\... -J.] MODERN POTATO CULTURE. 



of attack by this blight. The Bordeaux mixture tonus a 

 coating of copper which prevents the entrance of the blight 

 into the tissue of the leaf. 



Potato Blight, Late Blight or Hot. 



This disease attacks the leaves, stems and tubers. Gen- 

 erally the first noticeable effect upon the leaves is the sudden 

 appearance of brownish or blackish areas, which soon be- 

 come soft and foul smelling. So sudden is the appearance 

 of the disease in some cases that fields which one day look 

 green and healthy may within the next day or two become 

 blackened as though swept by fire. The rapid spread of the 

 disease, which is caused by a parasitic fungus, is dependent in 

 large measure upon certain conditions of moisture and heat. 

 A daily mean temperature of from 72° to 74° F. for any 

 considerable time, accompanied by moist weather, furnishes 

 the best conditions for the spread of the parasite. On the 

 other hand, if the daily temperature exceeds 77° for a few 

 days, the development of the disease is checked. This fact 

 explains why the fungus seldom occurs to any serious extent 

 in sections where the mean daily temperature exceeds 77° 

 for any length of time, and probably why it appears later 

 than the so-called early blight. 



This fungous disease is an old offender, and until quite 

 recently has been regarded as the most serious enemy the 

 potato grower has to deal with. Because of the difficulty, 

 in mild cases, of distinguishing between this and the early 

 blight, much of the damage of the latter has in the past been 

 overlooked or attributed to the late blight. In all severe 

 cases it is accompanied by a strong, disagreeable odor, which 

 is easily recognized after it has once been experienced. 



Unlike the early blight it attacks strong, healthy plants as 

 freely and readily as those that have been partially eaten by 

 the flea beetle or Colorado potato bug. The age of the po- 

 tato plant has little influence upon the spread of the disease. 

 Apparently the fungus is able to thrive upon all potato foli- 

 age, and old and young foliage and plants suffer equally 

 from its attacks. The late blight not only stops the growth 

 of the tubers but causes them to rot. 



