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Issue No. 22, Article 2/September 2, 2004

2004 Evaluations of Rootworm Control Products

For many growers, 2004 has been a bumper-crop year for corn rootworms, and it was no different in our rootworm-control efficacy trials. Each year, we establish three trials at University of Illinois research and education centers near Urbana, Monmouth, and DeKalb. We plant our rootworm-control trials into areas in which a "trap crop" (late-planted, mixed-maturity corn hybrids + pumpkins) was planted the previous year. The trap crop attracts egg-laying female rootworms. Consequently, we usually have considerable rootworm pressure in our trials.

We planted all of our rootworm-control trials in mid- to late April (Urbana, April 19; Monmouth, April 27; DeKalb, April 28). Two corn hybrids were used in each of these trials, Golden Harvest H-8588RW (YGRW) and Golden Harvest H-8799 (nontransgenic isoline). Each treatment plot was four rows wide and was replicated four times in a randomized complete block design. Table 1 shows the average root ratings from our rootworm-control trials at the three locations. These averages are based on 20 roots (five from each replication). The roots were rated on the 1-to-6 scale developed by Hills and Peters (1971). A brief video describing the rating scale can be found on the IPM Web site.

Because of the abundance of rootworm larvae, injury in our untreated check plots was severe, resulting in high average root ratings (5.00 at DeKalb, 5.75 at Monmouth, and 5.80 at Urbana). The economic index used by many entomologists is a root rating of 3.0 (several roots eaten off to within 1-1/2 inches of the plant but never the equivalent of an entire node). Rootworm damage resulting in a root rating above this index could lead to potential yield loss and be deemed unacceptable. That said, the average root ratings in the untreated checks well exceeded this threshold, as did the average root ratings for some rootworm-control products.

The performance of the rootworm-control products varied not only by location but also by type (liquid, granular, transgenic) and formulation. Consequently, it is difficult to make many generalities about performance of products, with the exception of a few products. Empower2 did not perform well under the intense pressure at Urbana or DeKalb, with average root ratings above 4.0 at both locations. Likewise, the seed treatments could not withstand the high pressure at any of the three locations. The Cruiser and Poncho treatments had average root ratings ranging from 4.15 to 5.10 and 3.95 to 4.10, respectively. In regard to liquid insecticides, Lorsban 4E provided significantly better root protection than Capture 2EC at Urbana and DeKalb. YieldGard Rootworm (YGRW) transgenic hybrids had the lowest average root ratings at Monmouth (1.80) and DeKalb (2.35). However, the average root rating for YGRW corn was higher than the average root ratings in plots treated with some traditional insecticides at Urbana. We had not encountered an average root rating greater than 3.0 for YGRW corn in previous years' efficacy trials, so the average root rating of 3.15 for YGRW at Urbana raised more than one eyebrow. This topic is addressed in another article in this issue of the Bulletin, "Transgenic Corn Hybrid Stumbles in Urbana Experiment; Some Producers Also Report Lodging with YieldGard Rootworm Hybrids in Commercial Fields."

In closing, I would like to touch on some questions asked at this year's University of Illinois Crop Sciences Research and Education Center Agronomy Day (August 19). More than one grower asked questions such as "My insecticide didn't work. What should I use next year?" and "Why does product X work in your trials, but it hasn't worked for me or my neighbors in years?" Unfortunately, I don't have definitive answers for those questions. My suggestion is to look at product consistency over time and geography. If our results contradict what you are seeing in your area, consult results from other land-grant universities. If nothing else, ask your neighbors what they are using for rootworm control, how long they have used it, and whether they have been consistently happy with the results. However, I add a word of caution. If you ask a neighbor for advice, inquire whether he or she ever left an untreated check strip to determine what the rootworm pressure really is. If the level of rootworm pressure is unknown, then the true performance of a product is unknown as well.--Ron Estes

Ron Estes

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