Bollgard Cotton Performance Expectations for North Carolina Producers in 1998

Jack S. Bacheler, Extension Entomologist

North Carolina State University

The Planting of Bt (Bollgard) cotton in 1996 and 1997, although limited to only 3% of North Carolina=s total cotton acreage, provided an opportunity to evaluate the performance of this new technology on a large scale under grower conditions. Two hundred thirty two Bollgard fields (NuCOTN 33b) and 232 `conventional´ (pyrethroid-protected fields which were grown in close proximity to the Bollgard fields) were evaluated for boll damage. 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 taken in 21 cotton-producing counties throughout the state.

The Bollgard fields sustained less than 40% as much boll damage from bollworms as did the conventional fields - 1.66% vs. 4.19% (Table 1). However, stink bug damage was approximately 4-fold higher in the Bollgard fields, 2.63% vs. 0.64%. Fall armyworm (FAW) and European corn borer (ECB) damage was generally light throughout most of North Carolina in 1996 and 1997. However, previous research had confirmed that Bollgard cotton was extremely effective against ECB. Somewhat surprisingly, FAW damaged bolls in the Bollgard cotton were only 42% of the levels found in the more heavily-treated conventional cotton. Total boll damage was slightly less in the Bollgard cotton- 4.51% vs. 5.57%.

The conventionally-protected cotton required approximately 2.5 applications for late-season caterpillars (few pests outside of thrips were treated early with foliar insecticides in 1996 and 1997). The Bollgard cotton required no treatments on about half of the fields evaluated, for an average of 0.53%; almost all of the remaining acreage required 1 application (about 1.5% was treated 2 times).

The challenge of late-season insect pressure to Bollgard cotton in 1996 and 1997 was moderate to high. Bollworm and stink bug damage (our major species which can become established on Bollgard cotton) were higher in conventional cotton in 1996 and 1997 than the average of the past 11 years (Table 1). Additionally, tobacco budworms and ECB, two species that are far more easily controlled in Bollgard cotton than in conventionally-protected varieties, were present at exceptionally low levels during the past two growing seasons.

For the average North Carolina cotton producer, the economic returns for insect control slightly favor the continued planting of conventional varieties in most situations. Using a figure of $9.50 per application (pyrethroid plus application cost), conventional cotton, with its average requirement of 2.5 applications annually, has cost the average NC producer just under $25.00 per acre over the past five years (this figure does not include thrips control or the modest fee for the Boll Weevil Containment Program, costs common to both Bollgard and conventional cotton). With the $32.00/acre Bollgard technology fee (less than this in 1998 with lower seeding rates), about $1.30/acre more in seed costs, $5.04/acre insecticide costs ($9.50 x 0.53 applications) minus $7.56 for lighter average boll damage, a rough estimate of the average adjusted expenses (adjusted for the lower boll damage in Bollgard cotton) incurred with Bollgard cotton is about $31.00/acre range. This slightly higher cost for insect control in Bollgard cotton does not include the extra cost associated with scouting Bollgard cotton more intensively.

However, based on seed already sold, Bollgard cotton appears to be carving out an increasing larger 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 would likely pay off. Additionally, where treatment thresholds have been met and insecticides applied to Bollgard cotton, caterpillar control and resulting yields appear in many cases to exceed what is possible in conventional cotton. This opportunately has not yet been fully realized by many of our producers.

Although past and present research here has focused on various aspects of managing Bollgard cotton (scouting procedures, the role of beneficial insects, disruptive sprays, thresholds, resistance management, varietal competitiveness and other areas), much more must be learned about the above to better judge Bollgard cotton=s potential fit in this region. While admittedly more expensive in most situations, Bollgard cotton provided at least as good, and typically somewhat better, overall control of late-season insects (caterpillars and stink bugs combined), than did pyrethriod-protected conventional cotton on most farms in North Carolina in 1996 and 1997.

Table 1. Damaged Boll Survey, North Carolina, 1996-1997: Conventional vs. Bollgard Cotton

^*Conventional fields treated an average of 2.5 times with pyrethroid.