October, 2004
Research summary
- Fungicide experiments
clearly demonstrated that many leaf diseases on cereals
could be economically controlled by using off-patent
fungicides. However, the degree of disease control achieved
by a particular fungicide varied with the type of disease
present in the target crop.
- Most presently available
triazole fungicides are effective for controlling
leaf rust and powdery mildew in barley. Triadimefon
was most cost effective.
- Early season management of
barley powdery mildew is recommended.
Fungicide seed dressings should be used routinely for
susceptible barley varieties in medium rainfall
environments. Fungicide applied in-furrow at seeding can
provide longer season control, especially in environments
with longer growing seasons. Where early season control was
not practised, foliar fungicide sprays with triadimefon or
propiconazole effectively reduced severity and increased
yield.
- Spot-type net
blotch is more difficult to control. Propiconazole
was the most cost effective fungicide. Recommended
application rates of 250 or 500mL/ha at late stem elongation
stage (Z37) resulted in 17 to 32 per cent yield increases
and improved grain quality in crops with ≥ 3 t/ha yield
potential. Lower yielding crops would also benefit from
controlling this disease when it is present during stem
elongation or early flag leaf emergence.
- Wheat leaf rust
and powdery mildew can be economically controlled
by triadimefon. Foliar fungicide tebuconazole (Folicur
430SC) was more effective than in-furrow fungicides (Impact
250SC or Triadimefon 500WP) in controlling septoria nodorum
blotch. Stem rust can also be controlled by tebuconazole.
- The time of onset of
disease epidemic in crops had a major influence on the
efficacy of fungicide disease control, especially for barley
and wheat leaf rust. Disease onset at early stem elongation
stages required two applications of fungicide to achieve
adequate control in susceptible crops. However, epidemics
that developed after flag leaf emergence needed a single,
well-timed, fungicide application to prevent further yield
losses.
- Where an early outbreak of
leaf rust in wheat occurs, the initial
triadimefon spray should be applied at early stem elongation
(around Z31) and followed with a second application at flag
leaf emergence (Z39) or 3-4 weeks after the initial
application. Propiconazole can also be used as the second
spray for improved control of other leaf diseases (e.g.
yellow spot). For early leaf rust management, an early
fungicide spray treatment can be more effective than seed
dressing or in-furrow fungicide applications.
- Fungicide applications
were more economical on high yielding crops (≥ 3 t/ha) than
lower yielding crops. Control of rust and powdery mildew was
economical in crops yielding under 2 t/ha.
- Stubble-borne,
spot-type net blotch was a major constraint to
malting grade barley production. Stubble management
experiments revealed that even two-year-old stubbles can
initiate the disease. In areas where the disease occurs
frequently, a minimum three-year rotation is recommended
where stubble retention is practised.
Background
In the southern regions of WA,
greater intensity of cropping has resulted in greater disease
impacts in crops. Most popular wheat and barley varieties are
susceptible or moderately susceptible to a range of foliar
diseases. Existing disease management provides only partial crop
protection. Opportunities for improving integrated crop disease
management involving cultural, agronomic and plant resistance
strategies were required.
This project examined the
economic use of fungicides as part of integrated disease
management, since they have been under-utilised in barley and
wheat production in the medium to high rainfall southern region
of WA. This approach became more feasible following substantial
price reductions in available off-patent fungicides.
Of the many diseases present,
spot-type net blotch, powdery mildew and leaf rust on barley and
leaf rust, stem rust and powdery mildew of wheat were studied.
Methods
Between 1998 to 2000, a series
of field experiments were undertaken to identify suitable
fungicides from the currently available experimental and
commercial products, including off-patent fungicides. Timing and
number of applications, rates and methods of application (seed
dressers, in-furrow and foliar spray) were examined.
Selected results
- Devastating outbreaks of
spot-type net blotch in barley (particularly in Franklin and
Gardiner varieties) occurred in the southern region. A
single application of commercially available products
containing propiconazole such as Tilt 250EC at 250-500mL/ha
at late stem elongation (Z39) contained the disease,
resulting in increased yields and improved grain quality (in
commercial barley crops yield increases up to 55 % were
recorded). The chemical is now registered for controlling
this disease in all Australian states. High rates of
application were more effective on high yielding crops or at
high disease pressures.
