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Rag1 gene availability
The Rag1 gene is available in more soybean varieties this season.
In Iowa, for example, about a dozen national and regional seed companies are offering 16 unique soybean varieties with aphid resistance, says McCarville, who surveyed 128 seed companies in January. “That’s more than we expected for 2012.”
Available maturities range from 1.2 to 3.0. About half the aphid-resistant varieties available for Iowa and similar maturity zones are Roundup Ready, McCarville says. Additional traits available in some cultivars include SCN resistance and tolerance to phytopthora and brown stem rot.
Monsanto and its regional seed companies are offering several Genuity Roundup Ready 2 Yield varieties with Rag1, in maturities from mid-Group 1 to early-Group 2, with or without Acceleron seed treatment, says Tony White, soybean product manager.
Syngenta offers aphid resistance varieties through the Aphid Management System with NK Brand soybeans. The system combines the Rag1 gene and CruiserMaxx Beans fungicide/insecticide seed treatment. Maturities range from early-Group 1 to mid-Group 2, says Quinn Showalter, soybean traits marketing manager. The company’s Aphid Management System includes a $5/acre assurance for Endigo ZC foliar insecticide if aphid populations exceed economic threshold levels.
Pioneer Hi-Bred has not yet introduced aphid resistance into its commercial lineup, says Don Schafer, senior marketing manager. However, Pioneer rates all its soybean varieties for antibiosis, the plant’s natural ability to reduce aphid growth, survival and reproduction. “Growers can use these ratings to help them determine field scouting priorities and insecticide application decisions.”
Until Rag genes are incorporated into more cultivars, O’Neal says, growers should weigh aphid resistance traits against other yield and agronomic traits. While studies show there is no yield penalty associated with Rag1, the gene “may not yet be in the best-yielding variety for your particular region” or environment, he says.
Bryan Stenzel, Wells, MN, planted 50 bags of NK 2.1 RM soybeans with Rag1 in 2011. Aphid pressure was heavy in his area. The Rag1 variety did a great job of suppressing aphids, Stenzel says, but it didn’t yield as well as his non-resistant beans, lagging by about 6 bu./acre.
If you plant a Rag1 variety this spring, keep in mind that you might still have to spray for aphids.
Although Rag1 lowers the number of aphids on plants, “it won’t always reduce them enough that growers don’t need to apply insecticide,” O’Neal says. “In certain circumstances, aphid numbers could be high enough to cause yield loss. It depends on the weather and aphid genetics.”
Host plant aphid resistance “is not a silver bullet,” agrees Monsanto’s Tony White. “The gene does an excellent job, but farmers still need to scout,” and spray if aphid numbers exceed the recommended threshold of 250 aphids per plant on 80% of plants.
If you plant an aphid-resistant variety, should you add a seed treatment, too?
“We advocate seed treatments to help with early-season aphid control,” White says. The 2011 six-state study found that insecticide seed treatments further curbed aphid numbers on resistant varieties, McCarville says. However, seed treatments did not provide an economic return on the Rag1-and-Rag2 stack.
Seed companies are working to incorporate Rag1 and Rag2 traits into their elite soybean varieties, O’Neal says, and the industry has additional sources and combinations of aphid resistance in the breeding pipeline, including Rag3 and Rag4. “The future is bright for this.”