﻿38 BULLETIN 19, U. S. DEPARTMENT OF AGRICULTURE. 



tion on the purple surface of the ripened grapes, rendering them 

 unattractive for table use. 



During the last few years commercial brands of tobacco extracts 

 have come much into use as liquid spray substances for the control 

 of soft-bodied sucking insects. Hence once more, after a period of 

 over 80 years since it was first recommended, tobacco appears to be 

 the most promising insecticide for the control of this pest. 



During the seasons of 1910 and 1911 the grape leafhopper was 

 present in very injurious numbers in many vineyards in the Lake 

 Erie Valley. Vineyard experiments were undertaken by the Bureau 

 of Entomology in the vicinity of North East, Pa., using the tobacco 

 extracts as liquid sprays against the nymphs. The results of these 

 experiments were very gratifying, since with one thorough applica- 

 tion of the tobacco extract the numbers of these insects in the treated 

 vineyards were so greatly reduced and the injury was so slight that 

 the foliage retained its dark green color throughout the season, the 

 cane growth was strong and well matured, the berries were large, the 

 fruit sweet, and the size of the crop considerably increased ; whereas, 

 on the untreated portion of the vineyards the foliage turned brown 

 and dropped prematurely, the cane growth was stunted, the berries 

 were undersized and lacking in sugar content, and the tonnage per 

 acre was much less than on the sprayed portions of the vineyards. 



Detailed reports of these vineyard experiments against this pest 

 are given in Part I of Bulletin No. 97 and Part I of Bulletin No. 116 

 of this bureau. 



SPRAY MATERIAL. 



The forms of tobacco extract used in these experiments in 1910 

 and 1911 were the blackleaf tobacco extract containing 2.70 per cent 

 nicotine sulphate and the blackleaf tobacco extract containing 40 

 per cent of nicotine sulphate. The blackleaf tobacco extract con- 

 taining 2.70 per cent of nicotine was effective in killing all of the 

 nymphs which were thoroughly wetted by the spray, when applied 

 at a dilution of 1 part of tobacco extract to 150 parts of water or 

 Bordeaux mixture. The blackleaf tobacco extract containing 40 

 per cent nicotine sulphate was found to be effective at a dilution 

 of 1 part of tobacco extract to 1,500 parts of water or Bordeaux 

 mixture. Both of these forms of tobacco extract appear to be 

 equally effective in destroying the nymphs at the dilutions men- 

 tioned. The one containing the smaller percentage of nicotine 

 (2.70 per cent), however, necessarily contains more sticky inert mat- 

 ter. When this is applied as a spray to the vines late in the season, 

 i. e., toward the middle of August, and when little rainfall occurs 

 before the harvesting season, some of this sticky substance may ad- 

 here to the ripe grapes, giving the skins a slight flavor of tobacco. 



