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Finally, A Broadleaf Herbicide for No-Till

Tuesday, February 1, 2000
filed under: Weeds

Over the past couple decades, the most commonly mentioned obstacle

to the production of sunflower fields under a conservation tillage

system has been the absence of appropriate EPA-approved pre- or

post-emergence broadleaf herbicides.

The postemergence grass herbicide "Poast" has been available to

sunflower producers for a number of years, as has "Prowl," one of the

preplant dinitroanilines that work on both grassy weeds and several

prominent broadleaves.

Prowl can be used in a no-till scheme since it doesn't require

mechanical incorporation. In those instances, one relies instead on

sufficient rainfall within seven to 10 days of application to

incorporate the chemical. The problem? Those areas where interest in

minimum- or no-till sunflower is highest typically are, as well,

locations where the odds of receiving a timely spring rain are mediocre

to poor.

Recent years' university research in North Dakota and Kansas has

revealed several promising pre- and post-emergence herbicides for

sunflower. But chemical company interest in labeling these products for

sunflower has been tempered by the cost of registration in comparison to

the perceived size of the market.

Finally, however, a herbicide option for sunflower under

conservation tillage emerged in 1999. Through efforts of the National

Sunflower Association and state university personnel, FMC Corporation's

Spartan® gained Section 18 registration for use on sunflower in eight

states: Minnesota, North Dakota, South Dakota, Colorado, Kansas,

Nebraska, Wyoming and Montana.

The need for a Section 18 sunflower label for Spartan was based "on

widespread kochia infestations and the lack of adequate products for

weed control in conservation tillage programs," FMC noted at the time.

Though most interest in Spartan has been as a pre-emergence application,

it also is labeled as a preplant incorporated treat-ment on sunflower.

Spartan does require precipitation for activation.

At a cost of nearly $15 an acre at the medium 4.25-ounce label

rate, the price of Spartan (which was originally developed to control

weeds in tobacco) deterred a number of sunflower growers from using it

last year. FMC has since announced a significant price reduction for

the 2000 season, however.

Steve Scott is one of numerous producers around the eight-state

region who did use Spartan on their sunflower crop in 1999.

Scott, who farms south of Burlington, Colo., planned to put

sunflower on a 300-acre field that had been in dryland corn the prior

season. "But no-till 'flowers hadn't been working for us because of the

[lack of labeled pre- or post-] herbicides," he indicates. So at the

last moment, Scott decided to work down the standing corn stalks in

order to apply and mechanically incorporate Prowl. Ironically, however,

rains delayed the tillage operation - and before the field had a chance

to dry out, he heard that Spartan had just received a Section 18 in


Scott immediately changed his plans, opting to keep the field in

no-till and use Spartan. First, though, he put on a preplant

application of two pints of Gramoxone Extra "with lots of surfactant" to

kill emerged weeds - particularly kochia, some of which were six to

eight inches tall by this late May date. The sunflower was planted the

following day.

The Spartan went on several days later at the 4.25-ounce rate,

along with 23 gallons of 32-percent nitrogen carrier solution (Scott's

basic source of applied N).

Though some High Plains sunflower producers reported crop injury

from Spartan, Scott saw none on his acreage. He says the herbicide

provided very good broadleaf control; not surprisingly, though, it was

only fair at best on the grass populations.

What have been the experiences of university weed researchers in

their investigations with Spartan on sunflower?

North Dakota State University extension weed specialist Richard

Zollinger says his trials have reflected excellent control of

broadleaves (e.g., kochia, pigweed, lambsquarter, Russian thistle).

Zollinger also reports suppression of mustard, cocklebur, ragweed and

the foxtails. The effective residual control period, he notes, has

been six to eight weeks.

Phil Stahlman, weed scientist at Kansas State University's research

station at Hays, participated in a four-state, seven-location High

Plains Spartan project in 1999. All were no-till sites, with the

sunflower planted into wheat stubble. Stahlman reports excellent

(virtually 100-percent) control of kochia, Russian thistle and redroot

pigweed. Similarly to grower experiences in the region, the multi-state

study results reflected the need to add a product like Prowl to achieve

satis-factory control of foxtail, stinkgrass and other problem grasses.

Most incidences of sunflower crop injury from Spartan appear to be

associated with either soil texture, soil organic matter content, soil

pH and/or the timing of application, according to the university weed


Though Zollinger documented very good sunflower crop safety with

Spartan, NDSU's weed control recommendations do caution growers that

"temporary sunflower injury may occur in coarse, low organic matter

soils with pH greater than 8.0."

In the seven-site High Plains tests, two sites displayed

significant crop injury as of 30 days after application. By 60 days,

however, the sunflower plants had largely recovered and there was no

impact on final yields. Stand reduction was observed only when Spartan

was applied at higher-than-recommended rates.

As in North Dakota, High Plains weed scientists say the risk of

crop injury with Spartan is greater on high-pH (over 8.0) and

low-organic soils. Other Kansas State University research has indicated

that sunflower on soils with high levels of calcium (over 5,000 ppm)

also tends to be at more risk of injury from Spartan. Typical injury

symptoms included chlorosis, a "rippling" effect on some leaves, and

stunting. However, none of those effects translated into lower crop

yields as of harvest in the university trials.

It appears all eight sunflower states will have another Section 18

label for Spartan on sunflower again in 2000. A Section 3 full federal

label is being sought, and it is hoped it will be available for the 2001

crop season. - Don Lilleboe

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