O MAINE AGRICULTURAL EXPERIMENT STATION. 



which so far have been found to be non-parasitic, appear to be 

 carried with the tubers, and tubers from diseased hills usually 

 produce more seriously affected plants than those from which 

 they came, a wise Maine grower will not temporize with them. 

 He will eliminate the diseased plants as soon as they appear 

 in his fields and before they begin to set tubers. If the disease 

 occurs in his fields to such an extent that this practice is im- 

 possible, he will dispose of the entire crop and endeavor to 

 secure seed for his .next year's planting from fields which 

 showed none of these troubles. 



These leaf and stem troubles are known variously as wilt, 

 leaf-roll, curly dwarf, rosette, mosaic, etc. Mosaic is the only 

 one which occurs to any extent in Maine. Of the two leading 

 varieties grown it is almost entirely confined to the Green 

 Mountain, practically none being seen on the Irish Cobbler. 



Mosaic is characterized by more or less wrinkled, irregular, 

 distorted foliage of a variegated color. The leaves are vari- 

 ously spotted and mottled with a lighter green, giving a calico 

 effect. No definite parasite has been found associated with it. 

 It certainly indicates a weakness of the seed, and should be 

 eliminated wherever it occurs. 



Potato wilt, wherever found, is undoubtedly of a parasitic 

 nature. Apparently a similar type of disease may be caused by 

 two different types of fungi. This is not particularly important 

 to us, but it is important from the standpoint of the practical 

 grower to know that potato wilt is carried by the seed tubers 

 and that once in the soil the fungus which causes the disease 

 may persist there for an undetermined time. So far we have 

 seen very little of it in Maine and it is much less prevalent 

 here than in any other of the leading potato growing states 

 visited. 



While wilt may appear earlier it does not usually show up 

 in a striking manner till about blossoming time or later. In 

 the earlier stages the affected plants may be lighter green, and 

 later even take on a yellowish appearance. The lower leaves 

 begin to die first, and thus it is often overlooked by the aver- 

 age observer. His attention is usually attracted by the pre- 

 mature death of the plants, following a wilting or withering 

 of the upper leaves. 



