Soybean Disease Update – September 23, 2011

Bob Mulrooney, Extension Plant Pathologist;

Soybean Vein Necrosis Virus
I just wanted to add a brief summary for our WCU readers that soybean vein necrosis virus has been seen in all three counties in Delaware and apparently is widespread in the surrounding states of PA, MD, and VA. We see it everywhere we look now but I am not sure how much effect it is having on yield at this point. Researchers in other parts of the country are also working on it and have a few more years experience with it. It is premature to say too much about it other than we now know what is causing the symptoms we have seen this year and probably last year as well, but did not know what it was. By the time the winter meetings occur hopefully I will be able to share more hard facts about the disease and control options for our region.

Early symptoms of soybean vein necrosis virus (SVNV) from DE

Soybean Cyst Nematode
Do not ignore soybean cyst nematode. Soil sampling after harvest before any fall tillage is recommended for fields to be planted next season to soybeans following this year’s crop. Do not plant SCN susceptible varieties without soil testing first. Soil sample bags and information sheets are available from the county Extension offices for $10/ sample bag.

Soybean Rust Risk Assessment (ZedX, Inc. & PSU)
Despite recent heavy rainfall along the Atlantic Coast and throughout the Northeast from the remnants of Lee and Hurricane Irene, source inoculum in the Southeast was likely still too low to cause widespread transport and deposition of spores further north. Soybean rust was, however, identified in extreme southwestern Georgia for the first time this season. Due to the ongoing drought in Texas and Oklahoma, the slow progression this season in the Southeast, and the fact that the primary soybean production season is in the later stages, it is unlikely that soybean rust will spread as far as it has in years past. As such, the risk area will remain rather minimal in spacial coverage (see map below). Double crop soybeans along the Gulf Coast could still be at risk for soybean rust as the season progresses, but even double cropped soybeans are at a minimal risk.

The above image displays the current threat level of soybean rust. The yellow “wait” areas are considered slightly at risk, orange “watch” areas are at moderate risk, and red “warn” areas are at great risk or already identified positive for soybean rust. Risk areas are estimated based on meteorological factors affecting spore transport and deposition and factors conducive for further development within the canopy such as temperature and moisture. Biological factors such as host plant and crop phenology are also considered. Risk assessment maps are produced by the PSU Ensemble Field Crop Rust Forecasting Program.

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