Visual symptoms of soybean cyst nematode (SCN) are showing in soybeans:
Not all fields will have this degree of chlorosis and stunting (above picture), this is a severely infested farm and a non-resistant soybean. More often symptoms are much more subtle. In the picture below the farm is moderately infested with SCN (manageable levels) on the left is non-resistant soybean and on the right is a resistant soybean. Notice the slight differences in growth.
More on SCN management:http://www.extension.umn.edu/agriculture/soybean/soybean-cyst-nematode/