Septoria and Stagonospora Diseases of Cereals - CIMMYT ...

Differences in weather cycles in
wheat growing areas are often
dramatic, which may account for
some of the differences in the
impact of diseases described in the
literature. When comparing tillage
effects in northeastern North
Dakota, USA, Stover et al. (1996)
observed that different diseases
dominated each year with different
weather conditions. They found
that P. tritici-repentis dominated in
the first two years of the study, and
septoria foliar diseases and
fusarium head blight dominated in
the third year.
Tillage or lack of tillage can also
affect the severity of individual
diseases. Sutton and Vyn (1990)
reported that P. tritici-repentis and
S. nodorum were promoted when
wheat was grown after wheat and
minimum or no tillage was used,
whereas S. tritici was suppressed.
The reverse occurred when wheat
followed alternative crops in all
tillage treatments or following
wheat under conventional tillage.
With airborne ascospores of S.
tritici implicated as the source of
primary inoculum in Oklahoma,
USA, Schuh (1990) concluded that
the amount of residue after
different tillage operations did not
have a strong effect on disease
severity.
In western Canada, Bailey and
Duczek (1996) indicated that foliar
diseases increase under reduced
tillage but not always to damaging
levels. With conditions for low
disease development, Bailey et al.
(1992) did not observe consistent
tillage effects on foliar diseases. In
Kentucky, USA, Ditsch and Grove
(1991) reported that SNB was not
affected by tillage but powdery
mildew infection (Erysiphe
graminis) was higher under no
tillage. In North Dakota, USA, with
a leaf-spot disease complex
composed mainly of P. triticirepentis
and S. nodorum, Krupinsky
et al. (1998) found generally higher
levels of necrosis and chlorosis
associated with no tillage
compared to minimum or
conventional tillage. However, in
some trials the tillage effect varied
depending on the nitrogen
treatment. With a leaf-spot disease
complex composed of P. triticirepentis,
B. sorokiniana, and S.
nodorum, Reis et al. (1992, 1997)
reported that disease incidence and
severity were higher with
minimum and no tillage treatments
in Brazil. In the eastern USA, both
tillage and crop rotation are
recommended to avoid losses to
SNB (Cunfer, 1998; Milus and
Chalkley, 1997).
Burning of Residues
Although burning crop residue
was recommended in the past
(King et al., 1983; Shipton et al.,
1971), it is no longer recommended
because of environmental concerns.
In addition, burning may not be
hot enough to eliminate all residue,
leaving sufficient infested residue
to provide carryover of inoculum
for another wheat crop (Eyal, 1981).
In northeastern North Dakota,
USA, Stover et al. (1996) compared
chisel plowing (high residue) to
moldboard plowing and burning
followed by moldboard plowing.
The effect of chisel plowing on
early season foliar disease did not
consistently carry over to late
season severity ratings. In the first
year, chisel plowing resulted in the
highest late season disease severity,
in the second year, there were no
differences, and in the third year,
the chisel plow treatment had the
lowest late season disease severity.
Influence of Cultural Practices on Septoria/Stagonospora Diseases 107
Overall, yields were not affected by
a tillage (burning)-related foliar
disease effect.
Plant Nutrition: Nitrogen
Fertilizer
As with other management
practices discussed above,
environmental conditions influence
disease development and treatment
responses, leading to variation in
research results among different
geographical regions. The severity of
Septoria/Stagonospora diseases may
increase or decrease with increasing
nitrogen rates depending on the
region. Tiedemann (1996) suggested
that inconsistencies of Septoria/
Stagonospora disease response to
nitrogen fertilization may be due to
in part to environmental factors such
as ozone.
High rates of nitrogen fertilizer
have been reported to increase the
severity of Septoria/Stagonospora
diseases. In addition, increased
nitrogen can increase the danger of
lodging and delayed maturity
(Shipton et al., 1971). In
Pennsylvania, USA, Broscious et al.
(1985) reported that the severity of
SNB and powdery mildew increased
significantly on winter wheat as the
rate of spring applied nitrogen
fertilizer increased. Similarly, Ditsch
and Grove (1991) in Kentucky, USA,
reported that SNB and powdery
mildew were lowest on winter
wheat at the zero nitrogen treatment
but increased as nitrogen rates
increased. In New York, USA, under
conditions of low disease severity,
Cox et al. (1989) suggested that high
rates of nitrogen have the potential
to increase yield and foliar disease
severity on winter wheat in the
northeastern USA. In Tennessee,
USA, Howard et al. (1994) reported
that the severity of three foliar