54 



PAPEES ON»INSECTS AFFECTING VEGETABLES. 



On the day following the second application of the sprays a count 

 of the infested plants in each plat was made and the following figures 

 obtained: 



Table II. — Results of spray applications against the Colorado potato beetle, Norfolk, 



Va., May, 1911. 



Plat 

 No. 



Insecticide used. 



Number 



Number 



of in- 



of unin- 



fested 



fested 



plants. 



plants. 



37 



347 



118 



622 



216 



169 



206 



1,048 



152 



741 



225 



555 



Infesta- 

 tion. 



I 



II 

 III 



IV 



V 



VI 



Lime-sulphur (2-50 formula) and 3 pounds of arsenate of lead 



Arsenate of lead, 3 pounds to 50 gallons of water 



Lead chromate, 2 ounces to 4 gallons of water, and 1 ounce to 1 gal 



Ion of water 



Arsenite of zinc, 1 \ pounds to 50 gallons of water 



Bordeaux mixture (4-6-50 formula) and 1 \ pounds Paris green 

 Bordeaux mixture (4-6-50 formula) and \\ pounds arsenite of zinc. . 



Per cent. 

 9.6 

 15.9 



+56.0 

 16.4 



+17.0 

 28.8 



It will be seen that the results obtained from the use of lead 

 chromate were very unsatisfactory as compared with those in the 

 case of other insecticides used. The lead chromate employed was in 

 the form of a powder, and great difficulty was experienced in making 

 it mix well with water, it having a tendency to settle quite rapidly, 

 requiring constant agitation to keep it in solution. It adhered well 

 to the foliage, and its color stood out quite prominently in contrast 

 to the other plats. However, the young larvae seemed to be able to 

 feed on plants that were thoroughly covered with the material without 

 receiving much injury. 



The arsenite of zinc employed was also in the powdered form. It is 

 much lighter than lead chromate and remains in suspension in water 

 much better. It adheres to the foliage very well and does not, so far 

 as could be observed, burn or injure the plants in any way. 



The percentage of infested plants in the plat that was treated 

 with Bordeaux mixture and arsenite of zinc was somewhat greater 

 than in the plat in which the arsenite of zinc alone had been used. 

 This was no doubt due partly to the fact that the Bordeaux-arsenite 

 of zinc plat was in a different field, one which had been in potatoes the 

 previous year and was thus subject to the attack of a greater number 

 of beetles. Also, many of the plants which were counted as infested 

 were only slightly injured, and it is doubtful if the yield of potatoes 

 would have been much lessened. ♦ 



On June 29 the potatoes were dug, and following are the weights 

 of one row of potatoes in each of the first four plats. 



