Root And Crown Rot Showing Up In S.D. Wheat Fields

By Ruth Beck

SDSU Extension Agronomy Field Specialist

The recent high temperatures resulted in premature ripening of wheat fields in central South Dakota and also in the appearance of sporadic white heads occurring in some of those wheat fields. White heads (with heads that did not fill) or prematurely dead wheat plants may be the result of plants infected with root/crown rot pathogens (Figure 1).

Little can be done to remedy the premature ripening, however inspecting plants with white heads to determine the cause may help with future management decisions. White heads can also be caused by insect damage or Fusarium head blight (head scab).



Figure 1. A wheat field with foot and crown rot in Stanley County. Photo by R. Beck.
 
Pathogens & Diseases

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. 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 (Figure 2).

Figure 2. Plants suspected to have crown and foot rot infections. Photo by R. Beck.

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 favors 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 warm, dry conditions.