Wheat should be planted after soybeans not after wheat or corn. Diseases are a big concern in wheat after wheat. One such disease, and by far one of the most important, is head scab. The head scab fungus survives in wheat stubble left in the field after harvest. Wheat planted into this stubble is more likely to have head scab and vomitoxin problems next year, especially if late-spring, early-summer conditions are wet and humid. Our studies have shown that when wheat (or corn) residue is abundant (more spores of the fungus present), only a few days of wet and humid conditions during flowering are needed for head scab to develop and vomitoxin to exceed critical marketing thresholds (2 parts per million). For the same reasons, planting wheat after corn is just as bad as planting wheat after wheat. The scab fungus survives equally well in both corn and wheat stubble.
In addition, growers who plant wheat after wheat usually have more problems with diseases such as Cephalosporium stripe and Take-all root rot. Plants severely infected in the fall and winter will become weak and discolored in the spring and often die prematurely without producing grain. In addition, foliar diseases such as Stagonospora leaf blotch, Septoria leaf blotch, powdery mildew, and tan spot become more problematic when wheat follows wheat. These diseases are all caused by fungi that survive in wheat stubble left in the field, and as such, can readily attack the new crop and spread shortly after germination or early in the spring. When diseases become established early, growers are more likely to suffer higher yield and quality losses