Soybean Yield Losses to Diseases in the Midsouthern US, 2017
Members of the Southern Soybean Disease Workers Group participate in an annual survey to estimate yield losses to soybean diseases in the southern US. These estimates are solicited from research and extension pathologists throughout the region, and are based on field surveys, plant disease samples, variety trials, questionnaires to Extension Specialists, research plots, grower demonstrations, private crop consultant reports, foliar fungicide trials, and sentinel plot data. Production losses are based on estimates of yield in the absence of diseases.
Below are summary results from the 2017 crop year survey conducted in the midsouthern US states.
• Diseases and nematodes caused estimated soybean yield losses of 7.85%, 12.8%, 8.96%, 8.5%, and 9.1% in Arkansas, Louisiana, Mississippi, Missouri, and Tennessee, respectively.
• An estimated 71.64 million bushels of lost soybean yield was attributed to diseases and nematodes in the collective states, with a value of $716.44 billion using a $10/bu commodity price.
• In the 2017 growing season, the most damaging pests across the five states (in descending order of caused yield loss) were soybean cyst nematode (SCN), root knot nematode (RKN), frogeye leaf spot (FLS), and cercospora leaf blight (CLB).
• In Arkansas, diseases/pathogens causing the most yield loss were RKN, CLB, and SCN.
• In Louisiana, diseases/pathogens causing the most yield loss were FLS, CLB, Rhizoctonia aerial blight (RAB), RKN, and reniform nematode (RN).
• In Mississippi, diseases/pathogens causing the most yield loss were CLB, charcoal rot (CR), FLS, and RN.
• In Missouri, diseases/pathogens causing the most yield loss were SCN, sudden death syndrome (SDS), seedling diseases, and FLS.
• In Tennessee, diseases/pathogens causing the most yield loss were FLS, SCN, CR, seedling diseases, and stem canker (SC).
• CR caused significant yield loss only in Mississippi and Tennessee.
• CLB caused significant yield loss only in Arkansas, Louisiana, and Mississippi.
• FLS caused significant yield loss in all states.
• RKN caused the most yield loss (4%) in Arkansas, and was also a significant contributor to yield loss in Louisiana and Mississippi.
• SCN was a most significant contributor to yield loss in Missouri and Tennessee.
• RAB was a significant contributor to yield loss only in Louisiana.
• SC had a significant presence only in Tennessee.
• SDS had a significant presence only in Missouri.
• Yield losses attributable to viruses and bacterial diseases were near or at 0 in all five states.
The above estimates and summary points result in the following important tenets for disease management in the Midsouth soybean crop.
• The high losses to RKN that occurred in Arkansas, Louisiana, and Mississippi emphasize the need to develop resistant varieties to combat this pest.
• The low yield loss to stem canker is testimony to the effectiveness of varietal resistance as a control measure to avoid yield loss to a fungal pathogen. The virility of this pathogen is documented by the devastating effect it had in the late 1980's when planted varieties had no resistance. Since there is no efficacious fungicide for the stem canker pathogen, this is even stronger testimony that plant resistance to a fungal pathogen can be a most effective long-term tool to minimize loss to disease.
• The negligible effect of seedling diseases on estimated yield loss in most states is testimony to the effectiveness of fungicide seed treatments against seed rot and seedling disease pathogens.
• Resistance management must be constantly practiced in order to protect the efficacy of current fungicides that are used against major foliar disease pathogens such as Frogeye Leaf Spot.
• A constant effort must be exerted to provide genetic resistance to major soybean disease pathogens and nematodes in order to provide the most effective long-term defense against these pests. The effectiveness of this strategy is evidenced by the continued low effect of stem canker on soybean yield in the region.
• The major effect of SCN on soybean yield reduction in Missouri and Tennessee underlines the continued importance of using resistant varieties and crop rotation to manage this pest. It is also important to rotate varieties that have different resistance sources since SCN will adapt to varieties that have the same source of genetic resistance. Click here for details.
Composed by Larry G. Heatherly, Mar. 2018, larryheatherly@bellsouth.net