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Thai farmers’ views on paraquat and integrated weed management

22 February 2019

Sugarcane: a major crop in ThailandSugarcane: a major crop in Thailand In Thailand more than 1600 farmers have participated in a survey conducted to understand how paraquat is being used in integrated weed management (IWM).

Farms growing maize, sugarcane, cassava, rubber, oil palm and fruit were selected at random from provinces in five regions across the country.

Trained representatives from universities and government agencies interviewed farmers using a questionnaire designed to gather information on their farms and cropping practices. The focus was on crop protection problems, weed management and the advantages and any disadvantages of the non-selective herbicides paraquat and glyphosate.

This first article on the survey looks at its findings and conclusions from farmers growing the field crops maize, sugarcane and cassava.1 A subsequent article will look at the orchard and plantation crops.

About the survey

Most arable land in Thailand is cropped with rice. Maize, cassava and sugarcane are the most next widely grown arable crops.

The majority of farmers interviewed were 41-60 years old (64%) with many years’ experience of farming, nearly all had received at least primary education and around three-quarters were owners of smallholdings of up to about three hectares. Others had larger farms of up to 16 ha. The areas harvested of these crops and changes over time are shown in Fig. 1.2

Figure 1. Harvested areas of maize, cassava and sugarcane in Thailand since 1990.Figure 1. Harvested areas of maize, cassava and sugarcane in Thailand since 1990. In recent years, some farmers have reduced their maize area in favour of cassava and sugarcane, but it is still a major crop with more than one million ha and yields have increased from 2.5 – 4.0 t/ha since 1990. Grown for food and animal feed, maize particularly supports the domestic poultry sector and the increasing quantity of chicken meat exported from Thailand.2,3

Cassava is a root crop, important for its starch, and Thailand has been one of the leading producers. Three-quarters of production is exported. It is a low input crop, which can be grown all year round. Yields have increased by one third over the past 30 years.2,3

Thailand ranks second in sugar exporting countries with important markets for sugar from cane as a food ingredient and as a raw material for bioethanol fuel. Good prices have driven a steady increase in the area of sugarcane and average yields have increased by 40% since 1990 to around 70 t/ha.2,3

Survey findings

Farmers growing these crops ranked weeds as posing a much more important threat to good yields than insect pests and diseases. Apart from competing with the crop for water, light and nutrients, weeds shelter rodents and interfere with harvesting. Farmers were especially concerned that weeds should not be allowed to benefit from fertilizer applied to their crops.

Traditionally, fields are plowed then left for up to two weeks for weeds to desiccate before a seedbed is prepared and crops are planted. Nowadays, non-selective herbicides are often used before plowing (Table 1.). This means better and faster weed control, which enables earlier planting and potentially higher yields and better prices. Inter-row weed control in the growing crops is also practised.

Table 1. Farmers surveyed using non-selective herbicides (%).

  Maize Cassava Sugarcane
Paraquat 40 43 55
Glyphosate 11 40   5


Pros and cons of paraquat and glyphosate

Farmers were especially impressed by the fast action and rainfastness of paraquat. They also recognised its broad-spectrum activity, its contribution to reducing soil erosion and its value for money. They noted that weeds do regrow, but this is what helps resist soil erosion. They also remarked on the pungent smell, which is an important safety feature in Syngenta paraquat products.

Farmers appreciated glyphosate’s outstanding ability to control perennial weeds, but were concerned about its slow action and poor rainfastness. Although glyphosate’s strength is its ability to control a very broad spectrum of weeds, a significant number of farmers mentioned that some weeds were not being controlled when they applied glyphosate. This is very concerning, for while only a small number of instances of weed resistance have been officially recorded in Thailand, glyphosate resistant weeds now pose a huge problem in many parts of the world.4

Scope for improvement

The survey revealed some points for improvement in the use of paraquat and integrated weed management.

First, around 98% of the farmers surveyed were plowing their fields, indicating considerable potential to promote conservation tillage, which would not only save costs (e.g. fuel), but also help to protect the soil.

Second, one third of farmers said that they used hollow cone nozzles for spraying herbicides. These nozzles are designed for the application of fungicides and insecticides. When used for spraying herbicides they generate small droplets that tend to drift and may damage crops, as well as reducing the amount of herbicide reaching the target weeds. Paraquat should be sprayed with flat fan or other recommended nozzles.


  1. Maneechote, C (2015). Integrated weed management with the use of non-selective herbicides - a position paper for Thailand agriculture. Weed Science Society of Thailand.
  2. FAOstat
  3. Food and Fertilizer Technology Centre for Asian and Pacific Region (FFTC) Agricultural Policy Platform
  4. International Survey of Herbicide Resistant Weeds