In 2005-06 rice production in Vietnam, particularly in the Mekong Delta, suffered a major setback when outbreaks of brown planthopper (BPH) caused a loss of ~400,000 tonnes (1.1% of national production). The BPH infestation threatened rice exports and also prompted farmers to spray insecticides indiscriminately and excessively in attempts to curb the spread of viral infections transmitted by BPH. This small research activity focused on helping the Ministry of Agriculture and Rural Development of Vietnam to identify research and implementation issues related to management of the BPH/virus problem. Researchers investigated the biology of the viruses, vector-virus relationships, vector migrations, vector ecology and farmers' perceptions of the vector and viral diseases, and applied the knowledge gained to develop an integrated management strategy for the BPH/virus problems.
Researchers used an analytical framework to analyse factors that caused the pest outbreaks. They determined that weather and socioeconomic factors were the main driving variables. There had been slight elevation in temperatures but these were inconsistent. The increase in abnormally strong winds might have contributed to the rapid spread, but there is need for a more thorough analysis using meteorological models and local data. Over the previous 3 years there had been an increasing trend in domestic rice prices and growing of aromatic varieties like "Jasmine". These might have influenced farmers' increasing use of insecticides, which had disrupted the biological control ecosystem services.
The increase in pest tolerance to insecticides such as fipronil and imidacloprid is another sign of high insecticide use. Using five micro-satellite markers, the scoping team found little genetic variability between pest populations in the north, central and south, which implies that planthopper populations move freely between geographic regions and could be the main cause of the rapid virus disease spread. While this pilot study provided an overview of planthopper genetic structure, the geographic coverage of sampling was insufficient to make general conclusions about the movement of BPH throughout Vietnam. Further monitoring of planthopper genetic variability using several of newly developed microsatellites will be useful in characterising planthopper movement between different geographic regions.
Leaf samples collected from southern, central, northern Vietnam and near the Vietnam border in Cambodia showed the presence of three main viruses - Rice Ragged Stunt (RRSV), Rice Grassy Stunt (RGSS) and Rice Tungro Spherical Virus (RTSV). Depending on the combination and the timing of the infections, plants exhibited a wide range of symptoms, collectively referred to as 'yellowing syndrome', from mixed infections. RRSV was detected in all areas. Near Hanoi, the leaf samples were possibly from hybrid rice which implies that the white back planthopper (WBPH) might be a new vector.
The Plant Protection Department developed an 'escape strategy' as an interim technique to prevent the spread of the planthoppers and virus diseases. This is based on observing light trap catches to synchronise seeding times in order to avoid disease transmissions and using prophylactic pesticide applications. The strategy has apparently worked. However the reliability of the light trap is a concern and the strategy also lacks scientific evaluation. There is thus need for research to evaluate and develop a more robust improvement.
Some scientists on the other hand advocated using prophylactic insecticide seed treatments to prevent disease transmission by immigrating insects. But since disease transmission period is brief, successful transmission may have occurred before the insect is killed by the insecticide. Besides, the planthoppers have developed high tolerance to the insecticides imidacloprid (>50 folds) and friponil (> 4 folds).
Interviews with farmers, extension, research and policy personnel showed that central and provincial governments distributed 2 million guidebooks, 2.5 million leaflets, >2,000 posters, 1,000 television broadcasts and organised 9,219 one-day training courses covering 404,938 farmers to combat the BPH/virus problem. With pesticide industry support, the Plant Protection Departments also organised 13 large-scale demonstration fields on the escape strategy.
The team analysed the differences in concerns and information needs of various stakeholders that had contributed to the variety of decisions in handling the crisis. Policymakers focused on ensuring food security and political stability and thus released emergency funds. Chemical industries focused on increasing sales of pesticides for the emergency. Extension sought a rapid means to contain the problem, while research needed to develop scientifically proven techniques. Farmers' main concerns were preventing loss but they lacked sufficient information. The Mekong Delta farmers, who had greater access to information through mass media than counterparts in Central Vietnam, had clearly more knowledge on pest and virus management. Thus a greater effort for communication and training of farmers in using the "escape strategy" would have greater benefits and more sustainable than distributing pesticides.
At a final workshop the research team advocated a seven-step management plan to refine and focus the efforts to deal with the planthopper/virus problem in Vietnam.
Links:
[1] http://www.aciar.gov.au/country/Vietnam
[2] http://www.aciar.gov.au/programarea/Crop Protection