136 BOARD OF AGRICULTURE. [J^H , 



some obscure wilt troubles in our potato fields, though as yet 

 the writer has not recognized this as the cause. In the tubers, 

 however, it has been found as a very common agent of decay, 

 with the bacterial rot being largely responsible for the trouble 

 a year ago. The disease usually begins at the stem end, form- 

 ing a slow dry rot. Not unfrequently bacteria occur with it 

 and help the rot along. When the infected tubers are placed 

 in a moist atmosphere the fungus breaks out on the surface in 

 small white fruiting tufts. The decay continues in the cellar, 

 though probably not so vigorously as in the fields, especially 

 after the tubers become dried out. Often tubers show the pres- 

 ence of the fungus only in cross section by a slight discolora- 

 tion of the bundles. These tubers, when planted, no doubt 

 help to perpetuate the disease. 



Because the fungus develops inside the tissues of the tuber, 

 seed treatment is of little value against this trouble. Our pre- 

 ventive measures so far are limited chiefly to the selection of 

 seed tubers free from the fungus. 



6. True Blight or Downy Mildew is the last and most 

 important of these parasites of the potato. It is an old trouble, 

 has proved very injurious in Europe and here in years past, 

 and has been much studied both to gain facts in its life history 

 and to prevent its ravages. Blight first appears on the potato 

 leaves in this State anywhere from the first of July to the latter 

 part of August. Its time of appearance and the severity of 

 attack depend on weather conditions. If after its appearance 

 there occurs a moist or muggy period of several days' duration, 

 it develops with surprising swiftness and carries off the vines 

 in a short time. The fungus produces blackish areas, usually 

 beginning at the tip or margin of the leaves, and these increase 

 more or less rapidly according to the weather. Examining 

 the underside of an infected leaf the fruiting stage is seen as a 

 faint whitish growth at the juncture of the diseased and 

 healthy tissues. In dry weather these moist blackened tissues 

 dry up. Under favorable conditions the disease progresses 

 so rapidly that there soon remain only the green stems and 

 these then die as a result of the death of the leaves. In a week 

 the blackened dead stems will wither up. Inconspicuous leaves 

 may take the place of the former luxuriant green field. 



Occasionally one sees diseased spots on the stems, but so 

 far as I have been able to observe we have no reason to believe. 



