Issue No. 1, Article 2/March 16, 2005
Practice Safe S.E.X. (Sensible, Erudite [use of] Xenobiotics) in 2005
Maybe some definitions are in order first: erudite--learned, knowledgeable; xenobiotics--a chemical compound that is foreign to a living organism. We'll stretch the definition of xenobiotics to include proteinaceous materials (e.g., Bt [Bacillus thuringiensis] proteins) in the context of this article. Although the title for this article may be overly cute for your taste, the intent of the message is serious.
For reasons mentioned in the article "What Lies in Store for Us in 2005?" many producers will be on edge about insect management in 2005. At the heart of this anxiety are the rootworm-control problems many producers experienced in 2004 and the potential for a soybean aphid outbreak in 2005. Both of these issues should be a focus of insect management programs for corn and soybeans in 2005, but neither of them should be addressed with knee-jerk reactions.
Control of rootworm larvae with granular and liquid soil insecticide, seed-applied insecticides, and transgenic Bt corn (i.e., YieldGard Rootworm corn) was compromised in many cornfields in 2004, for reasons we have enumerated many times in articles in the Bulletin and during educational meetings this past winter. The reasons for unacceptable performance of rootworm-control products have been discussed thoroughly and frequently. More important, at least for the primary intent of this article, are the potential responses of some producers to their experiences with the use of rootworm-control products that did not meet their expectations last year. One of the most straightforward responses by producers who were not satisfied with the performance of their selected rootworm-control product in 2004 is to use another product in 2005. There's no real reason to question this legitimate decision. However, some of the other overheard "solutions" to the rootworm-control problem cause significant concerns among pest management specialists. The list of "solutions" is lengthy, but a snapshot includes
- increasing the rate of granular or liquid insecticide of choice,
- applying a granular or liquid insecticide to corn treated with a seed-applied insecticide (i.e., Cruiser, Poncho), and
- applying a granular or liquid insecticide to YieldGard Rootworm corn.
We hope that most of you recognize the mostly irrational nature of these "solutions" to the rootworm-control problem.
It's important to emphasize that "the sky is not falling" with reference to rootworm control. It's true that rootworm-control products were challenged significantly in many fields in 2004 by large densities of rootworm larvae. However, most rootworm-control products did exactly what they were expected to do (i.e., protect corn rootworm systems from rootworm larvae) in the vast majority of fields in 2004. Therefore, we see no reason to resort to short-term "solutions" that could result in more significant long-term problems. So our responses to the aforementioned "solutions" are, in order, as follows:
- Increasing the rates of application of soil insecticides almost never has improved performance of granular or liquid insecticides for rootworm control.
- Granular and liquid soil insecticides should control the same suite of insects listed on the Cruiser and Poncho labels, so the use of both is unnecessary.
- Applying a granular or liquid insecticide to YieldGard Rootworm corn exposes the rootworm population to three active ingredients--the chemical active ingredient in the granular or liquid soil insecticide, the nicotinoid active ingredient in Cruiser or Poncho (all YieldGard Rootworm corn is treated with one or the other), and the Bt protein expressed in YieldGard Rootworm corn. In addition, this approach toward rootworm control violates the principles of insect resistance management associated with transgenic corn.
Every one of the aforementioned "solutions" for rootworm control places increased selection pressure on the rootworm population. Given our experience with western corn rootworms' ability to adapt (e.g., resistance to insecticides, the variant western corn rootworm that lays eggs in soybeans and other crops), we sincerely hope that we do not repeat mistakes from which we should have learned harsh lessons.
As for expectations for soybean aphid infestations in 2005, it's true that the potential for an outbreak exists, assuming that captures of soybean aphids in suction traps in the fall is a reliable predictor of infestations the following year. The numbers of soybean aphids captured in suction traps in the fall of 2004 were very high, so the overwintering population likely is high. However, we are not certain whether multicolored Asian lady beetles will have a negative impact on densities of soybean aphids in 2005, nor can we predict the weather. During the 2 years in which we experienced economic infestations of soybean aphids (2001 and 2003), temperatures during the summer were characterized as "cooler than normal." Development of soybean aphid populations slows down when temperatures exceed 85°F, so hot summer temperatures could prevent the development of a wholesale soybean aphid outbreak. Only time will tell.
Nonetheless, some people are preparing already for a soybean aphid outbreak, and some people will be ready to spray insecticides with or without a herbicide (i.e., Roundup) or a fungicide (for prevention or control of soybean rust) at the first sign of soybean aphids. Although we encourage preparedness, we discourage the application of insecticides before soybean aphids have reached the established economic threshold of 250 aphids per plant.
We hope that people use insect-control products rationally (by practicing safe S.E.X., which is not always characterized by spending money) in 2005. We encourage you to keep apprised of pest developments and to scout regularly. There really are no substitutes.--Kevin Steffey, Mike Gray, and Kelly Cook