Thursday, November 8, 2007 - 8:30 AM
333-1
Soybean Rust - What Have We Learned after Three Years?.
Phakopsora pachyrhizi, the Asian soybean rust (ASR) pathogen, does not survive in the absence of living host tissue. This would be the end of the rust story except that the pathogen has a very large host range, so-called alternative hosts, including kudzu, which is widespread in the southern U.S. At first it was feared that the disease would be initiated every year from infected kudzu, but, fortunately, this plant is susceptible to freezing temperatures, and re-infection from distant inoculum sources (south Florida and south Texas) has been delayed until late spring during the past 2 years. However, if the freeze line remains further north, it is likely that ASR will get a jump start on the soybean crop. Also, even though ASR was found on kudzu in June, 2006, it did not spread into the commercial crop until much later in the summer because of the drought. Normal rainfall patterns probably will affect the rate of spread, not only within the Gulf South but also further north. The sentinel plot program, which was established throughout the eastern U.S., is an unprecedented effort for early disease detection, and it has served its purpose well. Its primary value to date has been to confirm to diagnosticians and others that ASR has not been a threat in specific areas, and fungicide spray recommendations were not implemented. While ASR is a destructive disease, it is readily controlled with several fungicides with at least two modes of action. However, the disease is extraordinarily explosive, and once it starts it is very difficult to control. Thus, until disease forecasting models have been perfected, reliance upon sentinel plots and intensive and frequent scouting are essential to the management of this disease. A sophisticated website, www.sbrusa.net, that provides information on occurrence, likely high risk areas, and current recommendations, has been invaluable in keeping the entire soybean industry updated on a daily basis.
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