespread and destructive. It is confined to the 

 leaves and green stems, and appears about the time the tubers begin 

 to form, but may be noticed earlier if the growth of the plants has 

 been checked in any way. The first indication of its presence is the 

 appearance on the leaves of grayish brown spots, which soon become 

 hard and brittle. The disease progresses rather slowly, the spots 

 gradually becoming larger, especially along the edges of the leaflets. 

 At the end of ten days to two weeks half of the leaf surface may be 

 brown withered, and brittle while the rest is of a yellowish green 

 colour. Three weeks or a month may elapse before all the leaves suc- 

 cumb. The stems in the meantime remain green, but they too finally 

 perish through lack of nourishment The tubers stop growing almost 

 as soon as the leaves are attacked, and as a result the crop is practi- 

 cally worthless. 



TREATMENT. 



Early blight may be held in check by the application of the fungi- 

 cide Bordeaux mixture. This is prepared and applied as follows : 

 Pour into a 50- gallon barrel 25 gallons of clean water ; then weigh 

 out 6 pounds of crushed bluestone, or copper sulphate, and after tying 

 it in a piece of coarse sacking suspend the package just beneath the 

 surface of the water by means of a string tied to a stick laid across the 

 top of the barrel. In another suitable vessel, such as a tub or half 

 barrel, slack 1 pounds of fresh lime. Slack the lime carefully by pour- 

 ing on small quantities of water at a time, the object being to obtain 

 as mooth, creamy liquid, free from grit. "When the lime is slacked, 

 add sufficient water to make 25 gallons. As soon as the bluestone is 

 dissolved, which will require an hour or more, pour the lime milk and 

 bluestone solutions together, using a separate ba r rel for the purpose 

 and stirring constantly to effect a thorough mixing. It sometimes 

 happens that sufficient lime is not add ; 1, and as a result the foliage 

 may be injured. To be certain that the mixture is safe, hold a steel 

 knife blade in it for two or three minutes and if the polished surface 

 of the blade shows a copper coloured tinge add more lime, but if it 

 stays bright the mixture is safe to use. Application of the mixture 

 should begin when the plants are 4 to 6 inches high, and should be 

 repeated at intervals of twelve to fourteen days until five or six treat- 

 ments have been made. By adding 8 ounces of Paris green to each 

 barrel of the Bordeaux mixture a combined fungicide and insecticide 

 is obtained, and this will prevent the attacks of the Colorado potato 



