West Virginia Department of Agriculture (8/01/08)

Plant Industries Division

Market Bulletin Article

August Issue

 

Norman Dart

Agricultural Plant Pathologist

 

Agricultural Plant Pathology Survey Updates- Soybean Rust

 

The 2008 plant pathology survey season is well underway in West Virginia.  With support from the United Stated Department of Agriculture, the West Virginia Department of Agriculture (WVDA) is surveying for three high-risk plant diseases this growing season including, Soybean Rust (SBR), Karnal Bunt (KB) and the Potato Cyst Nematode (PCN). All three pose a threat to crop health and in the case of PCN and KB could have major trade implications if introduced on a large scale throughout the state. In this article we’ll give you an update on our SBR survey efforts and the disease outlook for this season. In following Market Bulletin issues we’ll update you on the other two surveys.

 

Soybean rust caused by, Phakopsora pachyrhizi is a foliar disease which has impacted soybean production in Asian countries for decades and has more recently spread to South Africa and South America. SBR has only been found in the U.S. since November of 2004. Before this introduction, North America was the only continent that produces soybeans where SBR had not been introduced. The main cultivars of soybean grown in the U.S. are thought to be very susceptible to SBR. Fortunately, the disease can be controlled with fungicides so the impacts of the disease can be mitigated until resistance is bred into cultivars that are well suited for North America.

 

Soybean rust is an obligate parasite which needs a living host to survive. In North America, after Soybean fields are harvested Kudzu is thought to serve as the alternate host that allows the rust to overwinter in southern states such as Florida and Louisiana. In more northern states such as Ohio and West Virginia, Kudzu dies down during the winter killing the pathogen. Spores of the pathogen must spread north via winds each growing season making it harder for SBR to infect plants early enough in the growing season to have an impact on crops in a state as far north as West Virginia.

 

Although SBR has never been detected in West Virginia, the disease is new to North America and plant pathologists are still uncertain of how far and fast it can spread north in a given season. In 2007, soybean rust spread as far North as Virginia and as of July 2008, SBR has been detected in spore traps on the Virginia-West Virginia boarder. As of July 10^th, infected plants have only been observed as far north as southern Georgia. We are working hard to ensure that if this disease does take hold in West Virginia this season that we will detect it early enough for growers to respond. Early symptoms of soybean rust appear as yellow to brown flecking on leaves in the lower canopy. The lesions look like several other diseases such as bacterial leaf blight and Septoria leaf spot. The key to distinguishing SBR from other diseases is looking for volcano-shaped pustules on the lower surface of the leaves which can be seen with a magnifying glass under a trained eye.

 

Currently the WVDA is monitoring 9 soybean fields in Wood, Boone, Berkeley, Jefferson and Hardy Counties and 1 Kudzu plot in Boone County for SBR. You can see a map of the Counties being surveyed in West Virginia and find links to diagnostic guides on the national SBR website: http://sbr.ipmpipe.org/cgibin/sbr/public.cgi. If you find SBR-like symptoms in your soybean field please call the state plant pathologist at (304)558-2212 (ext. 3720) to schedule a field visit.

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