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Head Rot Fungicides

Tuesday, August 30, 2011
filed under: Disease

The single most devastating disease in sunflower is Sclerotinia head rot. It is an ugly disease that can be seen from the road at 65 miles per hour. It hits the crop when it is close to maturity, just weeks after the sunflower showed all the promises of a potentially great crop.

It’s sort of like being teased by the prettiest girl on the playground all day, only to have her drop you on your head when the bell rings.

Researchers have always looked at a three-pronged approach in dealing with this disease: crop rotation, genetic resistance and fungicides.

Fungicides for head rot have not been available once the crop is up and growing — but now it appears that several new fungicides may be labeled as soon as for the 2012 growing season.

For the past 10 years, researchers have been testing a host of labeled and experimental fungicides in misted trials in the Dakotas, Minnesota and Canada. The misted trials duplicate the disease requirements of continuous wet conditions through the bloom period. Pathogen spores are sprayed on the face of the head to ensure infection will occur each year.

Under these worst-case scenarios, several fungicides have reduced the severity of the disease when compared to the untreated checks. In some locations, the disease simply overwhelmed the entire plot and no differences were apparent.

Two products showing promise are

Endura® (Boscalid) and Vertisan™ (Penthiopyrad), both of which could have 2012 labels.

Sunflower is on the Endura master label, so all of the residue work has been completed. This is allowing BASF to conduct large field-scale testing now in 2011 without having to destroy the treated crop. Testing is planned for this season in eight to 12 fields of either confection or oil-type sunflower. Fields in the more northerly region will be selected where the crop may be vulnerable to natural head rot infestations, according to Kent McKay, BASF technical service rep, located in north central North Dakota. “We will be spraying a portion of a field, 20 to 40 acres, by air to determine if we can manage the disease in a commercial environment,” McKay explained earlier this summer. “We will be depending on natural disease infection.”

Specialists from BASF and universities will be looking at rates, application timing and multiple applications. Confection processing companies will be providing quality assessments. McKay reported at the June 2011 NSA Summer Seminar that Endura should provide 14 days of protection. That should take the plant through the bloom stage. Later infections can occur after bloom, so a second application may be needed depending on weather conditions.

McKay anticipated that the first application would occur at early bloom when about 10% of the ray petals are showing. “We can tank mix Endura with insecticides, so it will be a one pass application,” he said.

He expected that a second application would be made in some of the test fields at petal drop. The key is that Endura protects the plant and must be applied before infection takes place. It won’t help as a rescue treatment.

If all goes well this year, BASF officials will market the product to sunflower growers in 2012 as a head rot suppressant. “We need to learn a lot of things this fall before we go full steam ahead next year. Head rot is a real challenge to manage, and we have a good product — but not a silver bullet,” McKay stated.

The second product, Vertisan, is from DuPont. Vertisan, like Endura, is a Group 7 fungicide. It is also a preventative and has translaminar or systemic properties. The product has been part of misting fungicide trials in the U.S. and Canada.

Doug Meadows, who is working on the Vertisan launch project, reports that Vertisan may be on the market for 2012, subject to EPA and state approvals. Because the product is not yet registered, no sizeable field tests can be conducted this year. But the product will be in a variety of nursery trials.

Scientists at DuPont understand that Sclerotinia head rot is a huge challenge for a fungicide. “We expect Vertisan will be a useful future tool for helping sunflower producers manage Sclerotinia,” Meadows states. But he cautions that small-plot trials are different than field situations when applications are made by air, with all of the environmental issues of coverage, timing, temperature, wind and humidity.

Additionally, North Dakota State University plant pathologist Sam Markell is coordinating three locations for fungicide testing to suppress head rot infections. The extensive project is partially funded through the National Sclerotinia Initiative and the NSA’s confection processors committee. There are two test locations in North Dakota and one in Scottsbluff, Neb.

In addition, the National Sunflower Association of Canada is funding a similar study at the Morden (Manitoba) Research Station. All locations are under a mist irrigation system, with Sclerotinia ascospores applied directly to the face of the sunflower. This system ensures that infection will occur so researchers will be able to get data on fungicide differences.

Markell is cautiously optimistic that we might be turning the corner on this devastating disease. Fungicides have not been available before, so this is a brand new potential tool. A great deal of learning will occur this season in the field and in small plot testing. That learning process will continue next year in the field for both Endura and Vertisan. “We will need to find a comfort level with rates, timing and application to get the most out of these new products. Head rot is such a tricky disease, and we are going to have to be patient with our expectations,” said Markell.

In the meantime, a great deal of effort continues on genetic resistance on multiple research fronts. Most of this work is funded the National Sclerotinia Initiative and is mostly conducted at the USDA-ARS location in Fargo, with partners throughout much of the U.S.

Steve Kent, NSA Research Committee chair and president of Seeds 2000, says that we have to understand that there is not one “quick fix” for this disease. “Everyone involved has recognized from the beginning that genetics combined with fungicides is the best strategy. We are all hopeful that we now have the fungicides,“ Kent said. “We know the genetics have been improving, and we expect more gains in that arena each year as we go forward.”

Detailed reports from this season’s fungicide research will be presented at the annual NSA Research Forum in January 2012.

BASF’s McKay recognizes that the field trials scheduled for Endura may not show any differences this year if the disease does not show up naturally. But getting the product in a field setting with aerial application is a critical part of commercial introduction. “I don’t wish for lots of disease in farmers’ fields. I just want a little so that we can show differences between the treated and untreated,” he observed.

— Larry Kleingartner

Editor’s Note: For a related article, “Fungicides to Control Sclerotinia Head Rot,” in The Sunflower’s January issue go to
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