Home' Grower : Dec 2010-Jan 2011 Contents The South Australian Grower -- December 2010/January 2011
Pests & diseases
Trials aid sustainable disease
management in cucurbit crops
TRIALS this season have
delayed and suppressed
powder y mildew infec-
tion in cucurbit crops with
fewer fungicide applications,
using new fungicide technol-
Cucurbits are an impor-
tant family of Australian
horticultural crops, includ-
ing pumpkins, zucchini,
squash, watermelons, rock-
melons, honeydew melons
The Australia-wide cucur-
bit growing area is estimat-
ed to be 22,000 hectares
annually, and increasing,
with the southern season
currently under way.
Powdery mildew is one of
the most important eco-
nomic diseases in Australia's
cucurbit crops, and is con-
sidered high-risk for devel-
oping fungicide resistance,
with growers urgently
requiring a new approach to
ment in cucurbit crops is an
important goal of research
being undertaken at Ayr
Research Station in Australia's
Burdekin cropping region.
This season, collaborative
Queensland Department of
Employment and Economic
Development, and Crop
Care, provide good news for
southern growers in their
current growing season.
DEEDI plant pathologist
Dr Gerry MacManus has
been managing zucchini tri-
als with two new types of
fungicide being introduced
to Australia by Crop Care.
"Preliminary results from
Colliss and Vivando, on their
own or in combination,
showed promise in delaying
and suppressing powder y
mildew, compared with the
equivalent number of sprays
of sulphur," Dr MacManus
"This was evidenced by less
infection on leaves and no infec-
tion on stems -- compared with
untreated plants and plants
treated with sulphur, where
symptoms were very prominent.
"There were no obvious signs
of phytotoxic reactions to the
new fungicides on either the
foliage or fruits, and general
growth habit of plants was not
Dr MacManus said that
despite these developments,
many aspects of disease man-
agement come down to the
responsibility of the grower,
and following the label direc-
tions on the new products is
"Coliss needs to be applied as a
protectant spray before the dis-
ease becomes established -- and
prior to flowering because of
withholding period restrictions --
with no more than two sprays
per crop," Dr MacManus said.
"Regular crop monitoring is
important, so that growers
know when best to apply these
fungicides strategically for
Particular emphasis on
spray application technol-
ogy is also a must."
Crop Care has already
released Colliss onto the
market this season, and
expects Vivando to be
available to growers early
in the new year.
Crop Care national horti-
culture business manager
Kerrie Mackay said the reg-
istrations of the new fungi-
cides represented a major
opportunity for growers to
deal with powdery mildew.
However, she said it was
important that growers
and their advisers under-
stood the way the fungi-
"Colliss contains two
fungicides from different
chemical groups -- a new
strategy to delay the onset
of resistant disease
strains," Ms Mackay said.
"Vivando consists of
metrafenone -- from a new
fungicide group, never
used before on cucurbits.
It works by stopping the
fungus from entering the
leaf and causing damage,
but does not kill the initial
stages of the disease."
Ms Mackay assures that
Crop Care would provide
clear instructions on the
use of these fungicides,
including options for rota-
tion, as well as instructions
to preser ve the use of this
AYR Research Station plant pathologist Gerry
MacManus inspecting the impact of powdery mildew in
a zucchini crop, and the effectiveness of a variety of
Familiarising themselves with the best use of new powdery
mildew fungicides are Romano Parisotto and Richard Statham,
Landmark; Otto Kath, Rapisarda; and Brent Wilson, Landmark.
Mallee onion stunt cause identified
By ANGELA LUSH
OVER the past few years, onion growers in
South Australia have increasingly noticed
stunted patches within their pivots, a major
concern since more than a third of all the
onions in Australia (more than 95,000
tonnes) are produced in SA. A research
team at the South Australian Research and
Development Institute led by Dr Trevor
Wicks has been investigating the cause.
"Yield can be up to 50 per cent less in
areas with stunted plants and all red, brown
and white onions can be affected," Dr
Most of the onion production in South
Australia is undertaken in the Mallee region.
Patches of stunted onion plants are now
common within other wise healthy crops in
Stunting in onions develops as circular to
irregular patches that can vary in size from
1 metre to 25m in diameter.
Significant yield loss is occurring as the
onion growth in the stunted patches
remains retarded throughout the season.
"Stunted onions are most obvious 6-12
weeks after a late winter sowing. At this
time, diseased plants can be 50pc or less the
size of healthy plants," Dr Wicks said.
"Our research has shown that onion stunt
in the Mallee is caused by the soil fungus
The strain that causes most of the Mallee
onion stunt is known as AG 8. This strain of
the soil fungus is also responsible for a sim-
ilar condition in cereals known as bare
patch," he said.
Mallee onion stunt (MOS) may now be
becoming more widespread as onion grow-
ers regularly use cereal crops in rotation.
Using cereal crops that are also susceptible
to the AG 8 strain of Rhizoctonia could help
to sustain the fungal populations between
Rhizoctonia mycelium, the thread-like
growing structure of fungi, constricts the
This causes root rot at the crown of the
plant. Stunted plants never recover and fail
to reach full size and yield.
During the SARDI study, stunted onion
seedlings were often found with only a few
rotting roots and a well developed root sys-
This means that there may be additional
factors inhibiting plant growth.
"Some strains of Rhizoctonia solani can
produce toxins that inhibit root growth and
this could be the case in our onion crops,"
Dr Wicks said.
"Now that we know the cause of Mallee
onion stunt, we can focus on developing
control strategies for onion growers.
We are currently testing a range of soil
fumigants, drenches and spray applications
for their effectiveness against this soil fun-
The SARDI team is also developing a pre-
dictive test for disease incidence.
This could be used before the start of the
season to help growers plan their pivots and
target fungal treatments.
Details: Dr Trevor Wicks Ph: 08 8303 9563,
Cucurbit fungicides trial
Success against powdery
New products released
AT A GLANCE
PO Box 1784
Orroroo, SA 5431
ABN: 85 103 271 432
Phone: (08) 8659 0000
Fax: (08) 8659 0021
Brenton: 0428 810 088
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