Need for strengthening weed control practices

National food production drive:

By Dr. L. Amarasinghe, Former senior weed Scientist and a Director, Department of Agriculture.-

October 22, 2017, 9:31 pm 

The overall productivity of both the arable and plantation crop sectors has been seriously affected by the recent droughts experienced across the whole country, reported to be the worst overthe last 40 years. This has left large extents of paddy lands, both irrigated and rain-fed, as well as other annual crops of the country, under extended fallow periods, affecting a substantial decrease in the national food productivityof the country compelling the government to import rice and other basic food items such as onions, maize etc. to fulfil the national needs. Productivity in the plantation sector has also been seriously affected.

Consequences of recent droughts in the country

According to a recent article published in a daily newspaper it is quite disheartening to note the results of a recent survey conducted by the Sri Lankan UN office indicating that over 300,000 families in drought affected areas are only fed a single meal per day while the National Disaster Management Center has declared that close to 1,989,572 people in 17 districts are seriously affected by extreme drought conditions.

In this context, President Maithripala Sirisena has rightly advised all government departments to give the highest priority to a national food production programme. The President has further declared that all cultivable land in the country should be brought under cultivation under the national food production programme. Thus, it is the responsibility of all concerned to make the proposed national agricultural production programme success.

We hope the following discussion would help realise the importance of basic land preparation prior to planting of crops to increase the overall productivity in plantation and agriculture.

The arable food crop sector

The preliminary obstacle faced by the arable crop farmers is the establishment of annual crops in lands that have been under extensive weed growth due long fallow periods experienced over several seasons. As we all know, a seed bed free of weeds is a compulsory pre-requisite for the successful establishment of any crop. Usually, this is achieved through land preparation either using animal or mechanical power. Water is adopted as a supplementary factor along with tillage in lowland rice cultivation. The duration to complete the whole process is determined largely by many factors among which initial standing weed biomass becomes a crucial one.

Over the last several decades, farmers have resorted to effective herbicide use to expedite weed killing, facilitating land preparation. In fact, 60 to 80 percent of rice farmers in major rice growing areas have adopted recommended herbicides in the past. There were then only two herbicides recommended to kill weeds prior to initiation of tillage during land preparation. However, this practice has come to an abrupt halt recently after the only two herbicides widely used by farmers, Paraquat and Glyphosate, were banned without providing suitable alternatives. As a result farmers have to resort to increased tillage practices, excessive use of water and labour to control weeds established during fallow periods.

Despite the ban, heavy illicit inflow of Glyphosate is reaching the country and unscrupulous parties/traders are involved in selling such glyphosate at highly exorbitant prizes, usually three to four times the usual prize, exploiting the poor farmers. The farmers are compelled to buy this glyphosate because of excessive labour costs for weeding. This situation applies particularly to tea estates in the plantation sector as well.

The plantation crop sector

Weed management on tea plantations is a critically important operation, particularly, during early establishment and post pruning phases. Weeds on tea estates range from soft annual dicotyledonous weeds to perennial grasses which are highly competitive. The most common method of removing weeds in the past, prior to 1960s, had been scraping. Scraping breaks down the soil structure leaving a loose layer of top soil which is readily washed away by rains. The loss of soil nutrients is considerable. The use of herbicides has substantially reduced soil erosion. It has been observed that chemical weed control is superior to manual weed control with respect to changes in some soil physical and chemical properties such as total pore space, percent aggregation, water retention total availability of water, texture, organic carbon, CEC and the percentage of total nitrogen in the long run. Further no adverse effect on micro- organisms and earthworm population has been observed with application of paraquat, in contrast to the application of systemic herbicides.

It has been reported that bimonthly application of paraquat at 0.125lb/ac is quite effective on controlling young emerging broad leaves, grasses and sedges in tea plantations. However, repeated application becomes necessary to suppress the regenerating grasses having underground propagules such as rhizomes and tubers. There is no danger of paraquat being available for root absorption at the above levels of application. No difference was recorded in yields between two monthly manual and paraquat weeding. Thus, large tea plantations heavily dependended on this chemical to control weeds due to labour shortages for manual weeding.

Despite the wide scale adoption of the two leading herbicides, Paraquat and Glyposate, over decades on tea plantations, recent steps taken to ban the two herbicides without providing alternatives dealt a serious blow on chemical weed control. Glyphosate was legally banned in 2015 on the premise that it had a role in the chronic kidney disease of uncertain aetiology (CKDu) reported from agricultural areas in North Central Province, but there has been no acceptable scientific evidence to establish it.

