POTATO PLANT LICE AND THEIR CONTROL. 143 



the kerosene emulsion per gallon of the diluted spray is something over 1 

 cent, or approximately the same as for the "Black Leaf 40" and the fish- 

 oil soap solutions. 



6. Miscible or Soluble Oils. — One of the standard commercial brands of 

 miscible oils was used in these tests, this being tried with four dilutions, — 

 1-25, 1-40, 1-50 and 1-64. This material in all four dilutions showed a 

 very high killing efficiency, but even at the greatest dilution, 1-64, showed 

 distinct oil injury to the potato foliage. In justice to this material, how- 

 ever, it must be said that the sample experimented with was not perfect, 

 as there was some free oil evident, an ever-present danger, nevertheless, 

 with this material. Time did not permit obtaining a fresh sample of mis- 

 cible oil, so that this material must be placed in the questionably danger- 

 ous class until further experiments prove to the contrary. The cost of 

 this material is less than that of any of the other insecticides referred to, 

 and obtained in any quantity would amount to less than 1 cent per gallon 

 of diluted spray material, 



7. Lime-sulfur. — A standard commercial brand of this material, hav- 

 ing a density of 34 Beaum^, was used in these tests. Two dilutions were 

 tried, — 1-22, which is about twice the normal strength for application 

 to foliage, and 1-43, which is about the usual dilution for foliage spray- 

 ing. Even at the 1-22 strength this material killed only a comparatively 

 small number of plant lice, and could in no way be considered an effective 

 aphidicide. Furthermore, at this strength there was evident foliage in- 

 jury shortly after application, which took the form of a wilting or droop- 

 ing of the plants. The next day, however, the plants thus injured seemed 

 to have entirely recovered. 



Spraying Apparatus. 



Satisfactory spraying outfits for applying insecticides are equally as 

 important as efficient spray materials. Ordinary hand atomizers are use- 

 less, since it would be necessary to turn over every plant so that the under- 

 side of the leaves could be reached. Such handling would probably result 

 in as much injury to the plants as the plant lice would be likely to inflict. 

 For small garden potato patches, perhaps up to a quarter of an acre, a 

 knapsack or compressed-air spray pump will prove satisfactory. These 

 pumps bold from 3 to 5 gallons of spray, but the frequent need of refilling 

 makes them less desirable for use where larger areas are to be treated. 

 In spraying operations involving fairly large potato fields a barrel pump, 

 traction outfit, power sprayer or similar apparatus will be found the only 

 practicable thing. 



Regardless of the type of pump used, an extension rod and an under- 

 spray nozzle at a right angle to the rod are essential in order that the 

 underside of the leaves may be easily reached. For a knapsack or com- 

 pressed-air pump a 3 or 4 foot extension rod of iron or brass is perhaps 

 most convenient. A 4 or 5 foot length of iron pipe is, perhaps, most satis- 

 factory when directing the spray by hand from a barrel pump, power 



