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Plenty of Interest in (and Questions About) Insecticidal Seed Treatments

November 6, 2003

When ProShield with Force ST (Syngenta) and Gaucho and Prescribe (Gustafson) were registered for use in the United States, insecticidal seed treatments became alternatives to soil-applied insecticides for control of insect pests of corn. Hopper-box insecticidal seed treatments (such as Agrox DL Plus, Kernel Guard) had been available for control of seedcorn beetles, seedcorn maggots, and wireworms for many years, and many growers used such products to protect corn seeds from early season insect pests. But the new insecticidal seed treatments were applied to the seeds before they were bagged, eliminating the need for growers to apply the seed treatments themselves. In addition, the labels for the newer insecticidal seed treatments included insects that had never appeared on the labels of hopper-box insecticidal seed treatments, including some that feed on corn above ground. Depending on the product and the rate of active ingredient per kernel, these new seed treatments were labeled for control of billbugs, chinch bugs, corn rootworms, flea beetles, and white grubs, as well as for seedcorn maggots and wireworms.

And now we have primarily two insecticidal seed treatments vying for the market--Cruiser (Syngenta) and Poncho (Gustafson). Don't misunderstand; hopper-box insecticidal seed treatments still are available. However, most of the interest in and questions about insecticidal seed treatments these days are focused on Cruiser and Poncho. So the intent of this article is to share with you what we know, and what we don't know, about the performance of these insecticidal seed treatments and their fit in insect management programs.

Following are the rates of active ingredient (a.i.) per kernel for both Cruiser (a.i. is thiamethoxam) and Poncho (a.i. is clothianidin) and the insects that are controlled or suppressed by the respective rates of active ingredient. Although these are the insects listed on the labels, we do not recommend the use of these seed treatments in Illinois for control of all of the insects listed. In fact, some of the insects listed do not threaten corn production in Illinois.

  • Cruiser 5FS (0.125 to 0.8 mg a.i. per kernel)--chinch bug, cutworms (suppression), flea beetles, seedcorn maggot, southern corn leaf beetle, white grubs, wireworms
  • Cruiser 5FS (1.25 mg a.i. per kernel)--billbugs, corn rootworms (light to moderate infestations), cutworms (suppression)
  • Poncho 250 (0.25 mg a.i. per kernel)--chinch bug, corn flea beetle, corn leaf aphid, cutworm (black), grape colaspis, seedcorn maggot, southern corn leaf beetle, southern green stink bug, white grubs (including European chafer larvae, May/June beetle larvae, Japanese beetle larvae), thrips, wireworms
  • Poncho 1250 (1.25 mg a.i. per kernel)--corn rootworms (northern, western, southern, and Mexican), southern corn billbug (note: follow-up foliar sprays of a locally registered insecticide may be needed under heavy pest pressure)

Among the insects listed on the two seed treatment labels, those of greatest concern to most corn growers in Illinois are corn rootworms, cutworms, white grubs, and wireworms. Insects that feed above ground, especially flea beetles and southern corn leaf beetles, also cause concern to some Illinois growers every year. The systemic activity of both thiamethoxam and clothianidin is responsible for control of insects above ground.

So the most important question regarding Cruiser and Poncho is, "Are these insecticidal seed treatments effective against the insects listed on the respective labels?" Considerable data regarding control of corn rootworm larvae with insecticidal seed treatments have been generated. And based on our experience, we state the following in the soon-to-be-published 2004 Illinois Agricultural Pest Management Handbook: "These seed treatments have been evaluated in efficacy trials for several years at the University of Illinois and at other land-grant universities in the Midwest. In general, when rootworm densities and root injury have been moderate, seed treatments have provided acceptable protection of the roots. However, when rootworm densities have been high and root injury has been moderately high to severe, insecticidal seed treatments have not provided consistently acceptable control of corn rootworm larvae. Therefore, we do not recommend their use in fields where the risk of rootworm larval damage is significant." We have ample data to support this statement--for example, the results from our corn rootworm efficacy trials in 2003 ("Root Ratings from 2003 Corn Rootworm Control Trials in Illinois" in issue no. 22, September 5, 2003, of the Bulletin). The Cruiser label indicates control of light to moderate infestations of corn rootworms. However, the Poncho label does not designate the level of rootworm infestation. In fact, the Gustafson LLC Web site proclaims that "Poncho 1250 delivers rootworm control comparable to traditional soil-applied insecticides." Although this statement is somewhat vague and some data can be selected to support it, there are plenty of university-generated data that would not support it.

We repeat the question--"Are these insecticidal seed treatments effective against the insects listed on the respective labels?"--regarding control of insects other than corn rootworms. As we have stated before, efficacy data for control of insects such as white grubs and wireworms are few and far between. And efficacy data for control of most of the other insects listed on the seed treatment labels are even more scarce. We and many of you have been bombarded with yield data, but more often than not, these data are not accompanied by any data associated with insect presence or injury caused by insects. We don't suggest that either Cruiser or Poncho will not control secondary insect pests of corn; we merely point out that there are few data to support the claims for control.

The bottom line of this discourse is relatively simple: Each grower must ask whether an insecticidal seed treatment is necessary. After all, the grower has to pay for the product. And most people know that the seed of all Yield-Gard Rootworm corn hybrids will be treated with an insecticidal seed treatment; growers don't even have the option of purchasing YieldGard Rootworm corn seed not so treated. So growers will have to pay for both the Bt technology and the seed treatment. Is the added expense necessary? Do growers really need to apply insecticides to lots of corn acres for control of insects that may not be present? In some respects, we are returning to the days of using soil insecticides such as chlorinated hydrocarbons without knowledge of the presence of insects. What has happened with the IPM approach?

We pose the questions in the previous paragraph as a focus for current and future discussion. We invite your opinions and welcome the dialogue.--Kevin Steffey, Mike Gray, and Kelly Cook

Author: Mike Gray Kevin Steffey Kelly Cook

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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