It has not been banned in any other country having CKDuor , for that matter, anywhere else in the world. Parquet has been banned legally in 2014 due to the risk intentional poisoning from voluntary intake.

The serious problems faced by farmers on total weed control in agricultural and plantation sectorsafter banning of these two herbicides have been seriously highlighted invarious technical forums, by university academics and other scientistsand even severalministers at the parliament. But all these efforts have been in vain. With the current labour shortage and extensive weed growth in fallow lands, mere mechanical tillage or manual labour- intensive methods becomes relatively inefficient to accomplish the expected level of initial weed control during land preparation in agricultural lands or weeding in tea plantations, unless an effective herbicide is used.

Backed by the long term experience after working with Paraquat and considering factors that led to banning of the two herbicides, Paraquat and Glyphosate, we strongly propose that Paraquat is the most proven herbicide with minimum hazards on the environment and the applicator as well. However, farmers should be educated on its safe use.

Paraquat herbicide and Regulatory status

Paraquat is a relatively non-selective, foliage-applied contact herbicide. Soils of various types are capable of adsorbing vast quantities of paraquat. Clay content is important, but even for lighter soils the adsorption capacity in the top few centimeters is capable of deactivating many kilograms of paraquat per hectare.

It is inactivated on contact with almost all naturally occurring soils and as a result no biologically active residues remain in the soil, thus allowing planting or sowing to be carried out almost immediately after spraying.

No leaching or run-off drainage to ground water.

When used as recommended, paraquat is not hazardous to fish or invertebrates because it cannot leach into water. Extensive ecological studies have shown that paraquat is not a risk to aquatic environments.

Like other pesticides, paraquat concentrate can be fatal if swallowed in sufficient quantities. Utmost care should always be taken to avoid ingesting pesticides. Minor exposure is possible from contaminated fingers or gloves, or sprays drift, but in negligible amounts and this exposure would not be expected to cause harm in any normal practice.

United Nations Environment Programme (UNEP) and the Food and Agriculture Organization (FAO) have adopted an international treaty in 1998 called Rotterdam Convention on the Prior informed consent Procedure for Hazardous Chemicals and Pesticides in International Trade, for managingchemicals that pose serious risks to human health and environment through banning or imposing severe restrictions.

The Chemical Review Committee (CRC) of the Rotterdam Convention has reviewed the notifications made by several countries against Paraquat to include in the list of chemicals subject to the Prior Informed Consent procedure (PIC). The Committee declared that the notifications did not meet the specified requirements to include Paraquat in PIC list.

Because of unintentional poisonings and absence of an antidote, Paraquat has been banned or restricted in a number of countries. The U.S. Environmental Protection Agency (EPA) allows its purchase and use solely by certified applicators. More than 100 crops worldwide are sprayed with paraquat, including in the U.S.

In developing countries, where health hazards of pesticides are pronounced, paraquat is minimally restricted. In Indonesia, its use is restricted to large estates and certified applicators. Paraquat is recommended to use over a number of crops including, rice, maize, potato, tea and cotton in India.

Immediate interventions

Immediately lift the ban on paraquat and make all necessary actions to import adequate amounts of the herbicide. Extend all assistance to the pesticide industry to expedite the importation of the herbicide and the necessary product stewardship.

Benefits and Beneficiaries

All farming community in the country who are involved in agriculture and plantation sector would be greatly benefited even through a temporary lifting of the ban imposed on Parqauat for a limited number of growing seasons at this national crisis situation

1. Over 1.0 million resource poor rice farmers in the Island, both in the dry and wet zones

who are confronted with excessive weed growth in their fallow paddy fields in current situation.

2. Land preparation in more than 40-50% of paddy lands in the wet and intermediate zones covering Matara, Galle, Ratnapura, Hambantota, Kalurtara, Gampaha, Kegalla and Kurunegala districts would be facilitated.

3. Thousands of small- scale sugarcane farmers engaged in contractual growing of

sugarcane and the major plantations run by the companies who adopt chemical weed control close to 80% of their cultivated extents due to heavy labour shortage.

4. Total tea cultivation extent of the Island approximates 0.21 m ha of which around 40% is managed by the large plantation companies while the rest 60% by small holders. Among the key issues relevant to management of tea plantations, effective control of weeds in both young plantations and after pruning is vital for sustained production. Although a large number of labour is required for manual weeding, because of the heavy shortage of labour in the tea sector, manual weed control has become almost insufficient incurring a considerable reduction in the profit margin for the producer. The reasonable alternative is the adoption effective herbicides along with supplementary manual weeding.