ARSENITE OF ZINC AGAINST POTATO BEETLE. 



55 



Table III. — Yields of potatoes from one row from each of Plats I, II, III, and IV, 



sprayed as indicated in Table I. 



One 

 row 

 from 

 plat 

 No. 



Insecticide used. 



Number 

 of plants 

 in row. 



Weight 

 of No. 1 



potatoes. 1 



Weight 

 of No. 2 

 potatoes. 2 



I 



Lime-sulphur and arsenate of lead 



384 

 368 

 385 

 374 



Pounds. 

 188i 

 172?- 

 128 

 143| 



Pounds. 

 25 1 



II 



Arsenate of lead 



26 



III 



Lead chromate 



191 



IV 



Arsenite of zinc 



18 









Excellent to good. 



2 Fair to indifferent. 



By taking the yield of the same number of plants from each row the 

 contrast between the different rows will be more marked. Table IV 

 represents the yield of 374 plants from each row: 



Table IV. — Yields of potatoes from 374 plants from one row from each of Plats I, II, 

 III, and IV, sprayed as indicated in Table I. 



One 

 row 

 from 

 plat 

 No. 



/ 

 Insecticide used. 



Number 

 of plants 

 in row. 



Weight 



of No. 1 



potatoes. 1 



Weight 



of No. 2 



potatoes. 2 



I 



Lime-sulphur and arsenate of lead 



374 

 374 

 374 

 374 



Pounds. 

 183.26 

 175. 401 

 124. 168 

 143.5 



Pounds. 

 25.05 



II 



Arsenate of lead 



26.18 



III 



Lead chromate 



19.07 



IV 



Arsenite of zinc 



18 











i Excellent to good. 



2 Fair to indi 



rferent. 







SPRAYING EXPERIMENTS WITH ARSENITE OF ZINC AT VARIOUS 



STRENGTHS. 



An experiment with the three following strengths of arsenite of 

 zinc in controlling the Colorado potato beetle was begun at the Vir- 

 ginia Truck Experiment Station, Norfolk, Va., on May 31, 1911. 



No. I, arsenite of zinc, 1 pound to 50 gallons of water. 

 No. II, arsenite of zinc, 1^ pounds to 50 gallons of water. 

 No. Ill, arsenite of zinc, 2 pounds to 50 gallons of water. 



On the day the spraying was done (May 31) the rows sprayed with 

 No. I, No. II, and No. Ill had 47, 86, and 88 infested plants, respec- 

 tively. 



On June 2 the row treated with No. I had 33 infested plants, a 

 decreased infestation of 14 plants, or 29.8 per cent. The row treated 

 with No. II had 57 infested plants, a decreased infestation of 29 

 plants, or 33.7 per cent, while the row treated with No. Ill had 38 

 infested plants, a decreased infestation of 50 plants, or 56.8 per cent. 



