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Fungicide & Plant Health

Wednesday, April 1, 2009
filed under: Optimizing Plant Development/Yields

Presidential politics and economic challenges weren’t the only issues generating headlines in sunflower country during 2008. So too was that four-letter disease called rust — and the headlines it spawned resulted in considerably more use of a fungicide with a similar name.

Vince Ulstad, technical services representative for BASF Ag Products, says the use of Headline® on sunflower in 2008 was nearly triple that of the previous year. Much of the increase can be attributed to rust management; but not all. Headline is promoted by BASF as a Plant Health™ product for sunflower; and for some growers, that was the primary reason for applying the fungicide.

The “Plant Health” designation basically means this broadspectrum fungicide not only protects plants against specific diseases; it also helps plants ward off various environmental stresses — frost, drought, hail, etc. — that may impact them during the course of the growing season. Doing so allows the plants to then grow more efficiently, ultimately producing higher yields.

“We had a strong feeling, going into the last week of June and the first part of July, that there would be a significant increase in the acreage treated with Headline — simply because of the value of the crop and the desire to maximize production,” Ulstad recounts. “Certainly, the presence of rust forced a lot of growers to spray who maybe wouldn’t have otherwise; but I think we were looking at easily doubling the amount of acres sprayed — even in the absence of a rust epidemic.”

Anecdotal reports suggest a broad range of results from Headline applications in the absence of rust during 2008. A South Dakota grower, for instance, split four quarter-sections, applying Headline on half of each field and leaving the other half untreated. He reported an average yield benefit of 600 lbs/ac — and this in an area where rust was not a serious issue.

Mycogen Seeds agronomist Bruce Due says one of his south central North Dakota growers sprayed two-thirds of an oil-type sunflower field with Headline and left the other third untreated. “He said when he went through with the combine, he couldn’t tell any difference,” Due relates. “But I’ve visited with others who said they saw quite a difference — as much as 300 to 400 pounds [per acre].

“It does appear that people who sprayed for rust kept some other diseases out [because of the fungicide treatment],” Due adds. “I really think there’s a benefit that can be achieved — maybe not every year; but in a year like 2008 where it was very wet later in the season, those sunflower stands that were sprayed held off diseases better than their counterparts that weren’t sprayed.”

Jason Hanson has a similar perspective. The Winfield Solutions (affiliated with Croplan Genetics) regional agronomist believes the Headline plant health feature “is pretty viable with sunflower — even in the absence of rust.” In the North Dakota cases with which he’s familiar, “there was almost always a positive response to Headline.” One reason why, he suggests, is Headline’s contribution to warding off other diseases like Phoma and Phomopsis — which naturally helps stalk quality.

Along with BASF’s Headline, Bayer CropScience’s Folicur® and its generic equivalent (Tebuzole®) also were used extensively for controlling rust in sunflower last year. Syngenta’s Quadris® is another labeled product. While Headline and Quadris are of the strobilurin class of fungicides, Folicur and Tebuzole are tebuconazoles. The strobilurins tend to be more effective as preventative treatments, while tebuconazoles are better at halting damage after a rust infection has set in.

That observation was borne out by Sam Markell’s findings in 2008. The North Dakota State University extension plant pathologist conducted trials at Casselton and Carrington, N.D., to compare these three fungicides’ efficacy in controlling rust. Testing in rust-inoculated plots, Markell found that Tebuzol provided superior control when applied following the initial observations of rust. When applied as a preventative treatment before the rust pustules showed up, however, Headline gave as good or better control of the disease.

Jason Hanson and Bruce Due concur with that. If rust is already well established, they believe the tebuconazoles (Folicur or Tebuzol) are more effective at halting further disease development. “But for overall plant health and a ‘catch-all’-type disease product, I think Headline serves a better use,” Due remarks. If you’re going to spray on Headline after rust is already progressing, use the 9.0 oz rate, suggests Hanson.

Markell affirms that in his trials last year at Casselton and Carrington (discussed in the December 2008 issue of The Sunflower), he found Tebuzol to give “the best control when applied right after we started seeing pustules. But nine ounces of Headline, if put on before the pustules actually formed, gave — as a preventative — as good or better control.

“So if you’re pretty sure rust is coming, if you get Headline on at the right time, you probably will fare better,” Markell observes. “But if you already have rust in your field, Tebuzol/Folicur is going to give you a little better control.”

Tank mixing the rust fungicide with an insecticide was fairly common last year in an effort to reduce application costs. Insects like the red seed weevil and banded sunflower moth are typically sprayed for at around the R5 to R5.5 stage (flowering/ early bloom). That’s not the best timing for the rust fungicides (particularly Headline), though, as the disease may already have established itself. BASF’s Ulstad says the best plant health response from Headline through the years has come when it’s applied during sunflower’s R2 (mid-bud) to R4 (ray petals first visible) growth stages.

“There were many situations where [the tank mix] worked out fine last year — if they weren’t in an area that had rampant rust,” Ulstad remarks. “But for those guys who waited just to be able to [tank mix Headline] with the insecticide — or who opted not to put on the insecticide a little earlier for that optimum Headline timing — I think there were some fields where the rust got away from them.”

One alternative, Ulstad suggests, would be to apply a lower rate (e.g., 3.0 oz) of Headline during the plants’ vegetative stage. “The most logical time would be when the grower is putting on his post herbicide so you could tank mix it.” That would provide “some coverage on the lower part of the canopy where the rust infection tends to start.”

The idea, Ulstad says, is to “protect those lower leaves, knock out some of the inoculum so you don’t have as much pressure to begin with — and slow up the development of the disease.” Were the rust to progress, that early treatment “may buy us more time, so we don’t have to come back with a follow-up application until in that R5 or beyond stage.”

Perhaps the biggest lesson of 2008 was the critical importance of application timing for the fungicide. “The key word, in terms of both scouting and treatment, is ‘sooner,’ ” says Winfield Solutions’ Jason Hanson. Waiting until the R5 stage just to eliminate an application pass is very tempting, he admits; but the result could well show up as increased yield loss that more than offsets any savings in treatment cost.

Instead, Hanson likes the idea of tank mixing a low rate of Headline with the herbicide “when you are going over the top to kill wild oats and foxtail.”

— Don Lilleboe
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