by
Manit Luecha, Director Chainat Seed Center
Rice Department, Thailand
A large variety of insecticides are sold for rice pest control. Farmers rely on salesmen’s recommendations when selecting what pesticide to use.
Insecticides are known to cause secondary developments and resurgences in brown planthopper (BPH) populations. They disrupt the food web structures, disorganize predator-prey relationships and favor rapid population developments of invading BPH resulting in hopperburn (Heong and Schoenly, 1998). Broad spectrum insecticides that have strong effects on natural enemies tend to make rice fields more vulnerable to hopperburn. We surveyed 341 farmers’ insecticide use in Chainat in August 2009 just prior to the massive BPH outbreaks in Central Thailand.
Farmers were growing rice varieties Phatum Thani 1 (61%), Suphan Buri 3 (14%), Chainat 1 (12%) , Suphan Buri 1 (8%), Suphan Buri 60 (3%) and 3 other varieties. On average they sprayed insecticides 3. 1 times with some as many as 12 times and some none at all. We looked at the types of insecticides that farmers used at the various crop stages (Table 1). The insecticides Abamectin (37%), Cypermethrin (12%), Chlorpyrifos (13%) were used in all crop stages although they were only recommended for treating leaf folders. These three insecticide accounted for 62% of all farmers using insecticides. In focus group discussions, we found that farmers’ insecticide selections had been based on recommendations from the pesticide salesmen. Pesticides are called “ya” which mean medicine and they are good for all insects.
Farmers often spray their crops at very early stages using mist blowers. Such practices are detrimental to aquatic and biological control fauna.
Table 1. Percent of farmers using each insecticide at different crops stages
|
Crop stages (days after sowing) |
|||||
| Insecticide |
0-15 |
16-40 |
41-60 |
61-70 |
> 70 |
|
|
|||||
| Abamectin |
39.1 |
31.0 |
40.0 |
39.1 |
37.5 |
| Cypermethrin |
26.0 |
3.3 |
20.0 | 2.2 |
6.3 |
| Chlorpyrifos |
15.6 |
8.7 |
13.3 | 10.9 |
15.0 |
| Dinotefuran |
4.2 |
14.6 |
6.7 | 10.9 |
0 |
| Fenobucarb |
0.8 |
0.3 |
6.7 | 2.2 |
0 |
| Cartap hydrochloride |
4.0 |
5.1 |
0 | 8.7 |
0 |
| Imidacloprid |
0.6 |
3.0 |
0 | 4.3 |
5.0 |
| Fipronil |
0.2 |
3.6 |
0 | 0 |
0 |
| Buprofezin |
0.8 |
3.8 |
0 | 2.2 |
0 |
| Dimethoate |
0.2 |
8.0 |
0 | 8.7 |
25.0 |
| Carbofuran |
2.5 |
2.0 |
0 | 2.2 |
5.0 |
The three most popular insecticides that Chainat farmers had used had poor ecological properties (Table 2). They have high toxicities to fish and aquatic fauna as well as bees. Toxicities to key natural enemies were not available but their high toxicities to bees would mean that they are likely to be toxic to hymenopterans, including parasitoids. Spiders tend to be susceptible to similar ecological properties and were probably badly affected as well.
Large areas in Chainat province were damaged by hopperburn
Table 2. Ecological effects – Toxicities of selected insecticides on some non target organisms
| Toxicity to | Abamectin | Cypermethrin | Chlorpyrifos |
| Birds | Non | Non | Moderate |
| Bees | High | Highly | High |
| Fish | High | Very High | Very high |
| Aquatic fauna | Extremely high | Very high | High |
Source: http://extoxnet.orst.edu/pips/
The three insecticides are known to have detrimental effects on biological control elements and cause resurgences. Their frequent usage in Chainat have probably disrupted the biological control services and increased the vulnerability of rice fields to hopperburn.
Reference
Heong, K.L. and Schoenly, K.G. 1998. Impact of insecticides on herbivore-natural enemy communities in tropical rice ecosystems. Pp 381-403 ( P. T. Haskell and P. McEwen Eds.) Ecotoxicology: Pesticides and Beneficial Organisms. Chapman and Hall, London.
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From bemused in the rice fields, Krasieow, Samchuk, Suphanburi:
It seems that there is a lot of knowledge already on how to control BPH outbreaks on this website where the contributors include several Rice Research Centre’s in Thailand so the question is why is the Rice Department (i.e the one in Bangkok) not giving out this info to the farmers in Central Thailand and conducting a campaign like the 3 Gains used in Vietnam? All the Rice Dept seem to have done is a 2 day very limited campaign (not even a sniff of it around here) and the Thai Govt , is to prevent farmers growing rice by stopping the water supply but as this website reports the BPH problems has only gotten worse in the first quarter 2010 as there are some farmers who have continued to grow rice.
There is absolutely no information at the level of the farmer here on how to prevent BPH as explained here on this website and the farmers are most probably going to do the same thing as last season, i.e. as reported in this article, to use the lots of insecticides soon after sowing.
It seems strange the author of this article i.e Director of Chainat Seed center knows the cause and solution to the BPH problem but the solution is not being put into practice by the Govt. I assume that the Rice Department also know about the information on this site as they are mentioned here too. Surely its worth giving a campaign like the 3 Gains a try but there is absolutely zilch happening here from the local or Central Govt’s.
Quite a despairing situation when it doesn’t have to be… from one of the worst if not worst affected province in Thailand.
Peter
You are right. The knowledge to manage secondary pests like planthoppers is known. These pests become problems when key ecosystem services are destroyed. Thai farmers have poor knowledge of pesticide properties and they had been sold insecticides that are resurgence causing. Although knowledge is available, the current pest control structures, attitudes and policies, created 50 years ago continue to promote pesticides as the main “control” measure. The 3 reductions 3 gains program in Vietnam had been successful because the minister of agriculture had supported it. He had allocated funds towards extending the program and it became a item in the Ministry’s budget. For Thailand to adopt such a program will require more than knowledge. It will require political support, change in attitudes and adhustments to policies in pest control. At the moment Thailand is facing political problems that are far more important than planthoppers and I think it will be difficult to expect support for a campaign that will ask farmers to stop spraying to conserve natural control. Giving out free pesticides would seem more acceptable although this will continue to worsen the problem.