Cotton Notes

Bollgard Cotton Strong in 1996 North Carolina Debut

Jack S. Bacheler - Extension Entomology Specialist

The introduction of Bt (Bollgard) cotton in 1996 provided an opportunity to evaluate the insect control performance of this new technology on a large scale in North Carolina under grower conditions. As part of an annual damaged boll survey, 116 Bollgard fields (NuCOTN 33b) and 116 'conventional-paired' (pyrethroid-protected fields which were grown in close proximity to the Bollgard fields) were assessed. One hundred bolls from each field were randomly-selected and evaluated for bollworm, European corn borer, fall armyworm and stink bug damage. These assessments were undertaken in 21 cotton-producing counties throughout the state.

Somewhat surprisingly, the Bollgard fields sustained less than half as much boll damage from bollworms as did the conventional fields- 2.33% vs. 5.58% (Table 1). However, stink bug damage was approximately 4-fold higher in the Bollgard fields compared with the conventionally-protected fields, 3.03% vs. 0.75%. Fall armyworm (FAW) and European corn borer (ECB) damage was extremely light throughout North Carolina in 1996; however, previous research here has shown Bollgard cotton to be weak against FAW and very effective against ECB, with ECB being far and away a more significant cotton pest in North Carolina than FAW in most years. Overall boll damage was about even for the contrasting technologies.

The conventionally-protected Bollgard cotton required just over 3 applications for late-season caterpillars (essentially no other pests were treated with foliar insecticides in 1996). The Bollgard cotton required no treatments on 42%, one treatment on 55% and two treatments on 3% of the acreage, for an average of 0.61 treatments per acre.

All in all, the insect challenge for Bollgard cotton was somewhat higher than average in North Carolina in 1996. Bollworm and stink bug damage (both species can become established on Bollgard cotton) were higher in conventional cotton in 1996 than the average of the past 11 years (our damaged boll survey was begun in 1985)(Table 1). Additionally, tobacco budworms and ECB, two species which are far more easily controlled in Bollgard cotton compared with conventionally-protected varieties, were present at exceptionally low levels during the last growing season.

For the average North Carolina cotton producer, the economic returns still favor the continued planting of conventional varieties throughout most of the state, except in special circumstances. Using a figure of $9.50 per application (pyrethroid plus application cost), conventional cotton, with its average requirement of 3 applications annually, has cost the average NC producer approximately $28.50 per acre over the past 5 years. With the $32.00/acre Bollgard technology fee, about $1.30/acre more in seed costs, and $6.65/acre insecticide costs ($9.50 x 0.61 applications), a rough estimate of the average expenses incurred with Bollgard cotton is in the $40.00/acre range. This higher level does not include the extra cost associated with scouting Bollgard cotton more intensively.

However, Bollgard cotton still appears to be carving out a small niche in this state's cotton culture. Areas of higher caterpillar pressure (4 to 6 applications/acre/year, or where ECB's are a traditional problem), fields in environmentally-sensitive areas (near ponds or other aquatic systems, schools, hospitals, etc.), and remote fields where extra travel and other expenses are required to treat these areas are situations in which utilizing Bollgard technology may pay off. Although past and present research here has and will be focused on various aspects of managing Bollgard cotton (scouting procedures, the role of beneficial insects, thresholds, resistance management, varietal competitiveness and other areas), much needs to be learned about its potential fit. While admittedly more expensive in most situations, the performance of Bollgard cotton was at least as good, and typically somewhat better, than conventional caterpillar control on most farms in North Carolina in 1996.

Hopefully, a more equitable, variably-priced technology assessment structure, based on the value of this technology in areas of lower caterpillar control costs (such as the Carolinas and Virginia), will make transgenic Bt cotton more affordable to producers in this region. In the meantime, conventional varieties protected selectively with insecticides for late-season caterpillars continue of offer North Carolina producers an effective option for inexpensively managing late-season insects.

Bollgard cotton accounted for about 2.8% or 20,000 of this state's 719,000 acres in 1996. An increase of about 25% in Bollgard-planted acreage is expected this year.

Table 1.  Damaged Boll Survey, North Carolina, 1966: 
          Conventional vs. Bollgard Cotton                        

Mean Percent Damaged Bolls

Europ. Boll- Corn Fall Stink Total Category worm Borer Armyworm Bug Damage
Historical 3.91 1.69 0.47 0.58 6.65 Ave.: 1985-1995 (n = 2217 Fields) 1996 Conventional* 4.44 0.30 0.09 0.75 5.58 (n = 116 Fields 1996 Bollgard ** 2.30 0.03 0.06 3.03 5.41 (n = 116 Fields) * Conventional fields treated an average of 3.03 times with pyrethroid ** Bollgard fields treated an average of 0.61 times with pyrethroid

Back to the 1997 and earlier Cotton Notes

Carolina Cotton Notes CCN-97-4a April, 1997

Cotton Team