Table 4. Control of larval density of DBM (Plutella xylostella) at cabbage fields by treatment with attractant traps and/or insecticidesa).
| Trial plot | Number of DBM larvae (larvae/plant)b) | |||||||
|---|---|---|---|---|---|---|---|---|
| Treatment | Area (m2) | Duration after the start of the treatment | Increasing rate | |||||
| Test 1 | 2 weeks (A) | 4 weeks | 8 weeks (B) | (B/A) | ||||
| Six traps (120 traps/ha) | 500 | 2.5±0.6 | a | 0.8±0.3 | ab | 6.7±3.0 | b | 2.7 |
| 30 traps+two sprays of insecticides | 2500 | 1.3±0.4 | c | 0.4±0.3 | b | 5.0±2.1 | b | 3.8 |
| Six sprays of insecticidesc) | 700 | 1.6±0.3 | bc | 0.9±0.3 | ab | 7.0±2.8 | b | 4.4 |
| Control | 300 | 1.7±0.5 | ab | 1.1±0.5 | a | 13.7±3.6 | a | 8.1 |
| Test 2 | 2 weeks (A) | 4 weeks | 7 weeks (B) | |||||
| Nine traps (ca. 130 traps/ha) | 700 | 2.6±0.8 | 2.2±0.8 | a | 5.6±1.9 | ab | 2.2 | |
| Nine traps+two sprays of insecticides | 700 | 3.2±1.4 | 1.5±0.6 | ab | 7.9±2.8 | ab | 2.5 | |
| Eight sprays of insecticidesd) | 760 | 1.7±0.7 | 0.9±0.6 | b | 3.6±0.9 | b | 2.1 | |
| Control | 140 | 2.3±1.4 | 2.7±0.8 | a | 9.4±2.5 | a | 4.1 | |
a) Test 1 was carried out at Anh Dao Farm, Da Lat city, Lam Dong province from 25 February to 22 April, 2017. Test 2 was carried out at Tham Don ward, My Xuyen district, Soc Trang province from 1 January to 17 February, 2018. Cabbage seedlings were planted 2 weeks before the start of each test, and the cabbages were harvested 10 and 9 weeks after the planting in Lam Dong and Soc Trang, respectively. b) Mean±S.E. (n=5). Values within each test followed by the same letter are not significantly different at p<0.05 by Tukey–Kramer Test. c) Sprays of diazinon, cypermethrin, emamectin benzoate, or Bacillus thuringiensis during the cultivation period (about 10 weeks). d) Sprays of profenofos or emamectin benzoate during the cultivation period (about 9 weeks).