The wheat book : principles and practice - Department of Agriculture ...

CHAPTER 10 – DISEASES THE WHEAT BOOK
OCCURRENCE, RECOGNITION AND CONTROL (continued)
Pythium root rot
Occurrence
Pythium root rot (Pythium spp.) is most common in
areas of high rainfall. Very little is known about the impact
of the disease on crops in Western Australia. It is more
likely to occur during wet years especially if it is very wet
after the break of the season and the crops have just been
sown.
Recognition
Plants are stunted, develop poorly and generally look
unthrifty and nitrogen deficient. These plants may have
reduced tillering and may die within the field. Plants can
occur individually throughout the crop or may occur in
patches where the soil is waterlogged.
The root system is stunted (looks stubby) with very few
lateral roots present. The roots are soft and yellow to light
brown in colour.
Control
There are no resistant varieties to the disease. A short
rotation with a legume or pulse crop will not reduce the
level of disease as the fungus survives as oospores in the soil
for over 5 years. Pythium exists mainly in the top 10-15cm
of soil where fine wheat roots are abundant, and where
crop residues are deposited. These residues provide
nutrients and moisture to the fungus.
Most crop damage occurs when rainfall is high after
sowing. The disease is more severe in direct drilled crops
and where stubble is retained. Avoid sowing into cold wet
soils, or sowing crops directly after applying herbicides to
control grass weeds.
Increase soil fertility. Plants may recover from early
infection where nutrition is adequate to promote root
growth. Studies in Canada have shown that the disease is
worse in crops that have phosphorous deficiency.
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