14 Circular 107 



under-sides of the foliage in different parts of the field. In this way 

 the writer believes the infestation will be discovered before the plants 

 assume a recumbent habit and therefore while effective spraying of 

 them is still practicable. Colonization of the plants will be indicated 

 not by the presence of an occasional winged plant louse on the 

 foliage (they may be merely passing migrants of a species never us- 

 ing the plants of the nightshade family for food), but by the finding 

 of winged lice each with a few tiny greenish-white young about her. 



When the presence of lice indicates that spraying is necessary, 

 (1) kerosene emulsion, (2) whale-oil soap, or (3) 40 per cent, nico- 

 tine, soap and water, may be employed. The first is cheap but diffi- 

 cult to make, and the margin between the strengths to kill the lice and 

 to damage the plants is relatively narrow. The second is easy to 

 prepare but the probable margin of safety is small. The third is 

 more expensive but is easy to prepare, and the margin of safety be- 

 tween amount necessary to kill the louse and that dangerous to the 

 plant is wide. 



The writer for the present feels justified in recommending nico- 

 tine, soap and water as the best combination for this work. He rec- 

 ommends one part of 40 per cent nicotine to 500 parts of water to 

 which soap is added at the rate of from 2 to 4 or 5 pounds to 50 gal- 

 lons. The greater strength of soap is recommended when the water 

 is not soft. Whale-oil soap is perhaps preferable to that used for 

 laundry purposes, although any brand of the latter free from resin- 

 ous matter will be found pretty satisfactory. 



Having secured the material the means of applying is the next 

 problem. When the crops are field-grown on a large scale, a power 

 sprayer is a necessity. In small garden plots a knapsack sprayer or 

 even a compressed air cylinder may be used with satisfactory results 

 because the lack of pressure can be made up for by the care with 

 which the infested plants are covered. In field spraying the most 

 practicable machine the writer has seen is a regular potato spraying 

 machine furnished with an engine-driven pump, which maintains 

 constantly while at work a pressure of approximately 250 pounds to 

 the square inch, and three properly set nozzles to each row. The 

 side nozzles must be so set that one side of the entire plant from top 

 to soil is covered by the cone made of discharging spraymaterial from 

 one nozzle and the other side similarly covered by the cone from the 

 other nozzle, and the top is completely within the cone of spray ma- 

 terial from the nozzle located above the row. In dealing with pota- 

 toes and tomatoes 100 gallons or more to the acre will probably be 

 necessary. Saving spraying material by reducing the application is 

 bad practice, for the chances of killing a sufficient percentage of the 

 lice are none too good even when the most careful work is done. 



