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2018-04-04T14:00:00.0000000Z
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STEMPHYLIUM BLIGHT, ONION - NEW ZEALAND

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Date: Thu 29 Mar 2018 6:30 PM NZST
Source: Radio New Zealand [edited]
<https://www.radionz.co.nz/ news/country/353699/onion- crop-slashed-by-disease>

The country's onion crop has been slashed by at least 20 per cent
because of humid weather which resulted in a disease. Onions New
Zealand's Michael Ahern said the main problem was a leaf blight called
'Stemphylium' which has damaged the plants.

"We've had some difficulties in a number of the growing areas. We ran
a crop forecast recently and we could be down by around 20 per cent on
yield, even that could be increased by quality issues at packing time.
No one can recall an attack by this particular fungus to this extent.
So that does point potentially to, not a new pathogen, but more
changing climate conditions."

The industry would pour its resources and expertise into finding
solutions, he said.

[Byline: Alexa Cook]
--
Communicated by:
ProMED-mail
<promed@promedmail.org>

[Leaf blight and stem rot of onion is caused by the fungus
_Stemphylium vesicarium_. It is a serious disease of the crop that can
lead to yield losses and severe damage to seed crops. Symptoms include
water soaked lesions on leaves with yellow streaks extending along the
leaf blade; leaves may become completely blighted; coalescing lesions
may girdle and kill leaves and seed stems. Bulbs are not normally
affected, but yield losses are due to weakening of the plants.
Symptoms are similar to and may be confused with purple blotch (caused
by _Alternaria porri_). Disease development is favoured by warm, humid
conditions and extended periods of leaf wetness (as mentioned above).
The pathogen can also affect a number of other hosts, including crops
like tomato, asparagus, soybean and even trees like pear and mango,
but symptoms vary on different hosts.

The fungus survives between crops in plant debris or soil. It is
spread with contaminated plant and soil material, water, and by
mechanical means. Disease management is difficult and mostly relies on
cultural methods, phytosanitation (removal of crop debris and
reservoir hosts), and fungicides.

Other species in the genus are associated with blights or rotting
diseases in a range of crops, such as leaf spot on sugar beet and
apple core rot.

In the story above, it is not clear why the possibility of an emerging
new pathogen strain is being dismissed and why environmental changes
are considered more likely as reason for the outbreak. In any case,
one scenario would not exclude the other. It would appear that further
research on the pathogen strain as well as other factors leading to
the problems is advisable.

Maps
New Zealand:
<http://www.backpack- newzealand.com/images/new- zealand-map.gif> and
<http://healthmap.org/promed/ p/164>

Pictures
Stemphylium leaf blight on onion:
<https://onvegetables.files. wordpress..com/2012/07/fig1_ slg-e1341539192196.gif?w=500& h=247>,
<http://www.apsnet.org/ edcenter/K-12/NewsViews/ Article%20Images/stemphylium.. jpg>,
<http://vikaspedia.in/ agriculture/crop-production/ integrated-pest-managment/ipm- for-vegetables/ipm-strategies- for-onion/leafblightimg.jpg>,
and via
<http://www.invasive.org/ browse/subimages.cfm?sub=17885 > (photo
gallery)
_S. vesicarium_ conidia (microscopy):
<http://media.padil.gov.au/ species/143077/51297-large.jpg >

Links
Additional news story:
<http://www.freshplaza.com/ article/192001/New-Zealand- onion-crop-affected-by-disease >
Information on stemphylium blight:
<http://www.plantwise.org/ KnowledgeBank/Datasheet.aspx? dsid=42014>,
<http://aggie-horticulture. tamu.edu/extension/ newsletters/vpmnews/may01/ art5may.html>,
<http://www.apsnet.org/ publications/phytopathology/ backissues/Documents/ 1989Articles/Phyto79n03_301. PDF>,
via
<http://nhb.gov.in/bulletin_ files/vegetable/onion/oni002. pdf>,
<http://vikaspedia.in/ agriculture/crop-production/ integrated-pest-managment/ipm- for-vegetables/ipm-strategies- for-onion/diseases-and- symptoms>,
and
<http://www.actahort.org/ members/showpdf?booknrarnr= 358_43>
Description of _S. vesicarium_:
<http://www.padil.gov.au/maf- border/pest/main/143077/51298>
_S. vesicarium_ taxonomy:
<http://www.indexfungorum.org/ names/NamesRecord.asp? RecordID=339660>
- Mod.DHA]

[See Also:
Core rot, apple - India: (HP)
http://promedmail.org/post/ 20180329.5717077
2016
----
Stemphylium blight, onion - Kenya: (KB)
http://promedmail.org/post/ 20160104.3910614
2014
----
Stemphylium leaf spot, sugar beet - UK: 1st rep (England)
http://promedmail.org/post/ 20141015.2864444
2009
----
Fungal blight, onion - India: (MH)
http://promedmail.org/post/ 20090103.0024
2005
----
Apple core rot - India (Himachal Pradesh)
http://promedmail.org/post/ 20050808.2313]
............................... ....................sb/dha/mj/ dk
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ProMED
New_Zealand
Stemphyium
Blight
Onion

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