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Soybean Weed Control: Clash Of Technologies

An aggressive skirmish between rival herbicide makers for your soybean input dollar is creating a frenzy of pointed debate that's usually reserved for a congressional filibuster.

The most vocal player, American Cyanamid, a longtime soybean herbicide market leader with Pursuit and Scepter, is taking a vigorous stand due to a Roundup Ready (RR) bandwagon that is pushing to cover 20+ million acres. Other companies also have campaigns underway to keep and grow marketshare in light of this popular technology, most noticeably is DuPont's price slashing of Reliance STS and Synchrony STS for herbicide-tolerant STS soybeans, and Classic for all soybeans.

Cyanamid's plan is to prove the need for residual weed control, a practice it says will out-yield a total-post application of Roundup. In the opposing camp, Monsanto continues its aggressive promotion of data that touts the exact opposite - no need for anything but Roundup. And in printed public information, both sides have used the same university research to prove their respective claims.

Who's right? Given wide-ranging variables that transpire each season, university weed scientists say both camps can claim victory in a given trial and given year. Monsanto has staked claim to a 2 bu./acre advantage for total post control in RR beans compared to use of a soil-applied herbicide, based on 330 grower trials.

In Cyanamid's 86 side-by-side grower tests on RR beans, where imidazolinone residual herbicide programs were compared to a single (1 pt./acre) application of Roundup Ultra, the residual programs showed an average yield advantage of 4.7 bu./acre in 1997.

"Based on research over several decades, it's essentially a standoff," says George Kapusta, Southern Illinois University's veteran weed specialist, who's philosophy on this subject mirrors his peers.

"Crops can compete with weeds for about four weeks after planting with little or no yield reduction, as long as farmers who use post products understand the risks of proper application timing, weed spectrum and germination specifics, and a hard-to-predict weather variable - all which can cut yields."

Iowa State agronomist Bob Hartzler agrees. "We can manage weeds with a single pass, and it's somewhat easier today with Roundup Ready beans, but the risks are greater compared to a two-pass program."

A need to scout. For the thousands of growers facing this total post control decision on RR beans (or on any variety), Hartzler says to consider an application window rule-of-thumb to help prevent yield loss when going total post: "If you have low weed populations you can wait up to five weeks after emergence. But with medium to high weed populations, your spray window narrows drastically to between the third and fourth week," he says.

Risk-aversive growers who want insurance against total post can opt for a soil-applied program first. The obvious goal here is, given proper soil moisture, to reduce the weed load and widen the post application window to increase success. But when adding this step, especially into a RR bean program, input costs must be carefully scrutinized. If you're already paying a seed premium and technology fee, does the cost of a specific soil-applied program add to or subtract from the bottom line?

Cyanamid offers a residual protection package to offset the cost of Roundup Ultra used in-crop. According to Brian Nelson, product manager for Pursuit Plus and Steel, if you use soil-applied Pursuit Plus or Steel, Cyanamid will pay up to $7/acre for Roundup if needed. Or, put Prowl down followed by a Pursuit+Roundup tankmix and receive a discount up to $12/acre.

To complicate the buying decision, the list of rebates offered by many companies appear endless. And these programs may vary by dealer and by how many acres you plan to treat, so check with several reliable suppliers. Or perhaps it's time to consider hiring an unbiased, independent crop consultant to help sort things out and reduce risk.

"If a grower calls me and wants a general recommendation for his weed control program, I tell him it's impossible to generalize," says Maggie Jones, a crop consultant with Blue Earth Agronomics, Lake Crystal, MN. "I begin by asking questions and listening to a grower's weed problems, field history, spray equipment, tillage system, labor supply, time constraints and economic situation."

Only then will Jones, an independent certified professional crop consultant (CPCC-I), begin helping growers sift through field-by-field options. "My approach is education; provide sound, unbiased recommendations and let the farmer make the final choice," she says. "The biggest positive (about soybean weed control) is that a grower's choices are better than ever. Roundup Ready beans may be the best program in some fields, but the worst in others. That's why it pays to sort out all the details."

Irregardless of who helps you decide what herbicide inputs to buy, it pays for you to keep up on the latest news and advances to stifle this year's weed crop.

Resistant seed news. Pricing is the biggest news, and RR beans are driving many players in the industry to reevaluate profit margins. Whether it's in the form of direct price reductions, rebates, discounts for buying several of one company's products, or other such programs, it'll pay to shop around and examine the details. Check out the chart on pages 12, 14 and 16 for more details.

In the fast growing herbicide-resistant seed arena, the significant news is 300 new RR soybean varieties. More choices allow growers to buy a better maturity or disease or genetic package, and gain more yield potential. The incorrectly criticized yield drag of RR soybeans is actually yield lag (see story on page 30), defined as the time frame necessary to properly move genes into top genetic lines. "A much broader varietal selection exists this year from more than 90 seed companies, giving growers more disease resistance options and more northern varieties," says Doug Dorsey, Monsanto's soybean market manager.

The company maintains that 75 to 80% of RR soybean growers use only one application. "If growers start with a clean field, then apply 32 ounces of Roundup Ultra when annual weeds reach 4 to 8 in. (in the north-central region), one-pass control will usually succeed," Dorsey says. "It's best to time application based on annual weed size not days after planting."

