Figure 1. Thin stand in a wheat field due to root and crown rot.
Photo: E. Byamukama
Winter Wheat Scouting: Crown & Root Rots
Some winter wheat fields scouted last week had patches of thin plant stands (Figure 1). Poor plant stands can be attributed to low soil moisture and winter kill due to lack of snow cover or crown and root rots. Determining the cause of the poor plant stand may help inform management decisions for the future wheat crop.
One way to tell if the poor wheat stands are a result of crown and root rots is to gently dig the plant and examine the crown, subcrown and the roots. Plants that have root rot may have a discolored sub-crown and crown (Figure 2). Plants may also have rotted root surfaces and sometimes the roots will be clipped.
Figure 2. A wheat plant with discolored subcrown, a symptom for common root rot. Photo: E. Byamukama
Causes & Symptoms
The root and crown rots are caused by fungal pathogens namely Rhizoctonia spp (causes bare patch), Fusarium spp (cause Fusarium foot and crown rot), Bipolaris sorokiniana (causes common root rot) and Gaumanomyces graminis var. tritici (causes take-all). These pathogens survive in crop residues. Infection by these pathogens can lead to reduced tillering and stunted growth. Sometimes crown and root rot symptoms are masked until wheat heading, where bleached heads can be seen.
Plants infected with root/crown rots cannot be rescued from infection; however, knowing the occurrence of these diseases in the field is important in making future root and crown rot management decisions. 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 the 2017 South Dakota Pest Management Guide: Wheat for more tips.