2005 Year in Review

Soybean Rust Questions Aren’t Easily Answered

Soybean growers are being inundated with meetings and printed information about soybean rust. On occasion, I have heard individuals express frustration that the experts on this disease are not able to provide definitive answers on exactly what to expect next summer, and how events will play out. Their rationale is that the disease has been present and studied in South America and Africa for a number of years, therefore, we should know by now exactly what to expect here.

Unfortunately, communicable plant diseases are caused by biological organisms that don’t always respond in a predictable manner. There are four things required for disease infection and progression to occur. You must have a susceptible plant host; the disease pathogen must be present to infect the host; the environment must be ideal for infection to be successful; and a period of time must elapse while infection occurs and spreads.

Researchers currently have three of the four pieces of information needed to make accurate predictions. We know that all commercial soybean varieties are susceptible to the disease. We know that the disease organism is now found in the continental U.S. Once a given plant is infected, we know how long it takes the disease to develop and spread if temperature and moisture conditions are ideal. What we don’t know, and can’t predict with accuracy, is how our environment will affect this process.

Soybean rust will not survive winter temperatures in the Midwest, therefore, the fungal spores will have to blow northward from over-wintering host plants in the Gulf Coast states. When, and to what degree this occurs, will be influenced by the level of early infection of alternate hosts in the south, and the weather patterns that occur this spring. When and if fungal spores reach the Midwest, the speed and progression of the disease will depend upon our local growing conditions at the time.

The experiences gained from studying South America and Africa do not translate well to our growing conditions. Those countries have humid and tropical environments that are more conducive to the disease. In areas of China where growing conditions may be more similar to ours, there is a mountain range present that affects the wind patterns that would blow fungal spores northward from their over-wintering sites. As a result, we don’t have good comparisons on how the disease may move northward and spread here in this country.

Unfortunately, we will have to learn from experience under our unique set of environmental conditions. Successful management begins with keeping abreast of news reports of how far and fast the disease is progressing this spring. Fungicides that are effective at controlling the disease and reducing yield losses are available. Diligent scouting of your fields will be required to know when infection occurs, so that the proper control treatments can be applied in the most efficacious manner. Attend educational meetings this winter; learn how to identify the disease and the proper method to treat it if and when it does occur.

by  Editor, theCity1.com
February 11, 2005