Aphanomyces Root Rot

Aphanomyces cochlioides

 

Identification

  • Aphanomyces is caused by a fungus in the soil
  • The fungus will overwinter in the soil as spores contained with residual plant debris
 

Cause of Infection

  • Under wet, warm conditions, oospores germinate to produce mobile zoospores
  • These spores swim in the water in the soil and infect the sugarbeet root
  • Infection can occur at anytime throughout the growing season, but the optimal soil temperature range is 68° to 86° F
  • Infections do not occur at temperatures less than 60° F
 

Detection

  • Aphanomyces can infect seedlings and mature roots
  • At the seedling stage, the hypocotyl and root rapidly turn black and shrink to a dark thread
  • The chronic infection, which occurs later in the growing season, manifests itself as root distortion and dark colored scarring
  • This disease is often confused with another root rot (Rhizoctonia crown and root rot, RCRR).  The two can be differentiated by foliar symptoms, which are less severe when caused by Aphanomyces.  Wilting is severe and permanent with RCRR and results in dark black leaves collapsed around, but still attached to the crown.  Aphanomyces root rot rarely causes wilting unless there is water stress as well.  Under severe conditions, leaf scorching can occur.  The root symptoms with RCRR are also much more severe ranging from dark, wet lesions to a dark, wet rotting of the entire root; both usually originate at the crown or in some cases the root tip.
 

Identification

  • Young seedlings may dampen off and reduce stand
  • Young seedlings are weak and are more susceptible to the wind
  • Sugarbeets that have been infected late in the growing season often survive, but when foliage is removed at harvest rotted roots are easily dislodged or are too small to be harvested
  • The roots will have reduced yield and sugar content and will store poorly
 

Control

  • Select varieties with resistance; only effective control for chronic stage infection
  • Plant Tachigaren treated seed  to prevent seedling disease
  • Plant as early as possible
  • Cultivate to keep the soil dry
  • Improve field drainage
  • Increase the length of rotation
  • Control weeds
  • Avoid the spread of contaminated soil