by
Somsak Thongdeethae, Director, Chainat Rice Research Center, Rice Department, Thailand and K.L. Heong, Insect Ecologist, International Rice Research Institute, Los Baños, Philippines
Hopperburn (in red squares) in Central Thailand, August 2009
Thailand’s central plains produce about 30% of Thailand’s total rice. Rice is grown intensively in most of the irrigated areas here. Farmers either grow 3 crops a year or 5 crops in 2 years. Varietal diversity is small with farmers planting 2 main varieties, Pathum Tani 1 and Chainat 1. Inputs are generally high with farmers using > 200 kg seed rates, > 200 kg nitrogen and between 3 to 6 insecticide sprays. Crop establishment methods are direct broadcasting and machine transplanting and pesticides are applied using knapsacks, mist blowers or tube dusting. Most farmers adopt prophylactic insecticide applications of imidacloprid, buprofezin, MIPC and BPMC.
Heavy hopperburn in Sam Chuk district
In the months of June and July this year, the Department of Agricultural Extension has recorded > 100,000 rai (or 7,000 ha) are infested with high populations and 2,000 rai (or 135 ha) totally destroyed in the Suphan Buri, Ang Thong and Chainat provinces. Most of the hopper burn areas are found in districts of Sam Chuk, Don Chedi and Si Prachan, where intensive cultivation is practiced. Crops are harvested by combine harvesters and the straw is burnt immediately and the land prepared for the next crop planted within a turn around of < 10 days. Although the crop loss (~ 1000 tons) is relatively small but the intensively cultivated rice in Central Thailand remains vulnerable to planthopper invaders, especially since the rice price is high and farmers are shortening crop turnaround promoting staggered planting and increasing chemical inputs.
Rice in the central plains is grown among a rich diversity of flora, which include crops bananas, maize and fruits, and non crops like Bracharia, a perennial habitat rich in predatory crickets such as Anaxipha longipennis.
Rice fields in Suphan Buri are grown among a rich diversity of crops and non crops which serve as important refuge for predators like crickets.
The use of pesticides remains the main and often the only pest management tactic of farmers and plant protection advisors. Farmers often mix several active ingredients to broaden the spray effects and extension giving out free pesticides to farmers. Since planthopper outbreaks are insecticide induced, these practices are counter productive as they can further destroy ecosystem services. The Chainat Rice Research Center has initiated the use of ecological engineering in their experimental farm to increase floral biodiversity and enhance biocontrol ecosystem services. Combined with reduced insecticide application and use of planthopper tolerant varieties, rice ecosystems can have better crop health to resist invading hoppers.
Nectar producing flowers (e.g. Tridax sp) can serve as food resource for natural enemies, like parasitoids.
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In Yunnan about 99% of the planthopper were WBPH. Early immigrants were observed in March and the light trap in Jinping and Jiangcheng counties were 92400 (on May 6) and 65368 (on April 16),respectively totaling 0.1-0.2 millions, which was about 20 times higher than that in 2007. The infested areas included 56 counties in the south, middle and eastern parts of Yunnan (close to Vietnam, Laos and Thailand). Total areas with high WBPHdensities TL were about 6 millions Mu (~ 400,000 ha) and the insecticide control areas were more than 10 millonsMu. J Cheng, ZU
Looking at the blog and seeing the picture of hopperburn in Thailand reminded of my first visit to IRRI in the 1970s and seeing similar scenes of hopperburn due to using too many pesticides applied incredibly badly [at very high volumes - more like irrigation!] and multiple cropping so hoppers hardly needed to move to enter a fresh crop. Seemingly there is still no suitable economic crop to integrate with rice to break the cycle. If that could be achieved then perhaps there would be less need for farmers to even consider the need to spray especially if they had varieties tolerant/resistant to planthoppers. As for the application of pesticides, very little research has been done to improve the situation so it continues to be done badly with often broad spectrum insecticides.
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