Eliminating the “Black Stuff”
With one painful bite into the “hard piece of black stuff” that can inadvertently find its way into a bag of in-shell sunflower seeds, a confection sunflower processor might lose a customer, or worse, have a liability situation on its hands.
The black stuff is sclerotia, the byproduct of the fungal disease Sclerotinia (also called white mold) that can affect the quality and yields of sunflower, canola, soybeans, dry edible beans, peas, lentils, and other broadleaf crops.
To help address the disease problem, Congress has funded a Sclerotinia Research Initiative of about $1 million each of the past two years in a multi-state, multi-institutional, multi-crop effort.
Crop scientists from about 10 states and Canada met earlier this year in the Twin Cities to report progress and results from a second year of research funded by the Initiative. Close to two dozen papers were presented in three distinct research areas including epidemiology (how Sclerotinia develops and spreads); chemical and biological control; and germplasm enhancement/variety development.
Sclerotinia research in sunflower includes testing of new and existing fungicides to control head rot. Extensive testing of one BASF fungicide close to commercialization will be conducted this summer. The product (Boscalid, Endura 70%) has been registered by EPA but a label for sunflower is pending further evaluation data.
The Initiative is also funding the evaluation of commercial sunflower hybrids and USDA breeding lines for Sclerotinia tolerance. Misting systems are used in plots at Carrington and Fargo, N.D., and Brookings, S.D., to induce a controlled environment for evaluating head rot in hybrids. Testing indicates that a number of confection and oil hybrids are making progress toward improved Sclerotinia tolerance.
USDA is utilizing a system to test hybrids for stalk rot tolerance by feeding the roots a Sclerotinia-infected mixture of seeds. The system may lead to greater reliability in rating tolerance of commercial hybrids, and will be especially important to producers who wish to grow sunflower after soybeans.
DNA markers associated with Sclerotinia tolerance in sunflower are also being developed by USDA personnel in Fargo, enabled in part by the Sclerotinia Initiative. The DNA markers help sunflower geneticists to quickly determine if Sclerotinia-resistant genes have been transferred to a crossed progeny, expediting the evaluation of sunflower breeding material.
As well, considerable work is being conducted on broad leaf crop rotations in multiple locations, with an increasing understanding of disease and crop interactions. While research advancements have been made in recent years, there is still much to be learned, even with basic research questions, such as why sunflower roots are at risk to infection, as opposed to soybeans and other broad leaf crops that are vulnerable only to foliar (airborne spore) infection.
Sclerotinia in Sunflower
Sclerotinia can affect sunflower in three ways:
1) Wilt (basal stalk rot) from infected roots caused by germinating sclerotia.
2) Mid stalk rot, caused by ascospores (airborne spores) that infect leaves and progress to the stalk. Sclerotia in the soil become saturated and extend mushroom-like fruiting bodies that omit millions of ascospores.
3) Head rot, caused also by ascospores, can cause head rot during an extended wet period in late July/August. Head rot is the most significant of the three infections because it impacts yield and quality.
Eliminating as much of the sclerotia in the soil is one step in dealing with disease management. At this point, research indicates that no-till may be better than tillage to accelerate the destruction of sclerotia. Instead of being buried beneath the soil surface, the sclerotia stay exposed at the soil surface. Weather, including the freezing-thawing cycle, results in degradation and cracks in the sclerotia, allowing other natural parasitic fungi to enter and destroy sclerotia in the soil.
There are a number of natural parasites in the soil throughout this region.
The commercial product Intercept WG is essentially a concentrated “bottled” form of a natural microbial parasite (Coniothyrium minitans). The product attacks sclerotia after it is applied in the soil.
The product’s manufacturer, Encore Technologies, advises on its web site (www.encoretechllc.com. Click on the “products” link, then “Intercept WG.”) that “for soils anticipated to be planted with sunflowers, fall application yields the most effective and economical use rates. To avoid turning up sclerotia from lower untreated soil layers, treated soils should not be spring plowed or tilled below the treated soil layer before planting sunflowers.” The web site also lists other pesticides that can and cannot be tankmixed with Intercept.
Since the product has only been in the market for a few years, growers and crop scientists are still analyzing it. Research indicates the product is not a quick fix, but does appear to hasten the destruction of sclerotia in the soil. Research also indicates that highly alkaline or pH soils seems to play a role in reducing the efficacy of Intercept.
Whether or not the product needs light incorporation is another aspect of the product that crop scientists are analyzing. Early results at the USDA-ARS Northern Great Plains Research Laboratory in Mandan, N.D., indicated that no-till plots treated with Intercept had less Sclerotinia compared to Intercept-treated plots that were tilled. Additional research and field experience now indicates that Intercept may be applied at planting with no further soil disturbance.
Detriment to Confection Quality
Sclerotinia has a direct effect on confection sunflower quality. Ron Klinge, quality systems manager with Dahlgrens & Co., Crookston, Minn., gave an overview at the Twin Cities Sclerotinia Research Meeting about how the problem can affect confection sunflower processing.
“About 90% of complaints from consumers are (off) flavor, but about one third are definitively sclerotia related,” he says.
He explains that confection sunflower processing begins by separating seed into small, medium and large sizes, with small going to the bird food market, medium processed for the kernel market, and large for the in-shell roasted seed market.
There’s a thorough cleaning process with state-of-the-art equipment that cleans and separates foreign material on the basis of difference in size, shape, texture, surface texture, density and color. “Unfortunately, sclerotia are also the same size as our sunflower seeds and kernels, with similar textures and densities which really creates a challenge in our cleaning systems,” he relates. Seed isn’t just damaged from a foreign material standpoint. Head rot can cause the seed itself to become discolored and develop an off-taste that is amplified when seeds are roasted.
Klinge says Sclerotinia affects the bottom line of both producers and processors, resulting in farm-gate discounts and additional processing costs.
“When we take out sclerotia, we are also losing good kernel. It is just inevitable that we have shrinkage involved in that. Sclerotia can cost us about 5 to 10 % loss of good kernel because of our need to remove it in the process,” he says. “This past year fortunately was good but we remember other years and have to compensate for those. There is investments in additional equipment, even if we don’t always need it, which adds cost in energy, labor, and overhead that goes in that price per pound. It’s all a byproduct of sclerotia removal.”
Klinge points out that confection processors try to use all the components of the sunflower seed, including material that may not be suitable for human consumption, but used as a nutritional supplement in the cattle feed industry. “But when sclerotia is too high, even they can’t use it, it has to go to compost.”
Sclerotinia is a difficult disease for researchers as well. Prior to the Sclerotinia Initiative’s federal funding, most public researchers and their administrators were unwilling to risk time and money in researching the disease, because of the limited potential pay back. The Initiative has changed that and progress is being made.
More information about the Sclerotinia Research Initiative, and research proceedings from the Twin Cities meeting, can be found online at www.sclerotinia.com – Tracy Sayler
For related articles, go to www.sunflowernsa.com. Click on “Sunflower Magazine,” then “View Archives” and “Disease.” NDSU has a bulletin, “Sclerotinia Head Rot of Sunflower,” online at http://www.ext.nodak.edu/extpubs/plantsci/rowcrops/pp1193w.htm
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