Ho Van Chien, Southern Regional Plant Protection Center, Long Dinh, Tien Giang, Vietnam,
Nguyen Huu Huan, Plant Protection Department, Ho Chi Minh City, Vietnam, and
Le Quoc Cuong, Southern Regional Plant Protection Center, Long Dinh, Tien Giang, Vietnam
Brown planthopper (BPH) outbreaks are frequently followed by widespread infections of two virus diseases, grassy stunt and ragged stunt, like in Thailand. In the Mekong, BPH outbreaks in 2006 was followed by virus infections that caused a loss of about a million tons of paddy. In mid 2007 the Vietnamese government banned rice exports to conserve rice for domestic needs. The Plant Protection Department initiated an innovative large scale approach in order to contain BPH and virus damages called the “Escape Strategy” or “Chien Luoc Ne Ray” in Vietnamese. The concepts underlining this approach were the light trap trends from many years of light trap data and that most virus infection result from migrating hoppers. Thus, if crops were sown after the migration peaks, the chances of virus infections can be markedly reduced and BPH populations can also be reduced if farmers were practicing “Three Reductions, Three Gains”. This practice includes “no early spray” in the first 40 days. Rice cropping can also be synchronized thus further reducing available host sources for BPH reproduction since BPH is monophagous and can not survive in any other plant.
The virus diseases have long incubation periods in the plant as well as in the insect. In the insect, the viruses are not affected by molting. Most new infections and disease spread are likely to be carried out by new immigrants into crops. Thus when immigrants from a diseased field arrive in a fresh crop high transmission will be expected. The “Escape Strategy” is thus designed to delay sowing till after the BPH peaks have occurred to escape the peak of the migrations. In order to be effective such sowing synchrony has to be done by the whole farming communities. The Plant Protection Department (PPD) organized farming communities to conduct light traps, record the counts, plot the observations and make community decisions when to implement sowing. BPH migrating into unsprayed fields with no rice face both starvation and high mortality from predators like frogs and microvellids.
The initial results were very encouraging. The virus infected areas declined significantly. Since in many communities the BPH light trap trends were rather similar, there were opportunities to upscale so as to extend the reach. PPD conducted mass media campaigns using radio, TV and leaflets from 2007 to upscale the “Escape Strategy” and today it is believed that this strategy is practiced in more than 50% of the rice areas in the Mekong.
In March 2012, the Ministry of Agriculture and Rural Development (MARD) announced that their efforts to contain BPH and the virus spreads have been highly successful. Between 2002 and 2012 the high light trap catches from Long Dinh station were recorded in the years 2007 to 2010 and high virus infestation occurred between 2006 and 2008. In years 2009 and 2010, although BPH light trap recorded were high, areas infested by virus were relative low. From 2011 both BPH and area infested by virus had been low and no field was destroyed by virus diseases.
Besides the “Escape Strategy” the successful containment of BPH and virus infestations in the Mekong was also due the government’s efforts to reduce insecticide misuse through “Three Reductions, Three Gains” implementation. Recent farm surveys showed that about 50 to 60% of the farmers did not apply insecticides in the first 40 days, one of the three reductions. Farmers’ insecticide sprays had remained below two sprays per season in Tien Giang. The government is also increasing efforts to curb insecticide misuse and had recently developed Circular # 18 to regulate distribution and marketing of pesticides. With increasing popularity and scaling up of applying ecological engineering, rice fields in the Mekong will continue to have higher biodiversity and resilience and reduce vulnerability to hopper outbreaks. Thailand is expected to implement a similar approach in the Central Plains to reduce BPH and virus disease outbreaks.