After heading, wheat may display white heads or prematurely dead plants in fields due to the plants being infected with root/crown rot pathogens (Figure 1). These could be mistaken for Fusarium head blight (scab) or insect damage. Inspecting plants with white heads to determine the cause may help make appropriate management decisions in the future.
The common root and crown rot diseases are take-all, common root rot, and foot and crown rot. Take-all is caused by Gaumanomyces graminis var. tritici, common root rot is caused by Bipolaris sorokiniana (synonymous with Cochliobolis sativus), while foot and crown rot is caused by several Fusarium species. Plants infected with these pathogens mature early, causing white heads and incomplete grain fill. The best way to tell these diseases apart is to peel off the outside leaf sheath cover and examine the crown and subcrown.
Take-all is characterized by a glossy, black discoloration at the base of the stem (Figure 2). Wheat fields with high incidence of take-all have circular patches of white heads or dead plants. Common root rot is less noticeable than take-all. Plants with common root rot have a discolored subcrown internode with necrotic brown lesions. Unlike take-all, plants with common root rot can be randomly distributed in the field. Foot and crown rot is characterized by reddish-brown to white discoloration of the crown. Affected white or bleached plants may occur randomly in the field but may also appear in groups or patches.
The pathogens causing root/crown rots survive on plant residues in the soil and are more common in wheat following wheat and no-till fields. Foot and crown rot pathogen can be seed-borne as well. Take all is favored by neutral to alkaline, infertile (low nitrogen or phosphorus) and poorly drained soils. Common root rot is increased when plants are stressed by drought, high temperature, freezing, and flooding. Foot and crown rot develops under dry and warmer conditions.
Plants infected with root/crown rots cannot be rescued from infection; however, knowing the occurrence of these diseases is important in managing them in the future. Crop rotation and reducing plant stress are effective in limiting root/crown rot diseases. Other cultural practices like planting in a firm seedbed, good fertility program, planting clean certified seed, and planting in warm soils also reduce the incidence of root/crown rots. Fields with history of root/crown rots may benefit from fungicide seed treatment (See: Common Root and Crown Rot Diseases of Wheat in South Dakota).