848 EXPEKIMET^T STATIO^f RECORD. [Vol.41 



injured as to have stopped growing. In some places beans adjoining the potato 

 lields had already been damaged. Within a week reports of injury to potatoes 

 by the leaf-hoppers had been received from practically all parts of the State 

 and later from other States, including Montana, North Dakota, South Dakota, 

 Minnesota, Michigan, and New York. 



" The first sign of trouble is usually a triangular brown ai-ea at the tip of 

 the leaf running back on the midrib. This is quickly followed by a progressive 

 burning of the margin, usually from the tip backwards but occasionally in more 

 or less triangular spots appearing along the margin, each one of these centered 

 in a lateral veinlet. These increase in area and the burnt margin increases 

 in width until nothing but a narrow strip along the midrib remains green, 

 and in serious cases this weakens and dies and the leaf shrivels up." 



Proof that the attack of the potato leaf-hopper {E. maU) is responsible 

 for producing hopperburn condition was obtained through cage experiments. 

 It was found that dahlias are attacked in the same way and with the same 

 effect produced on potatoes, its injury being quite serious in a number of locali- 

 ties. It has been found commonly on water sprouts and rapidly growing tips 

 of box elder trees, and has been known to attack fast-growing shoots of apple 

 stock in the nursery and rapid growing raspberry canes. This type of burning 

 is not produced by any other known leaf-hopper or other insect, and this leaf 

 hopper has not been found seriously injuring any plant in which the burning 

 does not occur. 



" To summarize the evidence then, it appears that leaf-hopper outbreaks 

 have been followed in every case by hopperburn epidemics; that these out- 

 breaks have occurred with little reference to temperature or moisture condi- 

 tions; that the distribution of burning in the field and upon vaieties has been 

 entirely with reference to time of planting and the flights of the leaf-hopper, 

 rather than to varieties or characteristic soil or moisture conditions ; that 

 no case of this type of burning has appeared in which the evidence of the leaf- 

 hopper work was not present, and no leaf-hopper attack has been known with- 

 out subsequent burning; that this insect produced this distinct and different 

 type of injury on other plants ; and finally, that in controlled experiments the 

 injury has been reduced or prevented at will." 



Studies indicate that most of the variation in susceptibility to attack by 

 different varieties of potatoes was due to difference in the time that these 

 plants developed sufficient foliage to furnish a place for egg deposition for the 

 spring brood of adults. Observations indicate that a single leaf-hopper may 

 seriously injure or even entirely destroy the margin of a leaf during its grow- 

 ing period. 



The author has studied the effect of the grape leaf-hopper on grapes and 

 woodbine, the rose leaf-hopper on roses and apple, and E. unicolor on apple 

 (which he points out should be known as the apple leaf-hopper), and finds 

 that these produce a similar injury, a characteristic white spotting which 

 appears more markedly on the upper surface of the leaf, although the punc- 

 tures are made from below. A comparison of box elder leaves attacked by 

 the grape leaf-hopper with those attacked by the potato leaf-hopper affords a 

 striking difference in the effect produced. It is thought possible that the dif- 

 ference in the method of feeding may account for the difference in effect, the 

 grape leaf-hopper and the apple leaf-hopper (E. unicolor) puncturing the mem- 

 branes of the leaf, while the potato leaf-hopper more commonly attacks the 

 veins. The author considers it more probable that the affection is due to 

 "some specific transmitted by the insect." The cage experiments showed that 

 where two or three were present on each leaf it took only a few days to de- 



