Black root (Aphanomyces raphani)
The disease appears as brown to bluish-black
discoloration in cracks or wounds on the side or
top of roots. Root growth slows as symptoms
progress; diseased roots become increasingly
black and may cause girdling of the entire root.
These black areas of discoloration extend inward
in radial streaks. Choose planting sites with good
drainage and avoid over-watering. Practice good
field sanitation. Varieties vary in susceptibility,
with ‘White Icicle” being very susceptible. A.
raphani is not seedborne, but resting spores of the
pathogen can be moved in mud on tires or other
equipment, and in trash or dirt in poorly cleaned
seed.