2000 Bollgard Cotton Performance Expectations for North Carolina Producers

Jack S. Bacheler, Extension Entomologist
North Carolina State University
(CCN - 00 - 3d  March 2000)

Bollgard Performance: The commercial availability of Bt (Bollgard) cotton in 1996 through 1999 has provided us with an opportunity to evaluate the performance of this technology on a large-scale under grower conditions. Three hundred sixty Bollgard fields and 360 `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 throughout the state's major cotton production areas. The Bollgard cotton fields averaged 0.75 applications and conventional fields 2.53 applications, almost all pyrethroids, during this 4-year period.

The Bollgard fields sustained only 41% as much boll damage from bollworms as did the conventional fields - 1.61% vs. 3.93% (Table 1). However, stink bug damage to bolls was approximately 4-fold higher in the Bollgard fields, 2.58% vs. 0.61%. Fall armyworm (FAW) and European corn borer (ECB) damage was generally light throughout most of North Carolina during 1996 through 1999. Previous research had confirmed that Bollgard cotton was extremely effective against ECB. Somewhat surprisingly, FAW damaged bolls in the Bollgard cotton were just over half of the levels found in the more heavily-treated conventional cotton, perhaps a result of greater levels of beneficial insects in the less-treated Bollgard fields (Bollgard cotton has little resistance to fall armyworms). Total boll damage from all pests combined was slightly less in the Bollgard cotton- 4.47% vs. 5.25%.

As opposed to small-plot replicated tests which we often manipulate to greatly increase insect attractiveness, survival and damage (late planting, excess N, disruptive over sprays, irrigation, etc.), late-season insect damage on Bollgard cotton has been relatively low in the hands of North Carolina's cotton producers in it's first 4 years of commercial availability.

Table 1. Damaged Boll Survey: Conventional vs. Bollgard Cotton under grower conditions, 1996 to 1999.

^a Conventional fields treated an average of 2.53 times, primarily with pyrethroids.
^b Bollgard fields treated an average of 0.75 times, primarily with pyrethroids.

Economic Comparisons: In Table 2, insect control cost comparisons between Bollgard and conventional cotton are given. Interestingly, when one takes the average projected Bollgard technology fee, insecticide and application costs, differences in late season damage and increased scouting costs for Bollgard cotton into consideration, overall average projected costs and returns for the two systems are nearly identical. Individual producer costs would likely need to be adjusted to account for their particular situations.

Table 2. Average Projected 2000 Insect Control Costs and Damage ($/Acre) of Bollgard vs. Conventional Cotton for North Carolina Producers:

^a Technology fee varies according to seed rate and row spacing.
^b Pyrethroid = $5.50/acre; application = $2.00/acre.
^c Damage: Value of the difference in damage shown in bold.- 1% boll damage equals approx.12 lb. lint/acre; Cotton = $0.65/lb.
^d Scouting requirements for Bollgard typically exceed those needed for conventional cotton.

As you can see from Table 2, adopting Bollgard cotton for late season insect control has been just about a break even proposition for the 'average' North Carolina cotton producer from 1996 to 1999. The technology for Bollgard cotton has been essentially offset by it's lower insecticide and application requirements and lower boll damage.

Advice: With the overall insect-related costs and returns of the two systems so close, the importance of varietal selection, especially choosing those varieties with a 2 or 3-year history of favorable Official Variety Test results, when possible, is every important. Planting Bollgard (or stacked- Bollgard plus Roundup Ready) varieties with little or no North Carolina testing history can be risky. A scarcity of preferred varieties and generally fair to poor seed quality has made varietal selection decisions difficult this spring. Logic argues in favor of planting a number of different varieties to minimize the potential of one variety performing poorly over a significant part of a producer's acreage.

The above information suggests that bollworm management with Bollgard (and Bollgard plus Roundup Ready) cotton is cost competitive with conventionally-protected cotton in North Carolina, although shifts toward higher stink bug, and sometimes plant bug) levels can be expected. Future articles will address the differences in managing insects in these two technologies.