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Date: 29 May 2008
Source: Western Farm Press [edited]
<http://westernfarmpress.com/vegetables/insv-lettuce-0529/>

The last thing the California lettuce industry needs is another disease, but a new one, _Impatiens necrotic spot virus_ (INSV), turned up in Salinas Valley fields in 2007.

Steve Koike, Monterey County farm advisor, said that INSV has symptoms identical to _Tomato spotted wilt virus_ (TSWV). These include multiple, brown necrotic spots on leaves and petioles, resembling pesticide or fertilizer burn. Margins of infected leaves become wilted and yellowed, and the discoloration is often seen on new leaves near the center of the plant's growing point.

The disease, which makes heads of infected plants unmarketable, has been confirmed on iceberg, romaine, and greenleaf lettuces. It has been found in fields around Castroville, Chualar, Gonzales, Greenfield, Salinas, and Soledad. Of the 20 or so fields confirmed with INSV last year [2007], most had infection of less than 5 percent, although several showed 30 percent to 50 percent infection and significant crop loss.

"INSV," Koike explained, "is a tospovirus, and, like the more commonly known TSWV, it is vectored by thrips. Typically, INSV is known to be more of a greenhouse disease concern on flowering ornamental plants. The infection of lettuce, therefore, is an apparent departure from this pattern. The exact reasons behind the INSV outbreak on lettuce are not known. INSV is very difficult to manage, and if it gets out of hand, you notice it right away."

Koike said there has also been an increase in the incidence of TSWV on lettuce in the Salinas Valley in the last 2 to 3 years. It was identified there earlier but was not considered a significant problem. It was also found last fall [2007] in several lettuce fields near Huron by Tom Turini, Fresno County farm advisor.

Investigations of both viruses this year [2008] are proposed. Working with Turini and Bob Gilbertson, University of California, Davis plant pathologist, Koike hopes to learn the source of INSV and devise management strategies for it, as well as to monitor developments of TSWV on lettuce in various parts of the state. At the moment, UC recommendations for management are to avoid planting next to infected fields, control of thrips vectors, and crop rotation with nonsusceptible crops such as small grains.

[Byline: by Dan Bryant]

--
Communicated by:
ProMED-mail <promed@promedmail.org>

[_Tomato spotted wilt virus_ (TSWV; type species of genus _Tospovirus_) has one of the broadest host ranges among plant viruses and is one of few affecting both dicot and monocot hosts. It is regarded as one of the most economically destructive plant pathogens and has had a serious impact on many crop species worldwide causing up to 100 per cent yield loss in some instances. For more information on TSWV, see links and previous posts listed below.

_Impatiens necrotic spot virus_ (INSV) was considered a strain of TSWV but has now been classified as a separate species in the genus _Tospovirus_. It also has a wide host range and has been reported on crop and ornamental hosts, including lettuce (for example an outbreak in Italy in 1997, see EPPO data sheet with link below), as well as potato and peanut in the USA (see previous ProMED-mail posts listed below). It is widely distributed in Europe and North America and has also been identified in a few locations elsewhere.

Both INSV and TSWV are transmitted by the western flower thrips vector _Frankliniella occidentalis_. TSWV is also transmitted by other species of thrips. Disease management of tospoviruses includes vector control, use of clean planting material, control of weed hosts of virus and vectors, phytosanitary measures, and use of resistant crop cultivars. Both viruses have been placed on the quarantine alert list of the European Plant Protection Organisation (EPPO).

Maps
USA:
<http://www.mapsofworld.com/usa/usa-road-map-enlarge-view.html> and <http://healthmap.org/promed?v=40,-97.6,4>
US states:
<http://www.census.gov/geo/www/us_regdiv.pdf> and via <http://www.mapsofworld.com/usa/states/index.html>
INSV worldwide distribution (October 2007):
<http://www.eppo.org/QUARANTINE/virus/Impatiens_necrotic_spot_virus/INSV00_map.htm>
Worldwide distribution of TSWV (September 2006):
<http://www.eppo.org/QUARANTINE/virus/Tomato_spotted_wilt_virus/TSWV00_map.htm>

Pictures
INSV symptoms on impatiens:
<http://www.eppo.org/QUARANTINE/virus/Impatiens_necrotic_spot_virus/INSV00_images.htm>
TSWV on a range of hosts, picture galleries:
<http://www.eppo.org/QUARANTINE/virus/Tomato_spotted_wilt_virus/TSWV00_images.htm>
and
<http://vegetablemdonline.ppath.cornell.edu/PhotoPages/Tomatoes/Tom_SpWilt/Tom_SpWiltPhotoList.htm>
Western flower thrips:
<http://www.insectimages.org/images/768x512/4387048.jpg>

Links
INSV data sheet:
<http://www.eppo.org/QUARANTINE/virus/Impatiens_necrotic_spot_virus/INSV00_ds.pdf>
INSV and TSWV information:
<http://www.ppath.cas.psu.edu/extension/plant_disease/tswv.html>  and <http://www.umass.edu/umext/floriculture/fact_sheets/pest_management/insvtswv.html>
TSWV information:
<http://www.oznet.ksu.edu/dp_hfrr/extensn/problems/tomswv.htm>,
<http://www.ipm.ucdavis.edu/PMG/r783102211.html>,
<http://www.defra.gov.uk/planth/pestnote/tswv.htm> and <http://www.apsnet.org/online/feature/tospovirus/>
TSWV fact sheet:
<http://vegetablemdonline.ppath.cornell.edu/factsheets/Virus_SpottedWilt.htm>
INSV taxonomy:
<http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/00.011.0.05.002.htm>
TSWV taxonomy:
<http://phene.cpmc.columbia.edu/ICTVdB/11005003.htm>
Description of western flower thrips vector:
<http://www.gladescropcare.com/wfthp.html>
EPPO A2 quarantine list:
<http://www.eppo.org/QUARANTINE/listA2.htm>
- Mod.DHA]

[see also in the archive:
2007
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Tomato spotted wilt virus, tomato - USA (CA) 20070608.1872
2005
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Impatiens necrotic spot, potato - USA (NY) 20050312.0735
2004
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Tomato spotted wilt, Iris yellow spot, onion - USA (GA) 20041031.2938
2003
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Tomato spotted wilt, tomato - USA (FL & GA) 20031009.2539
2002
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Tomato spotted wilt, tomato - USA (MA): Correction 20020627.4618 Tomato spotted wilt, tomato - USA (Massachusetts) 20020626.4608 Tomato spotted wilt, tomato - USA (North Carolina) 20020622.4565 Tomato spotted wilt, tomato - (USA) Virginia 20020620.4545 2000
----
Tomato spotted wilt tospovirus, crops - USA (Georgia) 20000617.0989 Impatiens necrotic spot tospovirus, peanuts - USA 20000530.0869
1999
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Impatiens necrotic spot tospovirus - Israel 19991107.1993]

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