Weed Management in Direct-seeded Rice System

Dr. Manoj Kumar Subject Matter Specialist (Agronomy) Krishi Vigyan Kendra (KVK), Longleng   Weed management is the major challenge in direct seeded rice/upland rice. In direct seeded rice (DSR) weed emerge simultaneously with crop seedling and grow more quickly in moist soil than in  Practice of Transplanted Rice (PTR) (Khaliq and Matloob, 2011), resulting in severe competition for resources to the crop. Therefore, weeds present the main biological constraints to success of DSR and failure to control weeds result in yield losses ranging from 50-90 %. Traditional methods of weed control in rice include hand weeding by hoe or hand pulling, but this has become less common because of labour scarcity at critical time of weeding and increasing labour costs. Moreover, seedling of some grassy weeds such as Echinochloa crusgali (L) look similar to rice seedling, making hand weeding more tedious, difficult and less effective. Weeds compete with crops for solar radiation, nutrient and soil moisture when they are limiting and the early season competition is the most critical. When improved agricultural technologies are adopted, efficient management becomes even more important for obtaining the maximum productivity and benefits. Predominant weed species observed in the experimental field during rainy season Cuphea balsamon, Borreria hispida, Ageratum conizoides, Spilenthes spp., Drimaria cordata, Erecthritis valerianifoliaamong broad-leaved weeds; Paspulumum congugatum, Paspulum longifolium and Digiteria sanguinalis among grasses and Cyperus rotundus and Eleisine indica among sedges. A single weed control approach may not be able to keep weeds below the economic threshold level, and may result in weed flora, resistant development and environmental hazards. Therefore, adoption of diverse technology is essential for weed management because weed communities are highly responsive to management practices. The diverse technology of weed management is as follows  

1. Preventive measures

Weeds are generally brought to the crop field by a number of carriers. If the introduction of weed propagating materials is stopped, weed problem can be solved and the crop will grow with less competitions. Following are the preventive measures to check the weed seed/propagating material to enter into the field.

• Using certified seeds free from weed seeds
• Using well rotten manure
• Cleaning farm boundaries
• Cleaning irrigation canal/channels etc.
• Controlling weeds before flowering/seed setting
• By weed laws
• By Quarantine laws

  B Control measures

1. Cultural method

• Proper crop stand or plant population: Higher plant population and optimum spacing results into lower weed dry matter. In jhum rice can be sown by dibbling and line sowing method with spacing of 25 cm x15 cm and 25 cm apart respectively, which help for interculture operation.
• Intercropping: Intercropping results into more crop canopy coverage and higher plant population density, thus it results in better suppression of weed growth. Intercropping reduces weed growth particularly in widely spaced crop. Planting quick growing crops in between the widely spaced crop rows helps in smothering weeds and provides extra returns. However reduction in weed growth depends on nature of intercrop, their relative proportion and the spatial management of the plants. Commonly grown intercrops are cowpea, groundnut, greengram, blackgram, soybean, pea etc.
• Land preparation: Tillage serves to provide a suitable soil tilth for a seed bed and control weeds prior to crop establishment.

   

1. Mechanical or Physical method

• Hand weeding: Hand weeding is the most widely used weed control method. However, it is back breaking, tedious and economically not feasible.
• Hoeing: Pulling by hand/using tools like hoe, spade or small blade harrow 2-3 times. It is highly effective against weed seedlings of both annuals and biennial weeds.

    iii. Chemical weed control: Weedicides offer the most effective, economical and practical way of management. Chemical weed management may be possible in jhum also. Pre-emergence herbicides can be use for controlling of weed (2-3 DAS of crop) in jhum field. Mixed cropping is followed in jhum field therefore post emergence herbicides may not be use. However it can only be use when the entire jhum crop can be sown separately. Post emergence herbicides are selective for selected crop. In jhum, rice is predominant crop, therefore rice can be sown alone in large area and other crop in small area separately then post emergence herbicides may be used in rice crop only for controlling of weeds. In large scale rice farming, herbicide based weed management has become the smartest and most viable option. Herbicides may be considered to be a viable alternative to physical and cultural methods. A list of commonly used herbicides in direct seeded rice/upland field with active ingredients, application time and target weed groups has been presented in table 1&2.       Advantages of chemical weed control

• Herbicides ensure efficient control of weeds particularly during the critical period of crop weed competition.
• Herbicides substantially reduce labour requirement and helps in productive use of labour.
• Weed control through herbicides is economic, particularly when labour is expensive.
• Herbicides reduce the number of tillage operation needed for crop establishment.
• Herbicides enable management of weeds under unfavourable soil and climatic conditions.
• Herbicides allow timely/early planting of crops.
• Mechanical damage to the crop is reduced with herbicides.
• Crop root injury can be avoided with herbicides

  Limitation of herbicides Herbicides are only one type of weed control tool. Because of effectiveness of herbicides there may be over reliance on herbicides and other methods such as prevention, sanitation, cultural practices, crop competition and rotations are overlooked as viable option. Some of the potential limitations are:

• Injury to non target plants/vegetation
• Crop Injury
• Residues in soil and water
• Toxicity to non-target organisms
• Concern for human health and safety
• Weed shift, development of resistance in weeds

 

1. Integrated weed management

Integrated weed management is defined as the combination of two or more weed control methods at low input levels in order to reduce weed competition in a given cropping system below an economical threshold level. It is physically an integration of effective, dependable and workable weed management practices that can be used economically by the producers as a part of sound farm management system. This method is a combination of direct and indirect methods and provides efficient economical and sustainable control of weeds. Strategy is basically aimed to have benefits of every method and to overcome problems related with the over reliance of any particular method. Repeated application of same herbicides is known for development of resistant in weeds besides causing weed shift in a particular cropping system. As for example, pre emergence application of pendimethalin 1.0 kg/ha with hand weeding at 25 DAS significantly reduced the weed biomass and increased the yield of both the crop in rice + greengram intercropping system. In upland direct seeded rice, pre-emergence application of butachlor 1.5 kg/ha or pentilachlor + safner (0.75 kg/ha) followed by mechanical weeding at 30 DAS was effective in controlling in weeds.   Conclusions: Weed management is the most important for any crop. Land area under DSR system is expected to be increase in future because of labour and water crisis. Weeds are the major constraints to DSR and its management, failure of which may result in severe losses in terms of yield and economic return. Therefore, integrated approaches of weed management with rotation of herbicides with different mode of action followed by manual weeding are suggested for sustainable weed control in DSR.