The picture (above) is from a field in Linn County with sudden death syndrome. The leaf tissue becomes yellow and brown between the veins, with the main veins remaining green. The foliar symptoms of brown stem rot can be the same as sudden death syndrome. The best way to tell these two apart is to split the stem lengthwise near the ground and check the center of the stem (pith). The pith will still be white with sudden death, but will be hollow or brown with brown stem rot.
I have not seen many problems with foliar soybean diseases so far this year, but I have seen soybean sudden death syndrome in most fields that I have been in this past week in eastern Iowa. In most fields the disease is evident in small areas, but the size of the areas is growing in some fields.
The disease is caused by a soil borne fungus and the infection of the plants actually occurred early in the growing season. The disease is not actually spreading from plant to plant as it may appear. Early planting in cool wet soils and flooding during the vegetative stages will increase the problems with this disease. Although early planting was not common this year, the excess rain that many areas of eastern Iowa received in May and June has likely increased the incidence of this disease. It also is usually seen more in areas where there is some soil compaction or areas needing tile drainage. Usually soybean cyst nematode is also present in fields infested with sudden death syndrome. Planting varieties with soybean cyst nematode resistance as well as varieties that are more tolerant to sudden death can help reduce the problem. Also it is more likely to show up in the future where it has been seen in the past, so planting those fields last can also improve the chances of escaping the disease.
White mold is also showing up in some fields, but is not as widespread as sudden death syndrome. Soybean aphid numbers are now decreasing in some fields, but are still increasing in others. It may still pay to spray fields where aphid numbers are increasing and have reached the 250/plant economic threshold (& 80% of plants infested), as long as the field has not yet reached R6 (full seeds in one of the 4 upper nodes).