Members of the Southern Soybean Disease Workers Group conduct 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 this survey for the 2011-2014 period in the midsouthern US.
|Table 1. Soybean yield loss (in millions of bushels) to diseases and nematodes, Midsouthern US states*, 2011-2014.|
|Charcoal rot (CR)||12.06||11.67||7.26||5.25|
|Soybean cyst nematode (SCN)||8.51||5.89||17.12||14.88|
|Root knot nematode (RKN)||3.36||4.73||5.39||10.82|
|Frogeye leaf spot (FLS)||1.96||2.53||10.07||12.06|
|Sudden death syndrome (SDS)||0.29||0.06||5.65||15.87|
|Reniform nematode (RN)||---||---||---||4.65|
|Cercospora leaf blight||---||---||---||3.57|
|Rhizoctonia aerial blight||1.13||0.72||0.30||2.41|
|Pod and stem blight||0.13||0.30||2.61||1.54|
|Phytophthora root rot||3.05||0.80||2.37||0.76|
|*Arkansas, Louisiana, Mississippi, Missouri, and Tennessee. From summaries provided by Dr. S. R. Koenning, North Carolina State Univ., and Dr. Tom Allen et al, Miss. State Univ.–DREC.Majority of losses to major diseases were:
a2011: CR–all states; SCN–Ark., Mo.; RKN–Ark.; PRR–Mo.; FLS–Tenn.
b2012: CR–negligible in La.; SCN–Ark., Mo., Tenn.; RKN–Ark.; FLS–Miss., Tenn.
c2013: SCN–Miss., Mo., Tenn.; FLS–all states; CR–none in Mo.; SDS–Mo., Tenn.; RKN–negligible in Tenn.;
d2014: SDS–negligible in La., Miss.; SCN–none in La.; FLS–all states; RKN–none in Tenn.; CR–none in Mo.; RN–La., Miss.
|Table 2. Estimated yield lost to diseases in indicated Midsouth states in the 2011-2014 period. Data in last row are total value of lost yield each year in millions of dollars (lost yield x $10/bu) for the five Midsouth states (using production data by state from NASS).|
|%||Bu. x 1 Mil.||%||Bu. x 1 Mil.||%||Bu. x 1 Mil.||%||Bu. x 1 Mil.|
A summary of the above estimates of soybean yield lost to diseases and nematodes in the above five midsouthern states follows.
- In the 2011-2014 growing seasons, the most damaging pests were charcoal rot (CR), soybean cyst nematode (SCN), root knot nematode (RKN), and frogeye leaf spot (FLS). These pests were significant in all states in most years.
- Sudden death syndrome became a significant pest in 2013, and was a major yield-reducing pest in all states except Louisiana and Mississippi in 2014.
- Reniform nematode and cercospora leaf blight became significant damaging pests in 2014 for the first time during the recording period.
- Bacterial diseases were not a significant factor in any state during the period.
- Viruses contributed to significant yield loss only in 2013, and they were a factor only in Arkansas and Mississippi in that year.
- Losses to FLS increased signficantly in all states in 2013 and 2014. This may be associated with the increasing resistance of the FLS pathogen to fungicide control.
- The increasing losses to RKN that occurred in all states except Tenn. emphasize the need to develop resistant varieties to combat this pest.
- In 2013 and 2014, the latest years of the survey, soybean yield losses to disease pathogens and nematodes approached or exceeded 10%.
- The relatively low loss to stem canker in all 4 years 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 fungicide for control of 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 above estimates and summary points result in the following important tenets for disease management in the Midsouth soybean crop.
- Diseases and nematodes pose a constant threat to soybean production in the midsouthern US. Economic losses calculated using a commodity price of $10/bu approached $1 billion in 2014.
- Resistance management must be constantly practiced in order to protect the efficacy of current fungicides that are used against disease pathogens, as indicated by the increasing prominence of FLS that is known to be increasingly resistant to the strobilurin fungicides.
- 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 that negatively affect soybeans.
Composed by Larry G. Heatherly, Mar. 2015, email@example.com