Ho Van Chien, Southern Regional Plant Protection Center, Long Dinh, Vietnam,
Nguyen Van Toan, An Giang Plant Protection Sub Department, Long Xuyen, Vietnam,
Monina Escalada, Visayas State University, Philippines, and
K.L. Heong, International Rice Research Institute, Los Baños, Philippines.
Most farmers spray their rice crops with insecticides thinking that insecticides are necessary inputs. In a recent report, FAO declared that “Most tropical rice crops under intensification require NO insecticide use” . Way and Heong (1994) argued that “rice pest management should be based on the contention that insecticides are NOT needed rather than they are and only to be used when pests are “guilty” and only as the last resort.”. However in most rice growing countries farmers are urged to apply prophylactic insecticide applications, often up to 8 times a season. Escalada et al in an earlier post addressed this question and presented data from China, Thailand and Vietnam to show that farmers who sprayed more did not have higher yields and in some cases even suffer yield decreases. Farms that had received insecticide sprays in the early crop stages were 10 times more vulnerable to crop failures caused by hopperburn.
Recently we conducted 4 farm surveys of 2106 respondents and examined the relationships between farm yields and the number of insecticides used. Using regression analyses with yield as the dependent variable and number of insecticide sprays as the independent variable we found no significant relationships in 3 of the data sets. The plots and statistics are presented below.
In Tien Giang province, farm yields were negatively related to the number of insecticide sprays applied, although they were statistically not significant. Average yields in 2010 and 2011 were 6.69 and 6.78 tons/ha, respectively. For An Giang province regression was significant in the 2011 data and the relationship was negative,
Yield = – 0.14 sprays + 7.83
In 2012 the regression was statistically not significant. Average yields were 7.34 and 7.30 tons/ha, respectively. Since it costs about US$15 to 20 per ha to apply one insecticide spray and a kilogram of paddy at farm gate is only US$0.22, in order to just make even an insecticide spray will need to gain 68 to 90 kg/ha of produce. The data sets showed that the gain per spray is negligible and even negative thus suggesting that farmers’ insecticide use tends to result in net loss rather than gain.
These farm data provide further evidence to doubt that insecticide sprays applied in rice farming contribute to increases in production or profits. Often yields and insecticide applied are negatively correlated. Farmers who did not use any insecticides had about average yields of 6.65 tons/ha in Tien Giang (n=66) and higher than average yields of 7.78 tons/ha in An Giang (n=8). This supports the contention of FAO and IRRI that “most tropical rice under intensification requires NO insecticide sprays”.