Potato. 349 



under favorable circumstances over large portions of the foli- 

 age. There is also soon formed on the under side of the dis- 

 colored parts a frost-like coating, which is composed of the 

 summer spores and of the threads bearing them. Such a con- 

 dition is not present when the plants are attacked by the early 

 blight. The tubers of plants attacked by the phytophthora 

 almost invariably rot, and it is on this account that the losses 

 occasioned by the disease are often so great. It is supposed 

 that the tubers are infested by spores which fall to the ground 

 from the diseased leaves above, and not by the mycelium of the 

 fungus growing downward within the stem to the potatoes. 

 The spores are carried through the soil by descending water, 

 and upon reaching the potatoes they gain an entrance into the 

 tubers and cause the dry rot which is so destructive. It is pos- 

 sible, however, that the tubers may be reached by both methods. 



As its name implies, the late blight does not appear early in 

 the season. It rarely attacks plants before the middle of July, 

 and frequently not before the first of September. Consequently 

 there is abundant time for treating the vines, and the losses 

 from this disease need not be heavy. 



Treatment. The potato rot caused by this fungus can be 

 almost entirely prevented by the application of proper fungi- 

 cides. The work of Professor Jones of Vermont has clearly 

 shown that the disease can be controlled, and experiments made 

 in Europe have emphasized the same fact. Bordeaux mixture 

 is the best fungicide to use, as there is no danger of disfiguring 

 the crop, nor of injuring the foliage. It should be made at least 

 of "normal" strength, and when made according to the "stand- 

 ard " formula, it has been still more effective. But the latter 

 mixture is applied with considerable difficulty, so that thorough 

 applications of the former are to be advised. Treatments may 

 be begun any time during July, depending upon the time of 

 planting and the lateness of the variety. July 15th is generally 

 early enough for the first application in Xew York. It should 

 be followed by one or two others made at intervals of one to 

 three weeks, depending upon the weather. If the potato foliage 

 is thoroughly covered with the mixture, little trouble need be 

 anticipated from this disease. 



Bacterial Blight. Potatoes also appear to suffer from a bac- 

 terial disease which causes the death of the parts above ground 