- In addition, an
experimental fungicide, BAS500F 250EC (containing the active
ingredient pyraclostrobin) was also effective in controlling
barley net blotch when used at a similar rate at Z39.
- Powdery mildew in barley
can appear at early stages or late stages of crop growth.
Fungicide experiments compared early disease control
strategies with the conventional spray later in the season.
Seed treatments with flutriafol (Armour® at 400g /ha) or
triadimenol (Baytan® at 150g/100kg seed) were effective for
up to 8 weeks. Flutriafol (Impact 250SC at 400g/ha) and
triadimefon (Accord 125EC at 800 mL /ha) applied as
in-furrow treatments with fertiliser can provide protection
for up to 16 weeks.
- Late season powdery mildew
was controlled by a single application of triadimefon (Triad
125EC), propiconazole (Tilt 250EC) or tebuconazole (Folicur
430SC) but application of Triad 125EC at 1000mL /ha was the
most cost effective. Early and late season disease
management increased yields by up to 7 to 13 per cent. Grain
quality was not affected.
- Several products
containing triadimefon (Triadimefon 125EC, Triadimefon
500WP), flutriafol (Impact 250SC) and tebuconazole (Folicur
430SC) were evaluated against barley leaf rust. Under severe
disease pressure, a single application of all the fungicides
tested at 62 gai/ha resulted in yield increases of between
30 and 42 per cent. Further work on this disease continues.
- Under moderate septoria
nodorum and septoria tritici blotch disease pressure in
wheat, foliar tebuconazole (Folicur 430SC) was up to twice
as effective at increasing yield compared to flutriafol
(Impact 250SC) or triadimefon (Triadimefon 500WP) in-furrow
fungicides. Further work on this disease is continuing.
- A single application of
triadimefon (Triad 125EC at 125 gai/ha ) protected wheat
crops from yield loss against severe leaf rust.
- When leaf rust in wheat
occurred very early (late seedling (Z25) or early stem
elongation (Z31)), a combination of early triadimefon
treatment (Triadimefon 500WP in-furrow at 100 gai/ha) and
conventionally timed triadimefon (Triad 125EC at 125 gai/ha
at Z41) achieved disease control. However, where early
infection occurred, a single foliar application during stem
elongation can be more effective than disease suppression
achieved through seed treatment or in-furrow fungicide. Two
applications of 32 gai/ha gave the same response as a single
application of a standard rate of 63 gai/ha. Yield responses
up to 34 per cent were recorded.
- Application of fungicides
Triad 125 EC (at 63 to 125 gai/ha) or Tilt 250EC (at 63 gai
/ha) at the onset of powdery mildew infection in wheat
during spring successfully controlled the disease and
increased yields by up to 17 per cent. The unregistered
fungicide, Strobilurin (AMISTAR 500WG at 125 gai /ha ) was
also very effective, increasing yields by up to 23 per cent.
- Yield losses in wheat of
12 per cent were recorded under low disease pressure from
stem rust whereas higher disease pressure decreased yield by
around 46%. Tebuconazole based fungicide (Folicur 430SC) was
most effective when applied immediately following detection
compared to a three week delay. Single fungicide
applications provided partial protection from stem rust, two
sprays being required to minimise yield loss where infection
commenced early, several weeks before head emergence.
Other information
The project has produced many
extension and conference articles.
Eureka files
(summaries of GRDC research projects) are produced by Allan
Mayfield and Jon Lamb Communications on behalf of GRDC.
Disclaimer
Any recommendations, suggestions or opinions contained in
this publications do not necessarily represent the policy or
views of the Grains Research and Development Corporation. No
person should act on the basis of the contents of this
publication without first obtaining specific, independent
professional advice. The Grains Research and Development
Corporation will not be liable for any loss, damage, cost or
expense incurred or arising by reason of any person using or
relying on the information in this publication.
Document in PDF format:
http://www.grdc.com.au/growers/res_summ/pdfs/DAW589.pdf
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