No. 1 Article 3/March 25, 2011

Refuge Confusion and Compliance Remain Key Concerns for 2011

The use of transgenic corn remained very high across Illinois and the United States during the 2010 growing season (Figure 1), reaching 82% and 86% of all planted corn acres, respectively. Since 2000, the use of transgenic corn has increased at a very steady rate and has become the dominant production input, fundamentally reshaping how producers manage insects and weeds. Although seed prices, along with other input costs, have risen steadily in the last decade and remain a concern, the current favorable commodity prices will continue to fuel the reliance on transgenic crops for the foreseeable future. Unless widespread resistance to Bt corn by an insect pest develops, demand should remain high for transgenic hybrids that increasingly offer broad-spectrum protection against lepidopteran pests and corn rootworms.


Figure 1. USDA Economic Research Service estimates of genetically engineered corn plantings for Illinois and the United States, 2000 to 2010.

The use of so-called "stacked" transgenic corn hybrids has increased significantly since 2006 for Illinois and the United States, reaching 52% and 47%, respectively, of planted corn acres in 2010 (Figure 2). However, for Illinois the percentage of corn acres planted to stacked hybrids decreased by 7% from 2009 to 2010. Reasons for the decline are probably related to several factors, including low pest pressure the past few seasons and concerns over rising seed costs. I suspect the Illinois decline will eventually be reversed and that the use of pyramided Bt products will dominate in the marketplace. To be clear, note that there is a difference between the terms "stacked" and "pyramided." According to the United States EPA, pyramided Bt hybrids are "products containing two or more toxins efficacious against the same pest." The toxins (Cry proteins) should have "distinct, non-cross reacting modes of action." Stacked Bt hybrids are "products combining toxins efficacious against different pests."


Figure 2. USDA Economic Research Service estimates of stacked gene varieties for Illinois and the United States, 2000 to 2010.

At the 2011 Corn and Soybean Classics, held in January, I queried participants about their use of Bt hybrids. To assure anonymity, responses were provided using the handheld clickers developed by Turning Technologies. The meetings were held in Bloomington, Champaign, Malta, Moline, Mt. Vernon, Quincy, and Springfield. When asked if they planted a Bt hybrid in 2010, on average well over 90% of respondents said yes (Figure 3).


Figure 3. Answers at the 2011 University of Illinois Corn and Soybean Classics to the question "Did you plant a Bt hybrid in 2010?"

On average, across the seven locations, nearly 94% of respondents said they planned to use a Bt hybrid in 2011 as well (Figure 4). This impressive level of use is occurring despite very low pest pressure the past few seasons. The low number of European corn borers across the Midwest has been well documented; however, during the last two years, western corn rootworm densities have been exceedingly low as well. The dearth of western corn rootworms is most likely due to saturated soil conditions during larval hatch (late May, early June) in 2009 and 2010 across many areas of Illinois. However, the decline in numbers is also linked to increasing use of Bt hybrids and widespread applications of pyrethroid insecticides tank-mixed with fungicides to corn and soybean acres in recent growing seasons. The three factors have resulted in a population suppression of western corn rootworms and have left many entomologists wondering if densities of this once perennial pest will rebound in the near future.


Figure 4. Answers at the 2011 University of Illinois Corn and Soybean Classics to the question "Do you intend to use a Bt hybrid in 2011?"

Due to the diversity of Bt hybrids and differing refuge requirements, there is concern that refuge compliance will continue to erode as confusion and ambivalence increase. Slightly more than 20% of producers at the 2011 Classics indicated they did not establish a refuge according to the recommended guidelines (Figure 5). As refuge compliance decreases, we should anticipate increasing selection pressure on pest populations and their eventual adaptation to Bt hybrids. This would be a significant loss and helps to explain why the United States EPA is interested in moving forward with the use of seed mixtures as a refuge strategy for some Bt products--it ensures compliance.


Figure 5. Answers at the 2011 University of Illinois Corn and Soybean Classics to the question "If you planted a Bt hybrid in 2010, did you establish a refuge according to the recommended guidelines?"

In 2011, the dominant resistant management strategy will continue to be the 20% structured refuge approach for most Bt hybrids. On average, nearly 66% of producers indicated they will use this refuge deployment with their Bt hybrids (Figure 6). In Malta, located in northern Illinois, over 20% of growers indicated they will utilize a seed mixture as their refuge. As I noted previously, as more pyramided Bt hybrids enter the market, this will become the dominant refuge management practice. In essence, we will see a 95% to 5% agricultural landscape emerge, with Bt and non-Bt seed interspersed in cornfields.


Figure 6. Answers at the 2011 University of Illinois Corn and Soybean Classics to the question "If [you did plant a Bt hybrid in 2010 and establish a refuge according to the recommended guidelines], which statement best describes your refuge approach for 2011?"

I look forward to writing articles for the Bulletin throughout 2011. Each growing season is unique and typically has its own surprises; I suspect this one will provide some interesting twists and turns. From time to time, please send me your observations from the field so I can share these reports with our readers. I wish everyone a productive 2011.--Mike Gray

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