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Can Fungicide Benefit Yield Even w/Disease Absence

Wednesday, April 2, 2008
filed under: Optimizing Plant Development/Yields

Gary Wagner kept glancing at his yield monitor while harvesting the Polk County, Minn., confection sunflower field last fall. What he saw was, in his words, “almost too good to believe.”

Half of the 80-acre field, owned by Wagner and brothers Wayne and Daryl of AWG Farms, had been sprayed with Headline® fungicide. The other 40 acres (in alternating 20-acre strips) had not been sprayed. When harvest was finished, the Headline-treated strips averaged 544 lbs/ac more than the untreated strips.

The Wagners treated about 450 acres of confection and oil-type sunflower with Headline last summer. That 80-acre field provided the biggest return; but the “poorest” one still showed a 302-lb yield benefit on the treated acreage.

The Wagner brothers were not the only sunflower growers experiencing a significant yield increase due to Headline. Vince Ulstad, technical services representative for BASF Ag Products, says he’s received reports from 16 sunflower growers in Minnesota and the Dakotas who applied Headline in 2007 and compared those acres to check strips. The average yield advantage across both confections and oils ran about 240 lbs/ac. For the three-year period of 2005-07, the average benefit on grower-reported fields was 205 lbs.

There hasn’t been much university research conducted to date on the effect of Headline on sunflower in the absence of disease. A 2006 University of Minnesota on-farm trial did not show a significant difference in yield; nor did a 2005 trial at the North Dakota State University Research Extension Center near Carrington. But grower experiences and BASF strip trials have provided enough data to strongly suggest “there is something going on.”

BASF refers to Headline as a Plant Health™ product in sunflower. What does that imply — as opposed to it being called simply a fungicide?

It means, Ulstad says, that Headline not only protects against disease; it also “helps the plant mediate some of the environmental stresses (e.g., frost, hail, drought) that can come upon it during the course of a season and help that plant grow more efficiently.” The key is for the plant to be “primed” prior to the onset of such stress — akin to a human taking a protective flu shot.

What’s going on, physiologically? The same mode of action that Headline employs to kill a fungus also works on green plant cells, Ulstad explains. The big difference is that whereas green plant cells get their energy from sunlight-induced chlorophyll, a fungus does not. Instead, a fungus derives all of its energy through respiration.

“Green plant cells undergo respiration as well, in the absence of sunlight,” Ulstad observes. “So during nighttime hours, green cells respire. In that process of respiration, energy is produced, carbon is released, and there is a redirection of energy flow within the cell.”

Headline suppresses the amount of nighttime respiration going on within the green plant cells. That energy then tends to get funneled into other physiological and biochemical pathways in the plant, Ulstad notes. The eventual outcome is an overall healthier plant.

More specifically, Headline’s suppression of respiration increases the concentration of an enzyme called nitrate reductase, which is the enzyme responsible for helping the plant convert nitrate-nitrogen — the form the roots take up from the soil — into the amino form, which is the one laid down in amino acid and proteins. The result is a smoother transition in the plant’s nitrogen conversion process.

Suppressing respiration also means “there is less carbon taken in during photosynthesis that is, in turn, returned to the atmosphere during nighttime hours,” Ulstad explains. “So you effectively have a net increase in carbon retained in the plant — and carbon is the backbone of most building molecules.”

The Wagner brothers also have sprayed Headline on soybeans, in the absence of disease, in two different years. However, “I’ve never been able to pick up enough difference on the yield monitor to say there was an actual difference” between treated and untreated strips, Gary relates.

Ulstad isn’t surprised. A legume like soybeans does not experience the “bottleneck” in nitrogen conversion nearly as much as a crop like sunflower, he notes. So the improvement in conversion efficiency would be more pronounced in sunflower.

Also, “sunflower seems to be a crop that tends to attract its fair share of diseases,” he points out, “and Headline is a very broadspectrum fungicide. So that, too, increases the likelihood of response by sunflower.” Among the diseases controlled by Headline in sunflower are downy mildew, rust, Alternaria leafspot, powdery mildew and Septoria leafspot.

While Headline is labeled for up to two applications per season on sunflower, most growers seeking the plant health effect have applied it just once. The current recommended rate is 6.0 fl oz per acre with an adjuvant (NIS @ 0.125-0.25% v/v).

What’s the proper timing of treatment? “In the absence of any visual disease in a field, probably the best time to trigger that application preventively and proactively is to come in when the green plant starts to shift from a vegetative to a reproductive growth stage,” Ulstad advises. “In sunflower, we’re talking the R2-R4 stage (late bud to early bloom).” Application timing is a facet that needs more research, however, and Ulstad is working with NDSU plant pathologist Sam Markell to set up a protocol for treatment timing studies this year.

Headline can be tank mixed with all labeled sunflower insecticides. “So we believe the timing for insecticide treatment of some of the key insects is going to be very compatible with that for Headline,” Ulstad notes.

Since Headline-treated sunflower plants tend to stay green longer than nontreated ones, does that mean seed moisture levels also will take longer to get down to a preferred harvest level? That’s another area for study. In the Wagners’ experience, however, it was indeed the case. “The [seed] moisture was about 3.5% higher” in the treated versus nontreated sunflower, Gary indicates. “We’ll have to take that into consideration if we spray on a lot of Headline: plan for a little longer drydown period.”

It’s apparent more needs to be learned about Headline — and similar mode-of-action fungicides — on sunflower. But the initial data are promising, especially at this year’s contract prices for oils and confections. An additional 100 lbs of yield can easily pay for the investment. Some contracting companies indicate they are informing their contract growers of the Headline option, but not necessarily making a treatment recommendation one way or the other. — Don Lilleboe
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