THE EUROPEAN CORN BORER AND ITS CONTROL. 63 



of these ears were only damaged to a slight degree, however, and in general' 

 were in a much better condition than those in the check rows. 



About 52 per cent of the tassels were broken over in the sprayed plot 

 while 61 per cent were broken over in the check rows. 



The stalks of the sprayed plants were all infested by the pest, but 

 surface feeding had been entirely prevented. The sprayed plants had 

 a much better (greener) color than the plants in the check rows. Late 

 in October most of the plants in the check rows had fallen over as a result 

 of P. nuhilalis attack, but only about 10 per cent of the sprayed plants 

 had done this. 



The results of this experiment indicate that many of the European 

 corn borer larvae can be killed by the application of arsenicals at the right 

 time, but that the damage to the plants by the insect cannot be prevented 

 to a paying degree. 



Corn grows very rapidly throughout the period when spraying is neces- 

 sary, and the newly developed portions of the plant are the favorite 

 points of attack, viz., bases of the leaf sheath, surface of the leaf blade, 

 and the tassel. Tliis necessitates frequent sprayings in order to combat 

 the larvae of the pest, which hatch over quite an extended period of time. 

 The cost of sprajdng large areas would, therefore, be probably prohibitive. 



Spraying with Calcium Arsenate. 

 Three applications of calcium arsenate, at the rate of one-haK ounce of 

 the powder to 2 gallons of water, were made on the same date and in the 

 same manner as have been detailed for lead arsenate. The results were 

 practically the same, although calcium arsenate appeared to be more 

 satisfactory in its prevention of injury than did lead arsenate. 



Cultural Practices to avoid Damage. 



Several observations made during the summer of 1918 seemed to 

 suggest the possibihty that damage by the borer could be avoided by 

 regulating the time of planting corn so that the plants would not be at a 

 stage to attract the female moths of the insect during their time of activity. 

 The female moths prefer to deposit their eggs upon some plant bearing a 

 soft, green seed head. If corn plants bearing a tassel are not available 

 the females habitually deposit their eggs upon some other species of host 

 plant that bears a seed head in the desired stage of development. 



It was observed that adjoining corn fields, in different stages of develop- 

 ment, were often infested in varying degrees by the insect. In one 

 market garden at West Medford, Mass., a field of sweet corn, planted on 

 April 1, 1918, was very severely infested by the borer. An adjoining 

 field of sweet corn, planted about April 10, 1918, was only infested to a 

 moderate degree. A third field of sweet corn, planted about April 30, 

 1918, was practically free from the pest, and an examination of the ears 

 when harvested showed only a very small per cent of injury. 



