36 MAINE AGRICULTUR-^I. EXPERIMENT STATION. 



circumstance which has led to the assiimptiori that the apple 

 alone was concerned in the life cycle of this pest, and the elm- 

 leaf curl which shelters the wolf in sheep's clothing has been 

 previously unsuspected of other danger than that which threat- 

 ened the elm itself, which except in the case of young trees is 

 not usually great. But the discovery of the annual migration of 

 a fresh infestation from the elm to the apple and the knowledge 

 that the elm generations are an essential portion of the life 

 cycle of the woolly aphid of the apple put a new significance 

 upon the economic status of the elm curl. 



There is probably no more interesting line of insect investiga- 

 tion than working out the full life cycle of the migratory 

 aphids and such projects find sufficient economic justification in 

 the fact that there are possibilities of control of certain species 

 of plant lice or aphids by such methods as rotation of crops 

 or the destruction of weeds which serve to maintain a species of 

 aphids dangerous to neighboring crops ; or the selection by the 

 landscape gardener of ornamental shrubs and trees which are 

 not susceptible to attacks of aphids common on native vegeta- 

 tion. In some cases circumventing the aphid by means of a 

 knowledge of its food habits and migrations would be simpler 

 and more effective than the direct methods of spraying which 

 need to be repeated each year of attack. 



Plant Pathoeogy. 



As was pointed out in the 191 1 report the department of plant 

 patholog}^ of this Station is equipped for making and does make 

 studies of diseases of the various economic plants of the State. 

 In the past, however, the work has been largely confined to the 

 diseases of the potato and the apple on account of the importance 

 of these crops and on account of the fact that, as a rule, suc- 

 cess or failure in potato and apple growing is to a great extent 

 dependent upon proper and efficent disease control. 



With regards efficiency in disease control, the commonest 

 methods of spraying potatoes illustrates a case in point. Spray- 

 ing potatoes for late blight is probably more widely practiced 

 and better done in Maine, as a rule, than in any otlier part of the 

 United States, but there is still much chance for improvement. 

 Much of the spraying is far from being efficient. Field studies 



