Manit Luecha and Pranee Chonun
Chainat Rice Seed Center, Rice Department, Thailand
Hopperburn in Chainat
From July 2009, Central Thailand was heavily infested by brown planthoppers (BPH) and 2 years later the problem is still continuing with hopperburn areas reported in Lop Buri, Pathumthani, Ayuthaya, Angthong, Supanburi, Phitsanulok, Phichit, Kampaengphet and Chainat. Crops were heavily infected with two viruses, the grassy stunt and ragged stunt, and many areas are still heavily infested by them. In January 2010 the government had to revise production forecasts reducing it by 1.2 million tons
or 4% (normal annual rice production around 30 million tons). In addition the government released about US$20 million supported by provincial and local governments for insecticide distribution and 1,240 million Thai baht (US$ 41 million) to compensate farmers’ losses. Many farmers had borrowed money to finance their input costs and were in debt because of consecutive crop failures due to BPH and virus diseases. Rice production in Central Thailand continues to be vulnerable to BPH attacks. Last year, Chien et al
contributed a post suggesting that in Vietnam farmers who spray their crops in the early crop stages (first 40 days after sowing) were 10 times more vulnerable to hopper attacks. In our attempts to better understand some underlining factors that promote BPH populations, we conducted a similar research and interviewed 125 farmers with various degrees of BPH attacks.
All the respondents sprayed their crops, varying from 2 to 20 sprays, with an average of 6.7 sprays per season. About 92% of the farmers applied their first insecticide sprays in the first 40 days after sowing and most common compounds were abamectin, cypermethrin and chlorpyrifos. We grouped farmers into 4 categories and found that the farms with 10 and more sprays yielded lowest. The chart below shows the negative relationship between yield and number of sprays (click here too) farmers used.
Relationship between yield per ha and number of insecticide sprays used
All the farms had some degrees of hopperburn. We asked farmers when was their first insecticide application and also to estimate their losses due to hoppers in kg/ha. We used > 100 kg loss as an indicator of heavy hopper attacks and found that 72% of the farms were heavily attacked. We cross tabulated the cases and found that 71% of the farms with early spray had heavy hopper attacks. Average yields of farmers that had sprayed in the first 40 days were 5722 kg/ha while those that had sprayed their fields later were 5948 kg/ha. The differences were not significant.