2005 Year in Review

Scouting and Sampling for Soybean Rust

By now, those involved with production agriculture know that Asian soybean rust was confirmed for the first time in the continental United States in November 2004. Soybean rust is a fungal disease that infects leaves, stems, petioles, and even cotyledons of the plant and can cause defoliation and significant yield loss. This article will address scouting and sampling guidelines for the disease.

The soybean rust that was detected in Louisiana was Asian soybean rust, the more aggressive species, not the relatively mild American soybean rust. If rust appears in a soybean field, how can one tell these two species apart? In short, one can’t. The species must be identified and differentiated in a designated plant diagnostic laboratory.

Illinois has developed a state plan to respond to soybean rust and it is available online at Soybean Rust Program. Early detection and identification of the disease is critical in making soybean rust management decisions. When scouting or monitoring fields for the disease, one must look at the lower quarter of the plant and be sure to examine the undersides of leaves.

The general guideline is to examine 20 plants in five random locations per field weekly. University of Illinois currently recommends determining incidence rather than severity for scouting. For example, one plant with any amount of rust in 100 plants is 1% incidence. Those scouting for soybean rust should have a land lens at 10-20x. This will enable one to see the rust pustules (appear similar to a small “volcano”, topped with a pore through which spores are released).

If one finds “suspect” symptoms, collect 20 leaflets with the symptoms. The leaflets should be flat, dry, and placed between dry paper toweling. Leaflets should be packaged in two layers in zip lock plastic bags. The bags should be identified with the date, host plant, collector’s name, phone number, collection location within the field, location of the field, county, township, and section, plus the nearest intersection. GPS information is also helpful.

Immediately submit samples to the University of Illinois’ Distance Diagnostics through Digital Imaging (DDDI) system. If the sample cannot be immediately shipped or delivered, keep refrigerated until shipment. DDDI sites are maintained at all Extension unit offices across Illinois. Digital images of samples will be submitted for you by the Extension unit office. The diagnosis will be emailed back to the unit office. The results of your soybean rust prescreening via DDDI should be available within a few hours. If the DDDI prescreening appears suspect, your plant sample will be submitted via overnight mail to the University of Illinois Plant Clinic.

Numerous workshops this winter will address soybean rust. Additional information and material is available at the Extension unit offices.

by  Editor, theCity1.com
January 21, 2005