THE RED SPIDER ON COTTON. 



19 



If infestation has spread until a considerable patch has become 

 involved it is sometimes advisable, in the case of a large field, to plow 

 1113 all the affected portion in order to save the balance of the field. 

 Such a drastic measure, however, should only be resorted to in ex- 

 treme cases, and the planter concerned must be the judge of its 

 advisability. 



Occasional observations of instances wherein infestation had 

 abruptly stopped at a much-traveled road suggested the idea of plow- 

 ing a wide swath just outside the boundary of infestation. This was 

 attempted in one case where the occurrence had covered about 2 

 acres. A 10-foot ring was plowed around the spot, and all stalks, 

 both in the swath and in the inclosed area, were immediately burned. 

 Unfortunately the farmer did not make sure that he was beyond the 

 outermost zone of infestation, and consequently a sufficient number 

 of affected plants remained outside the pulverized barrier to con- 

 tinue, somewhat, the dispersion of the pest. This idea should be 

 given further tests, as it seems there should be great efficacy in the 

 operation, provided the swath is kept stirred frequently. 



Insecticides. — During the season of 1911, 2G spray combinations 

 were thoroughly tested under conditions entirely natural. The field 

 used for this purpose was about 1 acre in extent, and infestation had 

 become both very general and very severe. A strip through the mid- 

 dle of the field, crossing each sprayed plat, was left unsprayed to 

 serve as a check. Since no substance was discovered which could be 

 safely used to destroy all eggs in one application, it was found neces- 

 sary to spray twice, with an interval of six or seven days, so as to de- 

 stroy the hatching larvae. The killing ability of all these sprays was 

 computed, and the percentages ranged from 100 to 0. Each of the 

 following six combinations (see Table IV) was found to be very 

 satisfactory. These are presented to indicate the manner of prepara- 

 tion, together with the cost, of 100 gallons of each. 



Table IV. — Some satisfactory sprays for use iiiiaiust the red spider. 



Sprav 

 No." 



Formula and items. 



Total 

 cost. 



Per cent 

 killed. 



I 

 11 



ni 



IV 

 V 



VI 



Potassium sulphid, 3 pounds, at 25 cents 



Water, 100 gallons. 



Flowers of sulphur, 1 5 pounds, at 4 cents] | 



Fresh lime, 20 pounds, at 4 cents >boiIed< 



Water, 100 gallons I I 



80.60 

 .80 



Miscible oil, 5 gallons, at SI 



Water to make 100 gallons (1 to 20). 



Potassium permanganate, 16i pounds, at 50 cents 



Water to make 100 gallons (2"per cent solution). 



Miscible oil, 2.} gallons, at $1 12. 50 



Blackleaf tobacco extract, 40% nicotine sulphate, 26 ounces, at Si .25 



per pound 2. 00 



Water to make 100 gallons. 



Flowers of sulphur, 28 pounds, at 4 cents $1.12 



Soft soap, 14 ounces, at 40 cents per pound 35 



Water to make 100 gallons. ■ 



1.40 

 5.00 



8.25 



100 



100 

 100 



100 



99 



98 



