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Impact of Bollworms on Maturity and Yield Bollgard® and Bollgard II® Cottons

Jeff Gore and J.J. Adamczyk, Jr.


The bollworm, Helicoverpa zea (Boddie), is an important pest of cotton in the United States. Currently, a large percentage of Bollgard® cotton is treated with insecticides to control bollworms with little information about economic losses from these infestations. Also, Bollgard II® cotton was recently commercialized and no information is available about economic injury from bollworms on Bollgard II. The objective of this study was to determine the impact of bollworm infestations on maturity and yield of Bollgard and Bollgard II cottons. Bollworm infestations were established on non-Bollgard, Bollgard, and Bollgard II cottons in large field cages. Treatments included three and five levels of infestation for one to four weeks in 2002 and 2003, respectively. Bollworms significantly delayed maturity and reduced yields of Bollgard cotton when 50 or 100 percent of white flowers were infested for one to four weeks in 2002. In 2003, bollworms delayed maturity of Bollgard cotton when 100 percent of white flowers were infested for four weeks. Yields of Bollgard cotton were reduced when greater than 10 percent of white flowers were infested with bollworms for two to four weeks and when 10 to 100 percent of white flowers were infested for three to four weeks. Bollworm infestations did not delay maturity or reduce yields of Bollgard II cotton. Based on results of this study, insecticide applications targeting bollworms on Bollgard cotton should be initiated before infestation levels reach 10 percent of white flowers. In contrast, Bollgard II cotton was less susceptible to bollworms and is not likely to require insecticide applications as frequently as Bollgard cotton.

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Document last modified 04/27/04