18 THE TOBACCO THRTPS. 



Nikoteen. — This is a preparation advertised as containing 40 per 

 cent of nicotine. It was applied in various strengths. Sprayed at 

 the rate of 1 part to 144 of water, 38 per cent of the thrips wer^ found 

 to be dead when the examination was made, twenty- four hours later. 

 No greater strengths were tried, as the cost of the insecticide would 

 not allow its use. 



Tobacco decoction. — This was made by boiling 1 pound of tobacco, 

 stems and leaves, in 1 gallon of water for a half hour. This strength 

 was very effective, practically all of the thrips that were fairly hit 

 by the spray being killed. Weaker strengths were less efficient. As 

 other forms of nicotine were found to be more effective in combination 

 with whale-oil soap, the latter was used with the decoction. When 

 so used, however, the mixture, owing apparently to some chemical 

 change which had taken place, burned the leaf. 



Whale-oil soap. — This was used in the proportion of 1 pound of 

 soap to gallons of water. When examined shortly after spraying 

 the thrips were seemingly as lively as ever. A strength of 1 pound 

 to 5 gallons killed about 50 per cent of the thrips, but seemed to 

 burn the leaf slightly. 



Glucose and )n olasses. — It was thought that possibly the thrips 

 might be caught or prevented from working on the leaf by means of 

 a sticky spray. A proportion of 1 quart of glucose to G quarts of 

 water was tried. While a few thrips were caught and killed by the 

 spray, others had escaped and were found, after the water had evapo- 

 ra'ted, walking about over the leaf without trouble. Molasses, also, 

 was tried, but found to be even less effective than the glucose. 



Dusting with lime or other powders seems to be of little value, as 

 the thrips are found making their way about through the dust with- 

 out trouble. Lime also has the disadvantage that it is not entirely 

 washed off by rains. 



Arsenicals were tried, but. as expected, seem to be of little value 

 when used for the thrips. 



Kerosene emulsion. — Since this is our strongest contact poison it 

 was thought from the first that if it could be used in sufficient strength 

 to kill the thrips without injury to the tobacco leaf, it would furnish 

 a satisfactory remedy. Experiments were made with the following 

 formula for the stock solution : 



Kerosene 2 gallons. 



Hard soap -h pound. 



Water 1 gallon. 



A strength of 1 part of stock solution to 10 parts of water proved 

 quite satisfactory in killing the thrips. This spray was found to 

 burn the leaves when used in the sun, but further experiments have 

 demonstrated that it can be used on a cloudy day or late in the evening 

 without danger of injury. 





