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Field and Forage Crops |
Soybean rust, a potentially devastating disease of soybeans, was first discovered in the continental United States last year in Louisiana. Shortly after this first detection, the disease was also confirmed in Alabama, Arkansas, Florida, Georgia, Mississippi, Missouri, South Carolina, and Tennessee. So far in 2005, soybean rust has been found in Florida and in the southwest corners of Georgia and Alabama.
Several fungicides have been approved for use against soybean rust. Some are to be applied prior to disease detection to help prevent disease development while others have some curative qualities, to help check the disease after it has already infected the plant. While it is the grower's decision as to when to begin application of these fungicides, the North Carolina Department of Agriculture and Consumer Services and the North Carolina Extension Service recommend that applications of the preventative products not begin until there is a reasonable threat of the disease in North Carolina.
Prudent use of these fungicides is important for several reasons. First, the number of applications that can legally be applied to soybeans is limited. Therefore, every application needs to count. Second, just like with any other pesticide, unnecessary use needlessly increases pesticide levels in the environment and can encourage resistance development (shortening the useful life of the product). Third, fungicides can be expensive.
There are several web sites devoted to providing soybean rust information. Topics such as disease tracking, scouting, identification, control options and contact information can be found at these sites. The information provided at these sites can help growers make informed decision regarding fungicide applications. Some useful soybean rust web sites include:
http://www.stopsoybeanrust.com/mc_home.asp
http://www.sbrusa.net
http://www.usda.gov/soybeanrust
http://www.epa.gov/oppfead1/cb/csb_page/updates/soybean_rust.htm
http://www.ces.ncsu.edu/depts/pp/soybeanrust/index.php
In addition to these web sites, growers can also obtain information from their local Extension office and from Extension personnel located at North Carolina State University. Dr. Stephen Koenning, Research Assistant Professor and Extension Specialist with the Department of Plant Pathology at North Carolina State University has been, and continues to be, greatly involved in scouting for this disease in North Carolina and providing growers guidance on how be prepared should it reach our state. Dr. Koenning can be reached by electronic mail at stephen_koenning@ncsu.edu or by telephone at 919-515-3905.
Sentinel plots continue to be monitored weekly and several samples from kudzu, taken in the southern part of the state, were sent to the lab for examination. All were negative for Asiatic soybean rust and rust has not been found in North Carolina thus far. Brown spot caused by Septoria glycines has been detected in numerous locations and in some instances has resulted in defoliation of the lower portion of the plant. Similarly, soybean downy mildew is also quite common this year. Neither disease ordinarily requires management. Target spot caused by Corynespora cassicola has been identified in Wilson, Perquimans, and Alamance counties and this disease does warrant attention.
Recent weather associated with hurricanes may have transported Asiatic soybean rust to North Carolina, but the numbers of spores would be very low. For more information, see the following web site: http://www.ces.ncsu.edu/depts/pp/soybeanrust/index.php. Fields should continue to be scouted for foliar diseases, including rust, frogeye leaf spot, and target spot. Scouting efforts should be intensified in about 2 to 3 weeks as more soybeans enter the reproductive stage and infections that may have occurred this past week may then be evident.
It seems likely that soybean and kudzu have latent infections of soybean rust in the mid-South and Delta. The amount of spores that may have been transported to the mid-South with hurricane Dennis was estimated as being very low. It will probably be 3 to 4 weeks before rust is evident in those areas, and can begin serving as a source for North Carolina.
A commercial field in Baldwin County, Alabama has fairly severe rust infections at this time and will likely be sprayed with fungicides. There are reports of Asian soybean rust-like spores being found in spore traps in Tennessee and Kentucky. It is not possible at this time to say that these spores are Asiatic soybean rust. There are hundreds of rust fungi in North America and spores look very similar.
A fungal disease, target spot of soybean caused by Corynespora cassicola, was identified on three samples sent to the Plant Disease and Insect Clinic at North Carolina State University. In 2004, this disease caused early defoliation of certain soybean varieties and resulted in yield losses of as much as 50 percent. At this time we suspect that only a few varieties are susceptible to this disease. When submitting samples, please specify the variety, as this helps us keep track of which varieties are susceptible. The use of a foliar fungicide may well be warranted on susceptible varieties. Please consult the online version of the North Carolina Agricultural Chemicals Manual for recommendations for fungicides.
Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Last modified on July 18, 2005 by Stephen J. Toth, Jr.