6 
BULLETIN 19, U. S. DEPARTMENT OF AGRICULTURE. 
fruiting canes for bearing the next season's crop are selected. For 
the first season or two that a vigorous vineyard is infested, this stunted 
condition of the bearing canes is overlooked by all but the most 
observant vineyardists. With each additional season of heavy in- 
festation, however, it becomes increasingly difficult to secure well- 
placed, robust, bearing canes, and there is a corresponding decline 
in the quantity and quality of the crop until in some instances the 
Fig. 3. — Grape leaf shewing first evidence of whitened spots resulting from feeding of adult grape leaf- 
hoppers in early summer. ( Original. ) 
crop yield is so reduced that it pays little more than the season's 
cost of operating the vineyard. 
OCCURRENCE AND DESTRUCTIVE OUTBREAKS. 
In speaking of the occurrence of this insect Slingerland has said : 
''It has its periods of great destructiveness and comparative obscu- 
rity, or its 'ups and downs,' like most of our insects." It may exist on 
vines in limited numbers in some grape-producing section for several 
seasons without attracting much attention either in regard to its 
