Dual-Dose Fungicide Use Grows

Fungicides have become a common preventative tool for corn growers over the past six to eight years. Once promoted primarily for commercial seed production and sweet corn, the practice has found a larger niche in attempts to increase commodity corn yields.

Most high-yield growers apply fungicides at tassel-to-blister (VT to R2) corn-growth stage. The practice has been shown to be particularly effective in years of high disease pressure. In recent years, companies have begun to promote not just one, but two sequential fungicide sprays -- with the first application coming earlier in the season. In-furrow fungicide applications are also becoming more popular -- often applied with starter fertilizer in the spring.

While some of the data looks promising with multiple-dose tactics, it's no surprise that the payoff is more likely when commodity prices are higher.

Product Lines

There are currently a number of fungicides marketed and labeled for use on corn, including some generic products.

While labels may include broader application times, BASF typically markets Headline (pyraclostrobin) for use in-furrow; Priaxor (pyraclostrobin + fluxapyroxad) for application in the vegetative stage and Headline AMP (pyraclostrobin + metconazole)for the traditional tassel to blister stage.

Bayer CropScience markets Stratego Yield (prothioconazole + trifloxystrobin) for both vegetative and reproductive stages and Proline (prothioconazole).

Syngenta markets Quilt Xcel (azoxystrobin + propiconazole) for both vegetative and reproductive stages and Quadris Flowable (azoxystrobin) for in-furrow. Many of the current recommended foliar products contain two sites of action to improve efficacy and reduce the risk of developing resistance.

Additional commercial products registered for corn include Domark (tetraconazole) marketed by Valent and Evito (fluoxastrobin) marketed by Arysta LifeSciences.

Getting the Timing Right

Caren Schmidt, BASF Fungicide Technical Marketing Manager told DTN that an application at tassel or flowering is still the best time to make a single fungicide application in corn. "If you are going to make only one application, do it at VT-R2 when the plant and its foliage needs the most protection," said Schmidt.

Randy Meyer, Fungicide Product Manager with Bayer CropScience and Eric Tedford, fungicide technical product lead with Syngenta, also weighed in favor of the VT-R2 timing for a single fungicide application.

University extension specialists generally take a conservative view of fungicide use. "In corn, fungicide response is strongly linked directly to disease pressure and historically, applications at VT to R1 give the greatest response," said Carl Bradley, University of Illinois plant pathologist. Bradley advocates using disease risk as a factor in the decision to apply fungicide.

He's also been evaluating fungicides on corn since they came into routine use and has made some keen observations. "We tested foliar fungicides on corn, over multiple years and 33 environments based on disease risk and saw an average 5.8-bushel-per-acre yield gain across all environments and locations," Bradley told DTN.

When disease pressure was low and present in less than 10 percent of the leaf area, there was an average 3-bushel-per-acre increase. In those cases, 45% of the sites achieved breakeven. However, when more than 10 percent of the leaf area was infected, there was an average 10-bushel-per-acre increase and 92% of the sites experienced financial breakeven. "On occasion, we saw yield increases in fields with low disease pressure that were profitable, but this was inconsistent and unpredictable," Bradley said.

There is ample data showing the benefits of applying fungicide on corn grown under high-risk conditions. These include: corn after corn, high residue no-till fields, vulnerable varieties, weather patterns conducive to disease outbreak or high yielding fields.

Besides making applications of fungicides at VT or R1, there is more evidence coming forth on applying fungicide during the vegetative stage and even in-furrow with the seed.

Is Earlier Better?

Over the last few years there has been a move to applying fungicides during vegetative stages and two distinct windows have appeared: V4 to V7 and V8 to VT. The V4-V7 window can include a herbicide and surfactant while the V8-VT application cannot have a surfactant. Either window could include foliar nutrients.

A number of years ago, it was observed that early fungicide applications made with a surfactant at or after V8 would cause blunt ear formation. Taking out the surfactant eliminates this risk.

Schmidt explained that BASF has been testing early applications on corn, prior to tassel and have seen an incremental yield benefit to adopting an early application. "There are early-season diseases that cause the earlier leaves to die sooner. A fungicide not only helps control those diseases, but it physiologically stimulates these leaves so they stay active on the plant longer before dying naturally."

Randy Myers, Bayer CropScience fungicide product manager, said his company has also evaluated sequential early and late applications. "Our data show two sprays are most consistent in yield response and it’s easy to work the first treatment into the operation along with a herbicide spray. An early spray helps protect the middle canopy by reducing infection pressure, and controls early infections of gray leaf spot, anthracnose and northern corn leaf blight and diseases that overwinter in the residue. If we keep the bottom leaves cleaner longer, this delays the infection of leaves higher on the plant. And while protecting the lower leaves, the fungicide helps preserve the integrity of the lower stalk where carbohydrates and nutrients are stored," Myers said.

Tedford agrees that the traditional window is VT to R1 is the most opportune, but he considers the early application at V4 to V8 is another good option. "When it is dry, or with an early sustained drought such as 2012, we saw a very good (yield) response to an early fungicide application. Leaves were more turgid and extended and there were physiological benefits with improved water-use efficiency and sustained photosynthesis."

However, Bradley, who has been investigating fungicide applications during vegetative stages on corn, believes that more research is needed to gain a better understanding of the effect of these vegetative-staged applications. "We have not seen a consistent response with early applications and it’s hard to contribute a response to disease early. Anthracnose leaf blight of corn is a disease that appears early, but corn tends to outgrow this disease when temperatures warm up and corn begins to grow rapidly." He continues his investigations.

Each year Iowa State University evaluates foliar fungicides for disease management and yield response. Those results have just been released for the 2012 crop. Keep in mind the dry year did not result in a lot of disease.

In general, fungicides resulted in more of a positive effect on yield at the northern locations than the southern Iowa locations. The mean yield response of an application of fungicide at V5 (4.9 bpa) was lower than that of an application during the reproductive growth stages (5.5 and 6.2 bu/A for R1 and R2 applications, respectively). A double application of fungicide at V5 and R1 resulted in a similar yield response across all locations to one application at growth stage R2 (both 6.2 bpa).

Six fungicides were tested and you can read the results here: http://www.extension.iastate.edu/…

Application In-Furrow

One of the possible new approaches is adding a foliar fungicide in-furrow either alone or with starter fertilizer. BASF is testing the use of fungicides in-furrow on corn and Headline is labeled for this use in corn. Schmidt explained that there are benefits from an in-furrow application, such as suppression of soil borne Rhizoctonia. "We see greater vigor and more uniform and rapid emergence. And under cold soil conditions, we see increased seeding growth and root development and emergence a day sooner." She added that growers can use either Headline in-furrow or Stamina (pyraclostrobin) seed treatment.

Tedford said Syngenta have been testing Quadris in-furrow for a few years. Quadris is labeled for this use, but he says while they recognize the benefit, the results have not been as consistent as those from V and R stage applications.

(PS\SK)

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