POTATO PLANT LICE AND THEIR CONTROL. 145 



deaux mixture or arsenate of lead, but soap should be omitted when such 

 combinations are made. These combinations are equally as effective as 

 when the materials are used separately. 



Kerosene emulsion is not highly effective against potato plant lice, and 

 the labor involved in preparing this material is also against its use. 



Tests with miscible or soluble oils seem to indicate that these materials 

 are dangerous to use upon potato foliage. 



Lime-sulfur is ineffective for the control of potato plant lice even at 

 double the ordinary strength used upon foliage. 



2. Satisfactory results with an efficient contact spray can be expected 

 only when thorough work is done. Each insect must be hit with the spray. 

 Since plant lice confine their work almost wholly to the underside of the 

 leaves, the spray must be directed upward from underneath the plants. 

 An angle disk nozzle or similar underspray nozzle is necessary for such 

 work. One thorough application with an efficient spray should control 

 potato plant lice so that a second treatment will be unnecessary. Too 

 much handling or trampling about the plants will often result in more 

 injury than the plant lice are likely to cause. 



3. The practicability of applying treatment for the control of potato 

 lice, especially over large areas, must be determined by the severity of 

 infestation, its seasonal importance, — that is, whether it is likely to be 

 progressive or is diminishing in severity, — accessibility, available appa- 

 ratus, etc. If injury to the plants has not been severe enough to kill por- 

 tions of the tops of the plants to an evident extent before the 1st of 

 August, it is probable that the injury likely to be done will not exceed the 

 cost of applying treatment. When severe injury is noticeable before the 

 1st of August, a thorough treatment should be made at once. Application 

 before the insects are present in numbers will be merely a waste of time 

 and energy. 



4. The destruction by burning of potato vines after harvest, together 

 with all weeds and other refuse about gardens and potato fields, unless 

 such material is composted; the burning over of grassy and weedy fields 

 in the vicinity of potato patches in the late fall or early spring; and late 

 fall plowing of gardens are methods of clean culture which may materially 

 reduce future infestation. 



5. Injury by potato lice renders the plants more susceptible to "blight," 

 and should emphasize the need for frequent sprays with Bordeaux mixture. 



Natural Agents in the Control op Potato Plant Lice. 



Many factors contribute to a natural control of potato lice; in fact, to 

 such an extent that during most seasons in the past their injury has been 

 unimportant in Massachusetts. 



Weather conditions rank very high among controlling influences. Cool 

 or wet weather offers quite a decided check to aphid development, and 

 heavy or continuous rains undoubtedly destroy many of these delicate 

 insects. 



