Septoria and Stagonospora Diseases of Cereals - CIMMYT ...

108
Session 6A / Session 6B — J.M. Krupinsky
diseases (S. tritici, S. nodorum, and
leaf rust [Puccinia recondita])
increased on winter wheat with
higher nitrogen rates, especially
when fungicides were not applied.
In the United Kingdom, Leitch and
Jenkins (1995) reported that
Septoria/Stagonospora disease
(principally STB) development on
winter wheat was enhanced with
the application of nitrogen
throughout the season. A wide
range of timing and splits of
nitrogen application did not
significantly influence the level of
disease severity after anthesis. Also
in the United Kingdom, Jenkyn and
King (1988) found an increase in
Septoria/Stagonospora diseases
(mostly STB) on winter wheat after
fallow compared to winter wheat
after ryegrass. They attributed the
increase in disease severity to an
increased accumulation of available
nitrogen during the fallow period.
There have also been reports of
no effect or a decrease in the
severity of Septoria/Stagonospora
diseases on wheat with increased
nitrogen rates. In Germany,
assessing disease damage by the
number of pycnidia and number of
latent infections of S. nodorum on
winter wheat, Büschbell and
Hoffmann (1992) reported that the
influence of nitrogen rates was not
significant. Also in Germany,
Tiedemann (1996) reported that
increased nitrogen reduced the
severity of SNB on spring wheat,
while increasing the severity of
powdery mildew and leaf rust.
This nitrogen effect on the disease
severity of SNB was reversed at
elevated ozone concentrations. In
the United Kingdom, late season
applications of urea solution
reduced the severity of STB on the
flag leaf of winter wheat (Gooding
et al., 1988). Naylor and Su (1988)
reported that the severity of SNB
on winter wheat was not affected
by increased nitrogen levels early
in the season and even decreased
with increasing nitrogen later in the
season.
In Maryland, USA, SNB was
reduced on winter wheat with a
higher nitrogen fertility rate (Orth
and Grybauskas, 1994). They
suggested that the reduction of
SNB was apparently due to
interference of splash dispersal of
spores in a denser canopy and the
suppressive effect of high nitrogen
fertility. In glasshouse trials, they
also reported that increased
nitrogen fertility decreased the
severity of SNB on the same winter
wheat cultivars tested in the field.
In North Dakota, USA, with a leafspot
disease complex composed
mainly of P. tritici-repentis and S.
nodorum, Krupinsky et al. (1998)
reported that with low nitrogen
levels disease severity was higher
in no tillage compared to
conventional tillage. At higher
nitrogen levels, the difference in
disease severity for tillage
treatments was greatly reduced.
In Saskatchewan, Canada, the
development of Septoria/
Stagonospora diseases on winter
wheat was influenced by nitrogen
fertility in one trial out of nine
(Tompkins et al., 1993). Greater
disease severity was associated
with low nitrogen fertility. They
suggested that lesion development
may be promoted by nitrogen
deficiency or a nutrient imbalance.
Also in Saskatchewan, Fernandez
et al. (1998) reported an increase in
disease severity with an increase in
nitrogen deficiency in dry years
with a leaf-spot disease complex
composed mainly of P. triticirepentis
and S. nodorum. Disease
severity declined with treatments
receiving no phosphorus.
Seeding Operations
A higher disease severity of STB was
associated with earlier sowings in New
South Wales, Australia (Murray et al.,
1990). The longer time between sowing
and heading probably leads to a higher
disease severity. When studying
seeding rates, row spacing, and depth
of seeding in Pennsylvania, USA,
Broscious et al. (1985) reported that
increased seeding rates increased SNB
in four out of 13 trials and decreased
SNB in one trial. They suggested that
growers could reduce row spacing from
18 cm to 13 cm to increase yields
without increasing disease severity. In
Saskatchewan, Tompkins et al. (1993)
reported that the severity of Septoria/
Stagonospora diseases increased with a
higher seeding rate. Disease severity
was not influenced by row spacing.
Narrow row spacing (10 cm) with
increased nitrogen rates reduced SNB
on winter wheat and increased yields in
Maryland, USA (Orth and Grybauskas,
1994).
Use of Disease-Free Seed
Seed infected with S. nodorum can be
a source of primary inoculum and a
probable source of transmission from
one wheat crop to the next. Inoculum
can survive in seed for extended
periods of time. Septoria tritici can be
seed-borne but is not a significant
source of inoculum (Eyal, 1981; King et
al., 1983; Shipton et al., 1971). Although
the use of disease-free seed may not be
considered a cultural practice, it should
be evaluated by the producer as a
management practice for reducing
disease severity. Cultural practices such
as crop rotation may not be effective if
seed infected with S. nodorum is used
for planting (Luke et al., 1983). The
beneficial effect of disease-free seed can
be negated by sowing into residue from
a previous wheat crop (Luke et al., 1983,
1985; Milus and Chalkley, 1997).