US Soybean Rust Detection and Aerobiological Modeling

November 2004 presentation.


  • Dan Borchert, Glenn Fowler and Roger Magarey (USDA-APHIS-PPQ-CPHST-PERAL)
  • Daryl Jewett (USDA-APHIS)
  • Annalisa Ariatti (UIUC)
  • Scott Isard (PSU)
  • Manuel Colunga and Stewart Gage (MSU)
  • Glenn Hartman and Monte Miles (ARS and NSRL)
  • Thomas Keever and Charlie Main (NCSU)
  • Jeff Grimm, Aaron Hunt and Joe Russo (ZedX, Inc.)


  • The Integrated Aerobiology Modeling System (IAMS) was used to simulate daily soybean rust spore movement (Isard et al., 2004)
  • Viable spore deposition (logarithmic) is modeled from September 15 to 19, 2004 in association with Hurricane Ivan
  • Uncertainty is associated with spore source strength and the absolute quantity of spores

Aerobiological Model Assumptions

  • Source area (17,000 sq Km) was from soybean production areas in northwestern South America
  • Spores were released near midday from August 30 to September 9, 2004
  • 25% of the source area was infested with soybean rust
  • 6 million spores were released per day per heavily infected soybean plant with a planting density of 500,000 plants/ha
  • 33% of these spores were released near midday
  • 15% of the released spores were able to escape from the canopy
  • Mortality due to UVB radiation exposure in the air was proportional to cloud-adjusted surface total incoming solar radiation
  • Wet deposition of viable spores was proportional to the observed surface precipitation total

Computational Procedure

  • Model domain was divided into 14 km2 grid cells
  • NWS reanalysis 2 dataset was used to calculate the most likely downwind direction for 6 pressure levels (altitudes) at 6 hr intervals
  • Spores were moved up or down among pressure levels in accordance to the vertical component of the wind
  • Mortality due to UV exposure and rainout of spores was calculated for each time step after downwind movement
  • Deposition of spores was accumulated for all days in the calculations and is given as the number of spores per hectare

Data Sources

  • Kudzu: Raw data Daryl Jewett (USDA-APHIS) unpublished data. Kudzu map Annalisa Ariatti and Scott Isard (PSU/UIUC).
  • Soybean Acreage: NASS, 2003; National Land Cover Data, 1992; Colunga, 2004
  • Spore Deposition: Isard, S., Main, C., Keever, T., Magarey, R., Redlin, S, and Russo, J.  (2004) Weather-Based Assessment of Soybean Rust Threat to North America.  Final Report to APHIS