White Rust (Albugo candida) – Seedborne
Symptoms first appear as light green spots that
turn white and eventually develop into white,
raised spore masses called pustules. Pustules,
which may appear on upper or lower sides of
leaves, contain white, wind-dispersed summer
spores that can lead to additional infections. Some
infections can become systemic, leading to the
formation of galls, especially if the tissues of
plants are very young. In flowering radish crops,
A. candida causes bizarrely distorted seedpods,
termed ‘stagheads’ (galls on infected seedpods).
Stagheads significantly reduce seed yield and
quality. Overwintering, resting spores of the
pathogen (oospores) are produced in diseased
tissues including the stagheads. Small pieces of
stagheads can contaminate harvested seed and act
as a source of inoculum. Oospores can also be
seedborne. Disease progression is slowed by
extreme hot or cold temperatures and by dry
weather. In contrast, the disease increases quickly
during mild periods with intermittent rains, heavy
dew, and/or fog. Destroy crop residue and
cultivate fields prior to planting to destroy all
volunteer plants. Avoid planting in fields near
other cruciferous cropsHot water can be an
effective seed treatment.