The commercial availability of Bt (Bollgard) cotton in 1996 through 2000 has provided us with an opportunity to evaluate the performance and value of this technology on a large-scale under grower conditions.
Two hundred sixty Bollgard fields and 260 ‘conventional’ (pyrethroid-protected fields which were grown in close proximity to the Bollgard fields) were evaluated for late-season 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 0.8 applications and conventional fields 2.60 applications, almost all pyrethroids, during this five year period.
Surprisingly, even with the lower insecticide use, the Bollgard fields sustained only 36 percent as much boll damage from bollworms as did the conventional fields — 1.6 percent versus 4.3 percent. However, stink bug damage to bolls was almost four-fold higher in the Bollgard fields — 3.1 percent versus 0.80 percent.
Fall armyworm (FAW) and European corn borer (ECB) damage was generally light throughout most of North Carolina during 1996 through 2000. 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 — 4.6 percent versus 5.6 percent.
As opposed to small-plot replicated tests which we often manipulate to greatly increase insect attractiveness, survival and damage (late planting, excess nitrogen, 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 its first five years of commercial availability.
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, the 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.
We have seen that adopting Bollgard cotton for late-season insect control has been just about a break-even proposition for the ‘average’ North Carolina producer from 1996 to 2000. The technology fee for Bollgard cotton has been essentially offset by it's lower insecticide and application requirements and lower boll damage.
So, 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 two or three-year history of favorable Official Variety Test (OVT) results, when possible, is very important.
Planting Bollgard varieties (or Bollgard plus Roundup Ready varieties) with little or no North Carolina testing history can be risky.
In 2000, the greater availability of the more expensive ‘stacked’ lines (Bollgard plus Roundup) and the scarcity of Roundup Ready-only varieties, resulted in considerable Bollgard acreage being planted in North Carolina — almost half a million acres.
A number of these genetically-altered varieties have shown lower fiber quality than conventional lines in OVT testing. 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.
In selecting varieties for the coming year, producers should carefully weigh their agronomic characteristics, particularly yield potential yield and fiber quality.