Soybean Rust Exploded in October

We have seen this year in corn how weather can impact diseases. The same could be said about soybean rust (SBR). What a difference a few weeks and the proper weather conditions can make with this new invasive soybean disease. Since October 1st, 175 new counties have tested positive for SBR in the southern and most recently the midwestern United States as well. The majority of these finds are on late season soybeans and or double crop beans. On October 26, SBR was found on soybeans in LaFayette, Indiana (home of Purdue University). Lafayette is 165 miles south of Chicago and this represents the most northernly find of SBR in the US ever.

The total numbers as of November 7 (midnight) for this year's soybeans are 227 different counties in 15 states and if you include Kudzu the number increases to 256 counties over those same 15 states. The latest spread of SBR from Louisiana up the Mississippi river and the Ohio River Valley can be attributed to the prolonged stormy weather that occurred in late September that brought persistent rain showers/thunderstorms into Ontario and the Midwestern US. Agriculture and Agri-Food Canada and OMAFRA are examining rainfall spore trap collectors that we have established in the Province to determine if these spores arrived into Ontario on these events.

A similar situation occurred along the eastern US seaboard following Hurricane Ernesto. The rains that were associated with Ernesto provided the needed moisture conditions necessary for SBR development from Florida through to the Carolina’s and the Virginia’s.

The good news for Ontario and Canadian soybean producers is that the monitoring sentinel plot system that has been established in North America and which Ontario has been participating in through funding by Agriculture and Agri-Food Canada through the Agricultural Adaptation Council's CanAdvance Program, the Ontario Soybean Growers and the Ontario Soybean Rust Coalition works. Not only was soybean rust able to be detected at levels as low as one lesion/pustule per 100 leaves examined but the computer prediction models for soybean rust were able to predict the movement of SBR spores out of Louisiana into the upper Midwest.

This shows the importance and effectiveness of the SBR sentinel plot system and does provide an effective decision support tool for producers and advisors when it comes to managing this very destructive disease.

These most recent events could have an impact for us in 2007 if the weather predictions for a mild winter is true for the southern US. Every winter more and more kudzu (the overwintering host) is being infected and ultimately the millions of kudzu area in the extreme south will provide a significant number of spores for potential spread north. What this means is that the early spring conditions in the southern US will become even more important as we have seen over the past two years. SBR movement into the north has been delayed by hot, dry conditions in the south. The events of the past month have shown us that unfortunately under favourable weather conditions SBR can move vast distances and cover much of the soybean production areas of North America.

Figure 1. Soybean Rust Observation - November 7, 2006

(text equivalent of graphic)

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