For Release November 14, 2004

Soybean Rust Disease Now in the United States

by Chuck Otte, Geary County Extension Agent

We knew it was going to happen eventually. Soybean rust had moved from its native Asia to southern South America and then this summer it was found in South America north of the equator. Of course, then we had to have a wonderful series of tropical storms that constantly swept air masses from northern South America across the Gulf of Mexico. So it is probably no surprise that late last week, soybean rust was found on soybean plants in research plots in Louisiana.

One of the real advantages of growing soybeans is that we historically have not had to worry about insect or disease pests, to speak of, with the crop. Any problems were generally minor in nature and easily dealt with. In fact many of the diseases were often associated with drought stress so we had far more losses from lack of moisture than from pests. Plant the soybeans, apply some fertilizer, maybe, keep the weeds controlled and harvest the crop.

There are two races of soybean rust. As luck, or bad luck, would have it, the race that was found in Louisiana was the more aggressive and destructive race. Soybean rust can be controlled with judicious use of several fungicides. But fungicides cost money and take profit out of your pocket.

Like many of the rust diseases, we expect soybean rust to not overwinter in Kansas but to blow in every year on southern winds. It likes humid weather with rainfall, think of wheat rust, so hot dry summer conditions are going to be a detriment to this pathogen. If it does get established and goes untreated, it can completely defoliate a plant in 10 to 14 days. The rust can infect leaves and pods. Untreated infestations will obviously lose yield through loss of leaf area and dying pods.

We do not yet know what to expect from this disease in Kansas. Since this has not been a concern for soybean production in the USA before, it is doubtful that we have much resistance to the disease in any of our varieties. If we consider normal Kansas summer weather conditions, we would anticipate it being the worst in southeast Kansas and becoming less of a problem as we move north and west. It also tends to favor cooler damper weather so we would expect it to be more of a late summer problem, probably September and October. This is to our benefit because in most years our soybean plants are starting to shut down by early September except on the longer season varieties that are typically grown in the southeastern part of the state. But if you think back to this growing season, June and July could have been highly favorable to this disease. This would be the worst case scenario!

What do we do now? During the winter K-State and USDA will be gearing up with a lot of educational information. Look for this in your mailbox and printed ag media sources. A good webiste exists at EPA had already started registering several fungicides for use on soybean rust in anticipation of the disease arriving so there will be tools to battle the disease. I would not start making drastic plans to move away from soybean production. But it does point out the need to keep a balanced mix of crops in your production plan. What it definitely means is that soybean production in the United States has just entered a whole new phase!


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