K^EW YoKK Agkicultukal Experiment Station. 377 



cation the younger nymphs were killed with somewhat weaker 

 solutions but that the older nymphs would escape unless the work 

 was carefuly done. On the basis of the nicotine content, the proper 

 dilutions for mixtures to control the grape leaf -hopper are " Black 

 Leaf Tobacco Extract " one part to 150 parts water, and " Black 

 Leaf 40 " one part to 1600 parts water. 



In the tests it was very apparent that the older the nymph the 

 greater its power of resistance to the mixtures. It required less 

 material to kill the younger nymphs. Even a fine-mist spray 

 will suffice for the very immature insects, but it will not prove 

 effective against the larger nymphs. The adult insects are fre- 

 quently hit while on the wing, but as a rule they are affected in 

 too small numbers to be considered in the spraying operations. 



The experiments also proved that the most .satisfactory results 

 can only be attained when the material is applied with a pressure 

 of about 125 lbs. and nozzles are used that throw a coarse spray 

 against the under sides of the leaves. !N^ozzles throwing a mist 

 spray, even if a high pressure is maintained, will not cover the 

 insects sufficiently to kill them ; and nozzles throwing a coarse 

 spray are ineffective with low pressures. This is especially true 

 when using an automatic leaf-hopper sprayer (described below) 

 or when the trailing-hose outfit, operated by hand, is employed. 

 Even with hand-,spraying, the men operating the nozzles must be 

 very careful to do thorough work or failure will result. Efficient 

 results were always obtained when the vines were thoroughly 

 sprayed. 



One objection to the use of nicotine sprays when applied by 

 means of " trailers " is the saturation of the clothes of the men 

 handling the nozzles. This has caused nausea in several in- 

 stances and led to attempts by various growers to arrange fixed 

 nozzles to throw the spray on the under sides of the leaves. These 

 devices were failures as they did not do thorough work on vines 

 with heavy foliage. Among the various contrivances that Avere 

 devised was one made by llr. E. A. Iforehouse which had some 

 good points but, however, several serious faults. In order to 



