The debate over whether Roundup Ready soybean varieties lag elite varieties in yield hasn't slowed farmers' purchases of the new technology. According to seed company representatives, grower satisfaction with Roundup Ready soybeans is high. Companies are quickly selling out of Roundup Ready varieties and are working hard to bring new varieties to market with added defensive traits. It's projected that more than 20 million acres will be planted to Roundup Ready soybeans in 1998.

"My Roundup Ready beans yielded as good, if not better, than my conventional beans," says Rod Heinrichs, Carleton, NE, farmer. "I'll plant half my soybean acres to Roundup Ready varieties this spring, providing I can get that much seed."

Yield lag vs. yield drag. Industry and university agronomists agree there is no yield drag from the Roundup Ready technology. However, in some geographic areas and varieties, there may be yield lag. What's the difference? Yield drag means that the gene transformation technology used to produce transgenic seeds negatively affects yield. Yield lag means that plant breeders haven't yet had adequate time to insert the Roundup Ready gene into the most elite varieties available. But over time, the yield lag will be eliminated with new varieties, they claim.

Don Schafer, soybean product manager for Pioneer Hi-Bred International, says, "It's a breeding challenge to get the Roundup Ready gene into the most elite germplasm with all the other desired traits. It takes time and effort. The whole industry is working hard to put that package together, but it doesn't happen overnight."

Even agronomists aren't sure which data to believe when it comes to determining whether Roundup Ready soybeans have a yield lag compared to other varieties. "I've seen data showing Roundup Ready varieties yield two to three bushels less than, as good as, and two to three bushels more than standard varieties. It's tough to know what to believe," claims Cenex/ Land O'Lakes technical agronomist Joe Gednalske. "I advise growers to find the best soybean variety first and then consider the herbicide options available."

Know your variety. Bob Hartzler, weed scientist with Iowa State University, speculates that growers who were disappointed with Roundup Ready soybean yield performance in 1997 may not have evaluated the varieties closely.

"We encourage growers not to get hung up on a single trait. They need to determine their most yield-limiting factor in growing soybeans. If that's soybean cyst nematodes, they need to choose a variety with SCN resistance," says Pioneer's Schafer. "With the frenzy over Roundup Ready soybeans, some growers may have chosen a variety without the defensive package or the maturity they needed simply because they wanted to plant a Roundup Ready variety."

Karen Marshall, spokesperson for Monsanto, agrees: "Our grower survey shows a significant number of farmers who normally plant Group I maturity soybeans tried Roundup Ready beans in 1997. Well, there weren't many varieties to choose from in that maturity. Some farmers made a trade-off, choosing weed control over varietal fit," she says. "The good news is that more than 300 new Roundup Ready soybean varieties are available for 1998, more than double what was offered last year."

Schafer notes that if there isn't a Roundup Ready variety that fits your agronomic needs, traditional herbicide programs are still excellent options for keeping fields clean.

According to Hartzler, the cost of a traditional herbicide program is close to that of the Roundup program if youhave to apply Roundup twice and factor in the seed technology fee.

Jim Renz, Urbana, IN, prefers planting STS soybeans. (STS is a DuPont herbicide/seed-tolerant system.) "I'll plant more STS varieties this spring. My STS herbicide program costs about $12 per acre. That's about half of what it would cost to purchase Roundup Ready varieties and apply a two-quart rate of Roundup," he says.

Yield results vary. In University of Wisconsin trials, the average yield for 21 Roundup Ready varieties was 59 bu./acre, exactly the same as the trial average for 125 conventional varieties in an adjacent trial. But, if you look at the leader varieties from both trials (those not statistically different from the variety that topped each trial), the average yield of the leading conventional varieties was 3 bu./acre higher than the best Roundup Ready varieties, notes Ed Oplinger, extension soybean agronomist.

Harry Minor, state extension specialist for variety testing with the University of Missouri, tested 43 Group III and 23 Group IV Roundup Ready soybean varieties in central Missouri last year. The best Roundup Ready varieties had yields comparable to those of three high-yielding conventional check varieties. "Based on our tests, any yield lag in these maturities is very small," says Minor.

Interestingly, Dupont Ag Products has published data from Minor's Missouri State Yield Trials showing that Roundup Ready varieties yielded 3.3 bu./acre less than conventional soybean varieties in trials at Columbia, Grand Pass and Palmyra. "The conventional varieties in those trials were three high-yielding check varieties that typically yield 6 to 8% (about 3 bu./acre) more than the average conventional varieties," says Minor. "So the average yield of all Roundup Ready varieties was similar to what conventional varieties yield on average."

Lack of yield data. "Unfortunately, a 3 bu. yield lag may be the real world for farmers," admits Minor. "There is so little yield information available to them (because companies have been slow to enter RR beans in state yield trials) that they're basically selecting Roundup Ready varieties at random and won't end up with the best ones. Once companies regularly enter Roundup Ready varieties in state yield trials, growers can choose the best Roundup Ready varieties just like they choose the best conventional varieties."

Minnesota tested only four RR varieties in 1997. They averaged 54.2 bu./acre, compared to 56.7 bu./acre for all conventional varieties and 56.4 bu./acre for STS varieties. "With so few varieties, it's not a large enough sample to make a definitive statement on performance," says Jim Orf, University of Minnesota soybean breeder.

Continued improvement. "In general, Roundup Ready varieties performed well in 1997, and performance will continue to improve as companies release new varieties," says Mark Schmidt, soybean product manager for Novartis Seeds. "The demand for these products is way ahead of the industry's ability to bring varieties with every defensive trait needed in every situation. We sell 60 soybean varieties in all." He notes that 16 Roundup Ready varieties represent almost half the company's total soybean sales, indicating the intense interest.