.

Date: 20 Jul 2007
Source: VietNamNet Bridge [edited]
<http://english.vietnamnet.vn/social/2007/07/720687/>

A total of 143 000 hectares (346 000 acres) of summer and winter rice crops in the Mekong Delta region are being plagued by insects. This is twice as much as the area under attack in early July [2007].

According to Viet Nam News Agency, the provinces suffering the most are Kien Giang, Bac Lieu, Tien Giang, Tra Vinh, and Hau Giang. In these areas, insect density ranges from 1000 to 2000 insects per square meter.

In some places, it is as high as 20 000 per square meter. In many provinces, 20 to 100 percent of the insects caught in insect traps carry _Rice grassy stunt virus_.

According to the Department of Plant Protection, during this rainy season, the southwestern wind is likely to spread insects to large areas throughout the Mekong Delta region, attacking summer and winter crops.

Insects have spread as far as Ho Chi Minh City, where in recent days local residents have been harassed by insects swarming around street lamps and insect corpses littering their houses.

Local experts said that every night, from 30 000 to 40 000 insects flew into lamp traps and this would continue with the number rising as high as 150 000 insects per trap per night. Farmers have been advised to start sowing one to 3 days after insects fly into the highest lamp traps.

--
Communicated by:
J. Allan Dodds
Former ProMED-mail plant disease moderator <dodds@ucr.edu>

[_Rice grassy stunt virus_ (RGSV; genus _Tenuivirus_, family _Bunyaviridae_) is transmitted by the planthopper species _Nilaparvata lugens_, _N. bakeri_, and _N. muiri_ in a persistent manner (that is, viruliferous insects remain infective for life). It is acquired by feeding by both nymphs and adults, multiplies in the vector, and is retained during moulting, but it is not passed on to the insect progeny. The virus is not transmitted by seed, pollen, or mechanical means.

Due to the specificity of the vector, rice (_Oryza sativa_) is the only natural host. Symptoms are severe stunting, excessive tillering ('grassy' appearance), erect growth habit, leaf spots, and reduced pale leaves. Infected plants usually survive until maturity, but produce no panicles. RGSV has been reported to cause serious damage in limited areas during sporadic outbreaks of its vector. It is spreading in large parts of the rice-growing areas of Asia. Disease management includes rice varieties resistant to the virus or the vector, chemical or biological vector control, and cultural practices (for example short term draining of rice fields, rice-free periods, staggered nitrogen applications).

_N. lugens_, the Asian brown planthopper, is one of the worst pests of rice in the Australasian and Pacific Island region. It causes yellowing, browning, and drying of plants and leaves small injuries exposing the plant to fungal and bacterial infections. It is also the vector of _Rice ragged stunt virus_ (RRSV; genus _Oryzavirus_, family _Reoviridae_).

A number of other rice viruses are spread by green leafhoppers (_Nephotettix_ species). The report does not specify which insect species are involved and a mixture of planthoppers, leafhoppers, and other species is likely.

Maps
Viet Nam and neighbours:
<http://www.lib.utexas.edu/maps/middle_east_and_asia/vietnam_pol01.jpg>
Viet Nam provinces:
<http://www.angelfire.com/co/hongnam/vnmap.html>

Pictures
RGSV symptoms on whole rice plants:
<http://www.knowledgebank.irri.org/RiceDoctor_MX/projectImages/image138.jpg>
RGSV symptoms on rice leaves:
<http://www.dpvweb.net/dpv/showfig.php?dpvno=320&figno=04>
Electron micrograph of _Tenuivirus_ particles:
<http://image.fs.uidaho.edu/vide/images/a9.jpg>
Brown planthopper:
<http://www.agric.nsw.gov.au/Hort/ascu/fulgor/nlugens.htm>

Links
RGSV disease information:
<http://www.knowledgebank.irri.org/RiceDoctor_MX/Fact_Sheets/Diseases/Rice_Grassy_Stunt_Virus_(RSGV).htm>
RGSV description and taxonomy:
<http://image.fs.uidaho.edu/vide/descr688.htm>
RRSV description and taxonomy:
<http://image.fs.uidaho.edu/vide/descr691.htm>
Brown planthopper information:
<http://www.knowledgebank.irri.org/RiceDoctor_MX/Fact_Sheets/Pests/Planthopper.htm#Common>
Green leafhopper information:
<http://www.knowledgebank.irri.org/RiceDoctor_MX/Fact_Sheets/Pests/Green_Leafhopper.htm>. 
- Mod.DHA]

[see also in the archive:
Virus disease, rice - Viet Nam (02) 20070614.1939 Virus disease, rice - Viet Nam 20070611.1899
2006
----
Ragged and grassy stunt, brown planthopper, rice - Viet Nam 20061103.3157]

The news item on this page is copyright by the organization where it originated - Fair use notice

Other news from this source