750 ANNUAL REPORT OF THE Off. Doc. 



the less is the auiouut of moisture preseut; the contrai-j is also true. 

 The decay does uot take place in a uuiform mauner, but its progress 

 varies in diflereut tubers. lu some it is mostly the parts near the 

 surface that are affected, while in others the disease may advance 

 rapidly towards the center of the tuber, causing the exterior to show 

 a much smaller amount of disease than is actually present. The 

 discoloration, however, generally presents a uniform appearance. 

 Although it is by no means impossible for the mycelium to reach the 

 tubers from the leaves by means of the stems, still it is the generally 

 accepted opinion that infection does not take place in this manner. 

 This belief was held many years ago, for in some of the earlier writ- 

 ings, recouimendatiot»s mny be found in which very high hilling is ad- 

 vocated so that the spores may be washed past the tubers and away 

 from them, and not through the soil directly to them. 



"There is still another feature of the late blight which it is well 

 to bear in mind. The disease generally appears during August and 

 vSeptember, although earlier and later attacks are not very rare. 

 Coming so late in the season, all the earlier varieties are compara 

 lively free from attack, but the latter ones are especially subject to 

 the disease. This, however, is not necessarily due to the foliage of 

 such varieties l)eing more susceptible, but rather to the habits of the 

 fungus. 1 have not observed that the age of the potato plants has a 

 marked influence upon the spread of the disease; nor that the young 

 foliage of the plants is less subject to the disease. It appears as if 

 the parasite is able to thrive upon all potato foliage which is in a 

 healthy condition at the time of the germination of the spores, and 

 that old and) young foliage or plants suffer practically to an equal 

 extent. 'Acceptable evidence of a resting stage, or oosporic form of 

 this fungus is lacking, and many believe that the fungus threads sur- 

 vive the winter in the partially diseased tubers.' 



"The important question and the question which concerns every 

 potato raiser is, '1& there any practical remedy or preventive for the 

 potato blight?' Fortunately there is, and there is no more reason 

 now for a farmer to permit his potatoes to be destroyed by the 

 blight than to permit them to be destroyed by the potato-beetle. The 

 standard preventive is the Bordeaux mixture. This, if properly 

 made and properly applied, will protect potatoes from the late blight 

 and the consequent potato rot. 



"Making the Bordeaux Mixture. — No doubt failure to secure satis- 

 factory results from the use of Bordeaux mixture is often due to the 

 fact that the mixture is not properly prepared. AN'hile its prepara- 

 tion is very simple it is possible the very simplicity has caused some 

 to think no great care need be exercised in its preparation. This is 

 a mistake, for the success of the application depends upon its being 

 made properly. 



