Are farmers’ insecticide applications related to yields?

by
M.M. Escalada, H.V. Chien, Manit Luecha,  Z.R Zhu and K.L. Heong
Visayas State University, Leyte, Philippines
Southern Regional Plant Protection Center, Long Dinh, Tien Giang, Vietnam
Chainat Rice Seed Center, Chainat, Thailand
Zhejiang University, Hangzhou, P.R. China
International Rice Research Institute, Los Baños, Philippines

Last week we posted a report on farmers’ beliefs in planthopper management and one key belief related to farmers’ insecticide use was the belief that “insecticides would increase yields”.  We plotted the two variables, farmers’ yields and insecticide sprays and found them weakly or not related (see Figure 1 below).  The R² values were < 0.02 indicating that farm yields were independent of the number of insecticide sprays applied.

Table 1 shows that for sites in China, Thailand and Cai Lay in Vietnam mean yields of farms with sprays ranging from 0 to 8 had no significant difference in yields. In Cai Be, Vietnam mean yields were significantly different with farms that had more than 7 insecticide sprays yielding significantly lower than those that had no sprays. This implied that the insecticide sprays had negative effects on yields.

Table 1: Summary of farms’ mean yields with different number of insecticide sprays.

Insecticide spray categories	China	Thailand	Vietnam
	Lingui	Chainat	Cai Lay	Cai Be
Zero	-	5.31	-	5.85
1 to 2	5.50	5.32	5.32	5.25
3 to 4	5.53	5.05	5.21	5.04
5 to 6	5.71	4.72	5.14	5.04
7 to 8	-	-	6.00	4.47
More than 8	-	-	-	4.89
Between groups  F value	0.73		1.51	4.58
Probability	0.48ns	0.31ns	0.2ns	0.001**

Several economists have shown that in most cases farmers’ profits declined with increase in insecticide use (eg. Herdt, et al 1984; Waibel, 1986; Rola and Pingali, 1993). And when the indirect costs, such as those related to health, environmental pollution and ecological disruptions that increase the farms’ vulnerability to planthopper attacks are considered, farmers would be much better off not using insecticides. For instance in the Mekong Delta, farmers who sprayed their crops in the early stages, were 10 times more vulnerable to hopperburn than those who did not use any insecticides.  The inadequate and underfinanced extension services seriously hamper farmers’ selection of insecticides and equipment used by farmers. In addition the pesticide marketplaces in Asia are littered with thousands of pesticides names, packaging and mixtures making pesticide selection more difficult.  In one country an active ingredient is sold in > 1000 trade names. We found a trade name “Big and small, kill all” sold without any content information in the label. Most farmers often mix three or four insecticides into one spray hoping to widen the sprays’ kill range. Because they depend on trade names, many often ended mixing insecticides with the same active ingredients. Most farmers in Thailand, China and Vietnam depend only on pesticide retailers for insecticide recommendations and often end up using insecticides that were either ineffective or would cause planthopper outbreaks.

Pesticide sprayers in many developing countries are notoriously inadequate and poorly manufactured.  Most of them are made locally and do not meet acceptable safety and efficiency standards.  They often have poor nozzles with poor spray droplet distributions and thus most sprays droplets simply roll off the leaves and end up in the water.  Very low amounts of the sprays would reach the target pests in the rice tillers (stem borers) or at the bases of the rice crop (planthoppers). Instead natural enemies that are aquatic, highly mobile, small in size and highly susceptible usually ended up as casualties.  Indeed when insecticides are reduced marked increases in the biodiversity of predators, parasitoids and the aquatic fauna return to the rice ecosystems (Heong et al 2007).

In an earlier study done in China in 1996, farm yields were found not related to the insecticide expenditures in the 1^st season and negatively related in the 2^nd season.  This is further evidence that farmers’ insecticide sprays are not related to yields, but farmers continue to adhere to the belief that “insecticides would increase yields” which is probably the prime factor driving farmers’ insecticide inputs. This belief is strengthened by continuous repetitions in advertising campaigns that instill a “state of fear” (Crichton 2004).

References

Crichton, M. 2004. “State of Fear”.  Harper Collins Publishers, NY.

Heong, K. L. , Manza,A., Catindig, J., Villareal, S. and Jacobsen, T. 2007. Changes in pesticide use and arthropod biodiversity in the IRRI research farm. Outlooks in Pest Management. October 2007.

Herdt, R.W, Castillo, L. and Jayasuriya, S. 1984. The economics of insect control in the Philippines. In IRRI, Judicious and Efficient Use of Insecticides. International Rice Research Institute, Los Baños, Philippines.

Rola, A.C. and Pingali, P.L. 1993. Pesticides, rice productivity and farmers’ health – an economic assessment. International Rice research Institute, Los Baños, Philippines.

Waibel, H. 1986. The economics of integrated pest control in irrigated rice: a case study from the Philippines. Crop Protection Monographs, Berlin: Springer-Verlag.

Tagged as: insecticide application and yield