The experimental area, located in Marlboro County, was about 5 

 miles wide and extended in a north-south direction along the Great Pee 

 Dee River for about l5 miles. The area was fairly well isolated from 

 other cotton acreages, the nearest plantings being ^ mile to the north, 

 1 mile to the east, and 3 miles to the south and west. 



Procedure.- A treatment schedule was chosen to insure that weevils 

 entering the field from hibernation quarters throughout the entire 

 emergence period would be subjected to a lethal dose of insecticide be- 

 fore oviposition became possible. 



If oviposition is to be prevented during weevil emergence, lethal 

 amounts of an effective insecticide must be continuously present on the 

 plants after they begin to fruit. The residual effectiveness of the 

 insecticides, therefore, must be taken into account when planning the 

 application schedule. The relationship between the preoviposition 

 period, application schedule, and duration of effective residual activity 

 may be expressed as follows: 



I cannot exceed R + P where: 



1 - interval between insecticide applications, 



R = length of effective residual actiArity, and 



P = preoviposition period. 



Thus, assuming a 3-day preoviposition period, an insecticide with 

 less than a U-day effective residual, applied at 7 -day intervals, would 

 be ineffective in preventing oviposition by continuously emerging females. 



It was agreed upon at meetings with the cooperating growers that 

 the early-season applications would be made at 5-day intervals beginning 

 when the oldest cotton in the area (field 2) had developed to the 8-leaf 

 stage. However, it was deemed necessary to initiate the insecticide 

 treatments about 7 days before the plants produced squares because of 

 the evidence in boll weevil-rearing studies that adults can produce 

 viable eggs while feeding on cotton seedlings only (Vanderzant and 

 Davich, 1958). Thus, about 50 percent of the total acreage was treated 

 before the cotton reached the 8-leaf stage. Because of necessary re- 

 planting owing to cool, wet weather, a difference of 3 weeks occurred 

 between the planting of the youngest and oldest cotton in the treatment 

 area. 



Because of the excellent immediate and residual effectiveness of 

 Guthion (0,0-dimethyl S-(I|.-oxo-l,2,3-benzotriazin-3-(i4H)-ylmethyl) 

 phosphorodithioate) , all cooperating growers were asked to use this 

 compound. DDT was included in the later applications to insure control 

 of bollworms ( Heliothis spp . ) . However, one grower chose to use Sevin 

 (1-naphthyl N-methylcarbamate) and BHC-DDT . 



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