VA-MarApr2017lr

18-19 / 56

18 | March/April - 2017 | 19
R&D | BROWN ETCH |
Brown etch, or Rust mark, is a major problem for many Australian pumpkin growers, especially producers of
butternut varieties. It regularly results in significant losses on-farm, product quality downgrades or rejections in
the market. Dr Jenny Ekman from Applied Horticultural Research (AHR) explains the damage Brown etch can
cause to pumpkins and the factors behind it.
ATTENTION PUMPKIN GROWERS: HAVE YOU
SEEN THIS ETCH ?
In growing regions such as Mareeba, Bundaberg and Gatton in
Queensland, pumpkin losses due to Brown etch can reach 50 per
cent or more. Sometimes, crops may be abandoned as they are not
worth harvesting, due to the large percentage of affected fruit.
Brown etch can develop in the field, where it can appear as
concentric brown rings or patterns. As the pumpkin ages, the
brown area dries and cracks, which allows for the growth of fungal
diseases and rots.
Worse, in many ways, is when the condition develops during
transport. By this time, the pumpkins have been picked,
packed and possibly trucked for thousands of kilometers, only
for them to have to be re-graded or even rejected upon arrival
at the market.
A project on this issue, entitled Improved management of pumpkin
brown etch, has been funded by Horticulture Innovation Australia
using the research and development National Vegetable Levy and
funds from the Australian Government. Led by Applied Horticultural
Research (AHR), the aim is to find out what causes Brown etch and
how to manage it.
A GLOBAL ISSUE
According to project leader Dr Gordon Rogers, Brown etch is not
just a problem for Australian growers.
3 ENDEAVOUR ST, WARRAGUL. VIC 3820
PH (03) 5623 1362
Custom made machines available
Prices on application
Any growers who have observations to contribute or would like to be involved
in the project can contact Dr Jenny Ekman on 0407 384 285 or at jenny.
.
This project has been funded by Horticulture Innovation Australia Limited
using the research and development National Vegetable Levy and funds from
the Australian Government.
Project Number: VG15064
INFO
R&D
“Brown etch occurs in any area that grows butternut pumpkins and
their hybrids. You would think that there would be lots of research
on this issue. However, there are only a handful of references, and
surprisingly little is known about what causes it,” Dr Rogers said.
It is not even clear whether Brown etch is caused by a disease
or if it is actually a physiological disorder. Attempts to induce the
symptoms have had mixed results.
Vegetable pathologist Dr Len Tesoriero from the New South
Wales Department of Primary Industries (NSW DPI) has been trying
to find a causal organism on pumpkins affected by Brown etch.
“It has always been assumed that a fungus was to blame. In
the past, researchers have isolated various species of Fusarium,
while others have suggested that a type of gummy stem blight
(Didymella bryoniae) was the cause,” Dr Tesoriero said.
“However, none of these organisms can be consistently
isolated from the affected tissue. Many of the samples we have
worked on have yielded no live pathogens at all. It’s possible
this is because the fungus has already died by the time we see
symptoms. Alternatively, it may not be a fungal disease at all.”
GROWER DISCUSSION
In November 2016, the project team met with pumpkin
growers from around Australia in Mareeba, Queensland to
discuss when and where they had seen Brown etch.
According to Dr Jenny Ekman from AHR, humidity and
prolonged wetness definitely appear to be important factors.
“Crops grown on plastic mulch or sandy sites seem less likely
to get Brown etch than those grown on heavy soil, especially if
overhead irrigation is used. Growers have also suggested that it
is worse if there is a change in the weather, such as when a cold
front comes through after a long dry spell,” she said.
A series of weather stations are now being installed on farms
to examine the climatic conditions associated with the onset of
Brown etch. It is also planned to conduct post-harvest trials to
examine whether different storage and packing methods can
control Brown etch during transport.
“Pumpkins are normally packed into cardboard bins for
transport, but these have no ventilation,” Dr Ekman explained.
“Warm temperatures, high humidity and condensation inside
the bins could be making Brown etch worse during transport.
We are going to test different handling strategies, including
Chep’s new plastic, foldable bins, to try to reduce the problem.”
The research team would like to hear from growers who have
seen Brown etch in the past, or who are currently experiencing
this issue in their crops. They are also particularly keen to
analyse any immature pumpkins that are just starting to show
symptoms of Brown etch.
L-R: Pumpkin grower John Marin helps Adam Harber from AHR install
some data loggers, watched by Jim Kappas from Fresh Produce Group. Symptoms of Brown etch in a butternut pumkin.