by
H.V. Chien and L.Q. Cuong
Director and Deputy Director, Southern Regional Plant Protection Center, Long Dinh, Tien Giang, Vietnam and
K.L. Heong, Insect ecologist, International Rice Research Institute, Los Banos, Philippines
Farmers typically spray on top of the canopy for leaf folder control when they see small patches of damage.
Some have postulated that rice farms that control leaf folder in the early crop stages tend to be more vulnerable to planthopper attacks (http://ricehoppers.net/2009/03/24/spraying-for-leaf-folders-increases-crop-vulnerability-to-planthopper-outbreaks/). We conducted a survey of 148 farmers in 3 provinces in the Mekong Delta where severe hopperburn had been observed last season, Tieng Giang, Dong Thap and Long An. Two thirds (66.9%) of the farms had hopperburn occurring between 45 DAS to maturity and losing an average of 1225 kg/ha each. Farms with hopperburn had significantly higher insecticide sprays (4.44) and lower yields (5.45 t/ha) than those with no hopperburn (1.67 sprays and 6.45 t/ha, respectively) (Table 1).
Table 1: Comparison of farms with and without hopperburn in Tien Giang, Long An and Dong Thap in 2008/2009 season
| Farms with hopperburn
N = 99 |
Farms with no hopperburn
N = 49 |
F |
|||
| mean | CI (95%) | mean | CI (95%) | ||
| Number of insecticide sprays | 4.44 | 4.14 – 4.74 | 1.67 | 0.95 – 2.28 | 45.9** |
| Yield (t/ha) | 5.45 | 5.18 – 5.72 | 6.45 | 6.12 – 6.78 | 19.7** |
** significant at p = 0.01
The rice leaf folder – A = Adult; B = Larva; C = Leaf damages it cause. Photo credit: S. Villareal (IRRI).
Of the 148 farms, three quarters (75%) sprayed for leaf folder control and 87% of these farms had hopperburn. Among the farms that did not spray for leaf folder control only 8% had hopperburn (Table 2). A wide range of pyrethroid, organophospate, carbamates and neonicotinoid insecticides are commonly used for leaf folder control.
Table 2: Percentage of farms with and without leaf folder control that suffered
hopperburn in Tieng Giang, Long An and Dong Thap in 2008/2009 season.
| Leaf folder control | Farms with hopperburn
N = 99 |
Farms with no hopperburn
N = 49 |
||
| Number | Within row % | Number | Within row % | |
| Without | 3 | 8.1% | 34 | 91.9% |
| With | 96 | 86.5% | 15 | 13.5% |
The survey showed that farms that used insecticides to control leaf folders were about 10 times more vulnerable to hopperburn (86.5%) than those that did not (8.1%). These farms also used more insecticides and 75% of them applied their first sprays within the first 40 DAS. In the sample 25% did not receive any insecticide sprays and 8.1% of these farms had hopperburn (Table 3). Farms that received their 1st insecticide sprays in the first 40 DAS (54.7%) were most vulnerable to hopperburn as 91.4% of these farms had hopperburn. About 20% of the farms had their 1st spray after 40 DAS and 73.3% of them had hopperburn. The data provides further evidence that early insecticide sprays in the 1st 40 DAS usually for leaf folder control destroy essential ecosystem services that regulate invading planthopper adults thus increasing the risk of hopperburn in the farm. Reducing early season insecticide sprays in the first 40 DAS should thus be an important component in preventing hopperburn attacks.
Table 3: Relationship between 1st insecticide sprays and hopperburn
| % of farms | % with hopperbutn | |
| Farms with no spray | 25.0% | 8.1% |
| Farms’ 1st spray between 0 – 40 DAS | 54.7% | 91.4% |
| Farms’ 1st spray between after 41 DAS | 20.3% | 73.3% |
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