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Hoods for 'Flowers

Tuesday, April 1, 1997
filed under: Weeds

A bunch of hoods likely will be passing through some U.S. sunflower fields in late spring/early summer. No, we’re not talking about an influx of big-city street gangs into rural America. The hoods will be there for a very positive purpose: to help producers control between-row weed populations in their emerged sunflower with a broad-spectrum herbicide.

These “hoods” are hooded sprayers designed to apply herbicides in row middles while protecting the crop itself from the chemical. They’ve been used in crops like corn, soybeans and cotton; and now sunflower growers in at least two states apparently will also have that option.

The reason? Special Local Needs (SLN) 24-C labels have been applied for in both North and South Dakota for the use of Monsanto’s Roundup® Ultra herbicide on sunflower under a postemergence shielded spray application. As this issue of The Sunflower went to press, the North Dakota Department of Agriculture had just approved this special use label. South Dakota regulators were still considering the application as of late April.

So North (and perhaps South) Dakota sunflower producers will have the option of adding an important weapon to what currently is a very narrow postemergence herbicide arsenal. Currently, the only other post-herbicides registered on sunflower are Assert for wild mustard control and Ultima 160 for annual grasses. Use of Roundup would assist in battles with problem broadleaves like kochia, pigweed, Russian thistle and common lambsquarters, along with the grasses and volunteer grains. No-till and minimum-till producers could particularly benefit from this treatment.

(Note: As of this writing, applications had not been received in either Kansas or Colorado for permits to use Roundup under a shielded spray method. Interested growers in those and other states — as well as South Dakota — are encouraged to first check with their Monsanto representative and/or university extension weed specialist regarding the legality of this specific use for Roundup on sunflower in their state.)

Since the Dakota SLN permits were still “up in the air” as of the latter part of April, Monsanto had not yet published a supplemental label for Roundup’s use with hooded sprayers in sunflower. When it does, however, the recommendations likely would fall along the lines of those for a crop like corn. They likely would include (but may not be limited to) the following:

• The spray pattern is to be completely enclosed on the top and all four sides by a hood, thus shielding the crop itself from the spray solution.

• The hoods should be set up and operated in a manner which avoids their bouncing or being raised off the ground, as those circumstances could allow spray particles to escape and contact the crop, thereby injuring or killing it. The hoods should be situated on the ground or just skimming the soil surface.

• No more than one quart of Roundup per acre per application would be recommended, with a maximum of three quarts per acre per year for hooded sprayer applications.

• The crop should be at least one foot tall, and a minimum eight-inch untreated strip should be left over the crop row (e.g., if in 30-inch rows, the maximum width of the spray hood would be 22 inches).

• Spraying would not be recommended if wind speed exceeds 10 miles per hour. Maximum suggested tractor speed is five mph. The hooded spray units should be equipped with low-drift nozzles and, in general, have only components approved for this particular use.

• If the herbicide does come into contact with crop leaves or other plant parts and injury does occur, any damages are considered the responsibility of the applicator.

ow feasible is this method of postemergence weed control in sunflower? University weed scientists in both Kansas and North Dakota have conducted studies on sunflower with Roundup applications under hooded sprayers. Their results indicate it can be an effective method of weed control in row middles.

In 1996 tests at Hays, Kansas State University agronomist Phil Stahlman applied Roundup Ultra at 12 and 20 fluid ounces per acre, each at 25 and 30 psi spray pressure, and at three stages of sunflower development (four, 12-14 and 16-20 inches in height). Redroot pigweed, tumble pigweed and stinkgrass were the three primary weeds in the plots.

“All Roundup treatments controlled redroot pigweed, tumble pigweed and stinkgrass completely within the 18-inch bands between crop rows, regardless of herbicide rate, spray pressure or crop stage at the time of application,” Stahlman reports. There were no significant differences in sunflower yield or test weight among the three crop-stage treatments, though there was “a trend of increasing sunflower yield with each later Roundup application.” Stahlman adds that some smaller sunflower plants were injured by coming into contact with the spray hoods; also, “leaves of larger plants were higher off the ground and less likely to come in contact with any spray fines that escaped from under the spray hood.”

The 1996 Hays experiment “confirmed previous research that showed Roundup, when applied with protective hoods or shields, to be an effective between-row postemergence herbicide treatment in sunflower,” Stahlman concludes. “Though not statistically significant, it appeared that crop safety increased with crop growth stage. Sunflower [plants] less than 12 inches tall at the time of application were susceptible to mechanical injury as well as being more susceptible to the herbicide.”

Tests by North Dakota State University weed scientists last year also indicate that Roundup Ultra is effective in controlling broadleaf weeds between rows in sunflower fields. The NDSU researchers looked at two rates of Roundup (1.88 and 3.75 oz./A) applied to 10-leaf sunflower plants which were about 10 inches tall. The primary broadleaf weeds being treated were redroot pigweed, common lambs-quarters and wild mustard. A flat-fan nozzle on the hooded sprayer delivered 25.5 gallons per acre at 40 psi. Weed control was quite satisfactory, while injury to the sunflower plants was virtually nil. — Don Lilleboe
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