There are weed exceptions to this rule. The label recommends earlier application (3 to 6 in. tall) on nightshade, smartweed, and morningglories; later application on giant ragweed (8 to 12 in. tall); and higher rates to suppress or control nutsedge and/or perennial weeds.

Obviously, you can't hit the proper timing of all weeds, and waiting too long can jeopardize yields. That's why university weed specialists recommend sequential Roundup applications or the use of a residual herbicide to stifle such tough species and reduce farmers' risks.

And Monsanto's latest program is targeted to reduce a grower's aversion to total post weed control risks. If growers sign up for the company's Technology Value Package and follow application guidelines, they'll receive up to 24 oz./acre of Roundup Ultra should a second flush of annual weeds require a sequential application.

Speaking of value, DuPont's herbicide-tolerant STS soybean program quickly became competitive this fall when the company dropped the price of Synchrony STS and Reliance STS from $15/acre to $4 to $5/acre. "We believe this program is competitive with Roundup Ready in any scenario, from weed spectrum to crop safety to value," says Fran Castle, the company's STS product manager. "It's especially effective when growers use our new Authority First/Synchrony STS, which will cost less than $20/acre for broad-spectrum weed control."

This two-pass co-pak consists of soil-applied Authority followed by Synchrony STS (Classic+Pinnacle) post, targeted to central Midwest growers where nightshade and waterhemp reign king. One buying caution: If soils have a pH of 6.8 or higher, DuPont recommends using Reliance instead of this co-pak in STS beans. Regarding supply, DuPont says 100 seed companies will offer enough STS soybean seed to cover 5 to 7 million acres in 1998.

Liberty herbicide will make its initial soybean appearance on approximately 100,000 acres of resistant beans in 1998. Croplan Genetics (Cenex/Land O'Lakes) is the only supplier this year, offering one mid- to late-Group II Liberty Link variety.

"Just like in Liberty Link corn, Liberty controls over 100 weeds, and can be applied alone at an early- or mid-post application," says Rick Mohan, AgrEvo's marketing manager for soybeans. "And for growers who are not sold on the risks associated with total post weed control, we also recommend a two-pass program with a good grass soil-applied herbicide down, followed by a mid-post application of Liberty," he says.

Over-the-top control. Cyanamid, out to defend its market position, offers a new post herbicide called Raptor, which received approval in late May last year. "Due to registration timing, we were fortunate to get it out on 60,000 acres (mostly mid-post applications) in 1997 and were pleased with performance of Raptor," says George Fennell, Cyanamid product manager.

It is claimed to provide contact control of more than 50 broadleaf weeds and grasses, and deliver three to four weeks residual or more. "We feel Raptor can fit more acres than Pursuit because it doesn't have the residual concerns. And it'll work on taller (up to 5 in.) weeds than Pursuit which widens the grower's application window," Fennell says. "It can be used as a total post program in certain areas, but for optimum control we recommend starting with a soil-applied grass herbicide first, then come back with Raptor at 4 oz./acre on 3 to 4 in. weeds." See chart for details.

Soybean growers battling white mold disease may want to try a herbicide. A unique label for a herbicide, the EPA just approved a 6 oz./acre post application of Cobra applied at or near bloom stage to suppress this yield-robbing disease. "Farmers and custom applicators first noticed disease suppression six or seven years ago, so we began research work with several universities to confirm it," says Kevin Perry, Valent's product development manager for Cobra and Select.

"A Cobra application ($7 to $8/acre) at or near bloom triggers a physiological systemic acquired resistance (SAR) response that can cut disease incidence in half, saving 2 to 10 bu./acre depending on the varietal resistance to white mold," Perry says. "We've also seen suppression with it when applied at the normal weed control timing of two to three weeks after planting, but we lack enough data to put this on the label right now." The other label change for Cobra is a new tankmix with Synchrony or Reliance for use in STS soybeans.

DuPont's Reliance (Classic+Pinnacle) herbicide's new label allows it to be used on regular soybeans, not just STS beans, at a greatly reduced price. "Growers in the northern Midwest used a product called Concert until we dropped it a few years ago, so we're offering them Reliance (similar ratio of Classic and Pinnacle) that does not have to be used on STS beans," says DuPont's Castle.

New soil-applied options. Dow AgroSciences (formerly DowElanco) offers new FirstRate broadleaf herbicide, which is used either as a post or soil application. From the same chemical family as Broadstrike, it is claimed to provide consistent control of cocklebur, common and giant ragweed and sunflower, along with velvetleaf and morningglories, all without concern for crop injury or carryover to follow crops.

"The weed spectrum varies slightly by application," says Brian Barker, product resource manager for Dow AgroSciences. "Both will control the listed weeds, but a soil application of .6 to .75 oz./acre ($14 to $18) goes further by controlling pigweed and lambsquarter. But that treatment is higher than our .3 oz./acre post rate, which costs $7 to $9/acre," he says.

The post application window is fairly wide, sprayed when the average weed height is 4 to 5 in., but can go up to 6 to 8 in. on some species. "The only broadleaf weaknesses are nightshade and waterhemp, which can be eliminated with a tankmix partner," Barker says.

The accompanying three-page chart (see printed article) has more details on these and other products. Note that we've added "site of action" for each herbicide. This is important when determining a weed-resistance strategy, since many experts say to avoid using the same site of action more than two years in a row.

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