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Disease Trends   2002 - 2017

Friday, January 25, 2019
filed under: Disease

       The National Sunflower Association has conducted the Sunflower Crop Survey since 2002.  With the exception of 2004, the survey was carried out annually until becoming a biennial survey in 2013.  Volunteers from all levels of the sunflower industry visit sunflower fields to survey the crop.  They look for yield and production practices, weeds, insects, diseases, and bird damage. 
       The collected data are useful to all involved in the sunflower industry.  For producers, the information can help them make better management decisions. Researchers use the information to guide future research.  And the National Sunflower Association relies on the data to determine which areas of research to fund. 
       Dr. Sam Markell of the NDSU Department of Plant Pathology and other pathologists have taken the data specific to disease and further examined the trends in disease. Markell shared those findings at the 2019 NSA Research Forum. 
       Markell says comparing sunflower disease issues in North Dakota to those in Texas wouldn’t make sense, because the climate, soils and other growing conditions are so different in those areas.  So, he and his team separated the growing areas into these four geographic regions:
       •  Region 1 — North Dakota and Minnesota
       •  Region 2 — South Dakota
       •  Region 3 — Nebraska, Colorado and Kansas
       •  Region 4 — Texas

       “There is so much difference in the growing factors in those states, that we felt splitting them into regions made the most sense,”?Markell states. “In North Dakota and Minnesota, temperatures are cooler and there’s not a lot of irrigation.  Compare that to Texas where temperatures are extremely hot and 75% of the crop is irrigated.  Those things make a difference when we look at the disease trends.”
       Across all the years, survey crews looked at more than 2,200 fields in the Dakotas, Minnesota, Nebraska, Kansas, Colorado and Texas.  Markell says on the disease side, as many as 10 different diseases were identified. He focused his presentation on the top five diseases: downy mildew, rust, Sclerotinia head rot, Rhizopus head rot and Phomopsis stem canker. Here is a brief summary on his observations for each of the diseases in the various regions:

Downy Mildew

       Markell says downy mildew might be the only disease that is under-estimated on the survey.
       “Downy mildew often strikes early in the season,” he explains.  “Plants will die before the survey is done at the end of the growing season; so those plants that had downy mildew are not around when we are surveying fields.  I’d say it’s probably underrepresented by about 50%.”
       Markell says downy mildew shows up in every region, but is most prevalent in Region 1 — which, he explains, stands to reason because the disease thrives in cooler temperatures common in North Dakota and Minnesota.  Although he expected to see more of the disease in Texas because of irrigation, it has only shown up in one year of survey in the Lone Star State.   


       Markell says rust is the most common of the top five diseases in the sunflower survey. 
       “We found rust in every region we surveyed; and there are regions where we are approaching 100% of fields with rust,” he told the Research Forum crowd.  “But that doesn’t mean it is severe; it simply means it is occurring.”
       Still, rust can lead to high yield loss. The economic threshold for spraying is 1% during bloom; and when surveys (which are conducted at the end of the season) show as little as 3 to 4% rust occurrence, yield was likely lost.  Markell says some fields with 20% rust are completely wiped out. 
       According to Markell, rust spiked in the Central Plains and in North Dakota in 2009, leading to high yield loss.  That’s when the National Sunflower Association decided to fund research on rust. He says that research — and the development of the fungicide thresholds used today — would not have happened had it not been for the NSA survey.

Sclerotinia Head Rot

       Markell says Sclerotinia head rot is most common in Region 1, as the disease thrives in the cooler weather in North Dakota and Minnesota.  There isn’t much Sclerotinia south of South Dakota, he says.
       “There really isn’t a lot of Sclerotinia head rot in South Dakota, even.  I expected more in the High Plains and in Texas because of irrigation, but the heat makes the disease reasonably uncommon,” he points out. 
       Markell says the data collected on Sclerotinia through the sunflower survey across the years has proven valuable to researchers.  “We don’t have a lot of details on what level of yield loss the disease causes on a large scale,” the NDSU plant pathologist points out.  “We have data from research plots; but this survey gives us a better look at the big picture.  Demonstrating how much yield loss Sclerotinia head rot causes is critical when researchers try to leverage research funding from other sources, such as the National Sclerotinia Initiative.”

Rhizopus Head Rot 

       Markell says Rhizopus head rot is the other head rot that has researchers concerned.  The instances of this disease are flip-flopped from Sclerotinia, with most Rhizopus found in Texas and Region 3 (the Central High Plains), versus the Northern Plains. 
     “There is less of this disease the farther north you go, which again makes sense because Rhizopus likes hot temperatures.”
       Summer hail storms are another factor that leads to Rhizopus.  Markell says when hail storms break out in the hot summer weather, Rhizopus commonly follows.  In 2015, after several severe hail storms, there was a spike in Rhizopus in North Dakota, he adds.  He calls the disease “really common and really damaging in the hotter states.”

Phomopsis Stem Canker

         Markell says if there is a consistent trend among any of the diseases looked at in the sunflower survey, it is with Phomopsis stem canker. The disease is trending upward. 
         “It is increasing in every region but Texas,” he notes.  “More and more fields are being hit with Phomopsis.  You will see some fields totally wiped out by the disease, and others with none.  The level of yield loss will partially depend on how early the field is infected.”  
         So, what does all this mean?  Markell says it points to the significance of the biennial NSA sunflower survey.  
         “This survey is really unique,” he says. “I work with eight different field crops and am associated with others.  There is no other crop that does a survey like this one. This survey is really helpful, and I see tons of potential in it.  Data collected are powerful.  They give researchers an advantage when applying for federal money. They also give the board members of National Sunflower Association a great tool to help them make decisions when they fund research or leverage support for research. Most other crops simply don’t have data like these.” 
         Markell says the sky is the limit when it comes to using these data to come up with solutions to help sunflower producers — not just for diseases, but also for insects and other factors that impact yield. 
         The NSA Sunflower Survey will be conducted again in the fall of 2019. Teams of volunteers will survey numerous fields across the sunflower growing regions.  Anyone interested in becoming  involved is invited to contact the National Sunflower Association. 
— Jody Kerzman         
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