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Surface Applications Of Granular Herbicide

Friday, August 1, 1997
filed under: Weeds

By the time the first snow has fallen on his south central North Dakota fields, Allen Entzie is already well on his way toward controlling weeds in the next year’s sunflower crop. In fact, other than a likely spring preplant burndown treatment, he’s finished.

The Lehr, N.D., no-till producer utilizes a strategy that’s not listed on his herbicide’s label — yet is perfectly legal: a late-fall surface application of either Treflan or Sonalan granules, relying strictly on snow melt and early spring rains for incorporation of the chemical. Over the past several years, Entzie has treated an average of 500 sunflower acres annually (his own plus those he has custom applied). He says weed control results have been quite comparable to those of area conventional or reduced-till sunflower growers who have incorporated granules via mechanical means.

That’s not a big surprise to Todd Geselius, Fargo-based field development specialist for DowElanco, manufacturer of Treflan and Sonalan. He and other DowElanco personnel cannot and do not actually recommend leaving incorporation solely to Mother Nature; however, they also recognize that surface application of granules has worked for a number of producers. Because this method of incorporation is not part of the herbicide labels, however, DowElanco is under no obligation if weed control results are unsatisfactory.

Regardless of incorporation method, fall granular application is generally preferable to spring in the Northern Plains, Geselius notes. “The main reason is the moisture aspect,” he says. “You’re pretty much assured you’ll have the moisture to bring the compound off the granules [with a fall treatment] — plus, you have time for it to get off the granules and into the soil where the weeds will be affected by it.”

Entzie did a spring surface treatment one year, covering the snowless field with his 48-foot pickup-mounted Valmar Air-Flow applicator. Those results were quite satisfactory, “but you are counting on another snowfall or at least a good rain,” he points out. Another complication could be a malfunctioning foam marker due to still-cold temperatures, thereby resulting in herbicide skips.

Both Entzie and Geselius agree that the later in the fall the granules are spread, the better. “If you’re going to lay it on the surface, do it as late as you can — just because there’ll be less time for bad things to happen to it,” Geselius advises. Degradation of the chemical could be a problem if the granules are lying on the soil surface during warm autumn days. “If you have some nice stubble, I wouldn’t be afraid to spread it after about the 20th of October,” Entzie remarks. “By then the sun’s angle is low enough that you’re not getting the direct sunlight on the ground.” He has applied the granules as late as December.

Those who’ve had experience with the surface-applied granules under no-till conditions also point out that this approach generally will produce more-consistent results on fields which have been under no-till for at least three years, as compared to fields in their first or second year of direct seeding. “These materials don’t move very rapidly in the soil,” Geselius observes. “So wherever you place the chemical, it won’t go very far. If you’re just starting out in no-till, those weed seeds are spread throughout the top few inches of soil. So if the compound is spread on top, it really doesn’t have the opportunity to get down and work on the roots of those deeper-germinating weeds.”

Results of Canadian experiments in 1993 and 1994 support both the fall-applied advantage and the consistency of control in “veteran” no-till fields. Surface applications of ethalfluralin (Sonalan, which is marketed as “Edge” in Canada) granules were compared against a shallow incorporation with a rotary harrow. The fall-applied granules were superior to a spring treatment in both the degree and consistency of weed control. DowElanco also reported that in the spring-applied experiments, “weed control on land that had been in direct seeding for three years or greater was more consistent than on land [with] less than three years in direct seeding.”

Spring-applied tests conducted by Kansas State University in 1994-96 produced mixed results, depending upon the amount of spring moisture received and the weed spectrum being treated. Those experiments suggested that a surface-applied granular treatment is most feasible for fields where grasses (other than volunteer cereal grains) are the major problem; but less so where certain broadleaves, such as kochia or Russian thistle, are most troublesome. In many cases, a burndown treatment and/or postemergent herbicide may be necessary.

Several summary points seem apparent regarding the use of a granular herbicide surface application on upcoming sunflower fields:

• It does work — though probably not as consistently year in and year out as a mechanically incorporated treatment. With the limited number of herbicides available to no-till sunflower producers, however, it can be another viable option.

• Adequate moisture is essential for activation of the chemical, be it from melting snows and/or significant spring rainfall. A late-fall surface application usually makes more sense in the Northern Plains, whereas spring-applied granules could have a better fit in the High Plains.

• In addition to the surface granules, many fields likely will require a preplant burndown treatment for broadleaves and, in certain instances, some postemergence grass control. That’s especially true if volunteer wheat or barley is a problem.

• Using higher-end labeled rates is probably a good idea, since at least some chemical likely will be lost through volatilization.

• A surface application of trifluralin or ethalfluralin granules is legal as long as one does not exceed label rates. However, if the producer has unsatisfactory results for any reason, there would be no recourse against the product’s manufacturer. — Don Lilleboe
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