140 MASS. EXPERIMENT STATION BULLETIN 177. 



expected that the spraying operations of the average grower will result as 

 successfully as those reported here, where all possible care was taken to 

 thoroughly drench the plants. 



It should be kept in mind, however, that it is only necessary to reduce 

 the numbers of the plant lice 75 per cent, or more, when they can no 

 longer continue an aggressive attack that will result in serious injury, but 

 must take, figuratively speaking, a defensive position against their ene- 

 mies. The parasitic and predatory enemies of the plant lice are much 

 more resistant to contact sprays than the plant lice themselves, and in 

 no case with the insecticides used where the plants were not injured were 

 these beneficial insects destroyed, although they were present in numbers 

 when appUcation was made. The few plant lice which escape an eflacient 

 spray appUcation fall ready prey to these enemies. A report of the results 

 of these tests follows: — 



Material and Dilution. 



Plant Lice killed. 



Injury to Plants. 



"Black Leaf 40" (1-400) with soap, 



"Black Leaf 40" (1-800) with soap, 



"Black Leaf 40" (1-800) with Pyrox, i 



soap. 

 "Black Leaf 40" (1-1,000) with soap, 



"Black Leaf 40" (1-1,600) with soap, 



"Nico-Fume" liquid (1-750) with soa 



Fish-oil soap (1-5), 



Fish-oil soap (1-6), 



Fish-oil soap (1-8), 



Kerosene emulsion (1-9), 



Miscible or soluble oil (1-25), 



Miscible or soluble oil (1-40), 



Miscible or soluble oil (1-50), 



Miscible or soluble oil (1-64), 



Lime-sulfur, 34° Beaumd (1-22), 



Lime-sulfur, 34° Beaumfi (1-43), 



99-100 per cent., 



98-99 per cent., 



98 per cent., 



Not over 75 per cent., 



Ineffective, few killed, 



98 per cent., 



98-99 per cent., 



98 per cent.. 



Not over 50 per cent., 



90 per cent., 



Perfect kill, 



Perfect kill, 



98-99 per cent., 



98 per cent., 



Ineffective, not over 20 per cent., 



Ineffective, .... 



No injury. 



No injury. 



No injury. 



No injury. 



No injury. 



No injury. 



No injury ? 



No injury. 



No injury. 



No injury. 



Plants killed. 



Considerable injury. 



Some injury. 



Some injury. 



Some injury. 



No injury. 



Discussion of Results. 



1. "Black Leaf 40." — This material is perhaps the insecticide most 

 commonly used for the control of plant hce, but any of the other nicotine 

 preparations of a similar nature now on the market should give satisfac- 

 tory results. It is a concentrated solution of nicotine sulfate, containing 

 40 per cent, of nicotine by weight. It was tried with four dilutions — 

 1-400, 1-800, 1-1,000, and 1-1,600 — in each case, with the addition of 

 soap at the rate of 2 pounds to 50 gallons of the diluted "Black Leaf 40." 

 Both ordinary hard laundry soap and liquid soap were used with similar 



