196 INTERNATIONAL CONGRESS OP VITICULTURE 



these leaves have dropped from the vines. These insects become active with 

 the first warm days of spring and feed on a number of species of plants. The 

 most important are raspberry, blackberry, strawberry, burdock, catnip, Vir- 

 ginia creeper, currant and gooseberry but they have been found feeding on 

 the foliage of beech, sugar maple and various grasses when their preferred 

 food plants were missing. An interesting succession of plants used for food 

 in the spring has been noted. The leaf-hopper fed on burdock, grasses and 

 wild strawberry until the foliage of the raspberry and blackberry had ad- 

 vanced sufficiently for the young leaves to shelter the insects when they flew 

 to these latter plants, preferring the raspberry (both red and black). They 

 remained on this foliage for the space of nearly one month during which time 

 mating occurred. It may be of interest to mention that when these insects 

 are numerous they severely injure the leaves of cultivated raspberries dur- 

 ing May. By the latter part of this month the first grape leaves have grown 

 to a diameter of about two inches and the leaf-hoppers migrate to them. 

 Here they remain during June, lay their eggs and, later, die. The young 

 hatching from the eggs feed and develop on these leaves and remain on them 

 until they drop in the fall. Feeding during the warm days of autumn is 

 confined largely to the leaves of the strawberry and various grasses but they 

 feed on a number of other plants if these are present. 



Character and Extent of Injury. 



The grape leaf-hopper is a sucking insect and obtains its food by piercing 

 the tissues of the leaf and sucking the sap. The loss of sap would not inter- 

 fere with the economy of the vines but since a small area of the leaf dies 

 about each puncture, caused by the drying of the injured area, the presence 

 of many of these punctures interferes with the ability of the leaf to perform 

 its functions. An average sized leaf after being seriously infested until the 

 latter part of July was found to have about 20,000 such dead areas. Such 

 leaves have a yellow appearance, do not produce starch sufficient to meet the 

 needs of the vine and, as a consequence, infested vines do not develop the 

 required amount of wood, nor ripen the same, and the amount of fruit pro- 

 duced is, in time, considerably reduced. The decrease in amount of fruit is 

 greater the season following the infestation. By far the most serious injury 

 is caused by the failure of infested vines to properly mature their fruit. 

 Fruit from such vines is deficient in sugar and flavor and also contains more 

 acid than is found in well ripened grapes. Grapes from vineyards infested 

 with leaf-hoppers will not be used by the manufactures of the better grades 

 of grape juice nor are they suitable for use on the table or the making of 

 wines. They can be used to advantage, however, in the making of jellies 

 but as this industry is only in its infancy very few grapes are used for this 

 purpose. 



The actual loss to grape growers from this insect is difficult to esti- 

 mate. During years of ordinary infestation the damage caused in New 

 York state is not great; in fact in many regions it is not sufficient to war- 

 rant spraying to control the pest. It is during periods of abundance of 

 these insects that vineyards suffer and at such times the injury is sufficient 

 to cause loss. We estimate that this seldom exceeds $60.00 per acre for 

 two seasons, and that the injury in infested vineyards averages about $20.00 



