POTATO PLANT LICE AND THEIR CONTROL. 139 



August, when the infestation is more hkcly to be progressive than other- 

 wise. This is especially the case with the average garden potato patch. 

 Over larger areas the practicability of appljdng treatment must be deter- 

 mined by the severity of the infestation, its seasonal importance, — that 

 is, whether it is Uable to be progressive or is past the dangerous stage, — 

 accessibility, available apparatus, etc. 



Reference has already been made to the fact that the winter is passed 

 in the egg stage of the plant louse upon such plants as buckwheat, shep- 

 herd's purse and possibly various other weeds. On this account "clean 

 culture;" the destruction by burning of potato vines, weeds and other 

 refuse about gardens and potato fields after harvest, 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 worthy of more general practice. 



The increased danger to the potato crop from "blight" after infesta- 

 tion with potato lice has already been pointed out. This should em- 

 phasize the need of frequent spraying with Bordeaux mixture or similar 

 fungicide for the remainder of the growing season. 



Ejjicienqj of Various Contact Insecticides for the Control of Potato Lice. 



During the early part of July, when injury by potato lice began to 

 cause considerable apprehension, many conflicting reports were received 

 concerning the efficiency of different contact insecticides recommended for 

 the control of these insects. On this account, as well as from the fact 

 that the demand at this time for nicotine sprays so exceeded the supply 

 in many localities that it was impossible to obtain this material, it was 

 thought desirable to have at hand some more definite knowledge con- 

 cerning the effectiveness of the various common contact sprays, in order 

 to be better able to recommend a substitute where any material desired 

 was unobtainable. 



With this end in view a badly infested potato field, already showing 

 severe injury to the tops, due to the sucking of the plant lice, was selected 

 to carry out these trials, which were conducted by Mr. A. I. Bourne of 

 the Massachusetts Agricultural Experiment Station staff and the writer. 

 All plants treated were thoroughly drenched, the under and upper sides of 

 the foUage ahke, and carefully tagged, check plants being left for com- 

 parisons. It must be kept in mind that a satisfactory contact insecticide 

 combines safety and efficiency with reasonable cost. It must be strong 

 enough to kill the insects and yet not injure the foliage of the plant to 

 which it is applied, and the cost of application must not be excessive. It 

 will be seen from the following report on these experiments that only a 

 comparatively few dilutions of the materials tried met this test. It was 

 impossible, in most cases, to make a very accurate estimate of the per- 

 centage of plant Hce killed, so that where a percentage estimate is given 

 it is intended to show the comparative efficiency of the various insecti- 

 cides tried, and is at best only roughly approximate. It is hardly to be 



