12 DECIDUOUS FRUIT INSECTS AND INSECTICIDES. 



Mottier on August 3. At this date marry of the nymphs had devel- 

 oped to adults and these were very active. 



The blackleaf tobacco extract was used at a strength of 1 gallon 

 to 100 gallons of water and applied in the same manner as in the 

 previous experiments. Evidence of injury, namely, the yellowing 

 of the infested foliage, was already noticeable. Shortly after the 

 application was made, however, it was observed that the yellowing 

 and browning of the foliage ceased on the sprayed portion, whereas 

 on the untreated portion of the vineyard it increased, and by the end 

 of September the difference in color and vigor of the foliage on the 

 two blocks was very marked, although not so much so as in the 

 blocks that were sprayed about the middle of July before any of the 

 nymphs had attained full growth and developed wings. This indi- 

 cates that the best results can be obtained by treating the nymphs 

 before they commence to make too heavy a drain on the vines. An 

 additional reason why the earlier application of the tobacco extract 

 is desirable is that if it is applied earlier in the season, when the 

 nymphs are small, a weaker dilution may be used. There are thus 

 several advantages for the earlier application: First, the cost of the 

 material is reduced; second, the drain on the foliage wrought by 

 the large numbers of nymphs is checked ; and, third, the possibility of 

 tainting the berries of the fruit with the taste of tobacco— a condi- 

 tion that was slightly noticeable upon the fruit in the vineyard which 

 received the latest treatment of the season — is avoided. 



CONCLUSION. 



For several years past injury by the grape leaf hopper in the vine- 

 yards of the Lake Erie Valley has been confined to limited areas. 

 Its increase and dissemination during the season of 1910, however, 

 should be a warning to the vineyarclist to be prepared to combat it 

 during the coming season if the adults are at all numerous when the 

 vines " leaf out " in the spring. 



On account of the inability of the nymphs to escape from the under- 

 side of the grape leaves and because of the soft and unprotected con- 

 dition of their bodies the nymphal period is the most vulnerable stage 

 of the insect. Unfortunately this is the stage at which the insects 

 are the least conspicuous to the casual observer. For this reason in 

 vineyards where the adults are common in early spring an examina- 

 tion of the underside of the foliage should be made during the early 

 part of July. If the nymphs are at all numerous a single thorough 

 spray application of blackleaf tobacco extract applied to the under- 

 side of the leaves before wings are developed will reduce their num- 

 bers to such an extent that those remaining will neither seriously cur- 

 tail the growth of the vine nor impair the quality of the fruit. 



