Grassy Weed Control in Direct-Seeded Rice Fields

Security of food and livelihood is greatly aided by rice production. The depth of weed infestation, weed shift, and yield losses in dry DSR (DDSR) will all be discussed in this blog post. We will also go through effective weed control tactics that can be used to lessen these difficulties, emphasizing combining preventative, cultural, mechanical, and chemical weed control methods.

We seek to offer insights into the effective control of grassy weeds in direct-seeded rice fields, notably in South Asia, by looking at regional and international activities in DDSR. By implementing region-specific weed management techniques, Asia could reduce pesticide use by up to 50% in DSR areas, which now account for 22% of all rice agriculture.

Grassy Weed Control in Direct-Seeded Rice

What are rice fields with direct seeding?

Direct-Seeded Rice (DSR) is a technique for planting rice seeds straight into soil that isn't wet or puddled. It is a substitute for transplanted puddled rice (TPR), which needs a lot of water, energy, and work. Rapid planting, simple mechanization, lessened labor and water requirements, and early maturity with minimal environmental impact are only a few benefits of DSR. In Asia, DSR has grown in favor and now occupies roughly 22% of all rice land.

Weed control is one of the key issues with DSR since weed infestation can result in yield reductions of up to 75%. In DSR, weed control can be achieved manually, using herbicides, or through a mix of both. Herbicide use has generated questions because of issues with weed resistance, alterations in weed density and composition, and detrimental impacts on the environment. For long-term weed control in DSR, comprehensive weed management strategies are advised to solve these issues.

DSR has demonstrated varying yield responses and water productivity depending on the region and agronomic treatment. Productivity values ranging from 7.3 to 10.3 tons per hectare have been documented in various locales. Despite these difficulties, DSR has the potential to save money on labor and water; thus, it is crucial to research weed control methods unique to your location.

Read also: The Ultimate Guide to Water Management and Irrigation for Greenhouses

In Direct-Seeded Rice Fields, Grassy Weeds

Direct-seeded rice (DSR) has become increasingly popular because of the reduction in water availability brought on by climate change and the labor crisis in agriculture. This change is a result of the traditional flooded transplanting method. 

DSR has advantages, including conserving water, speeding up the maturation process, requiring less effort, and having a smaller environmental impact. But in DSR, weed invasion poses a significant problem that could result in up to 50% output losses.

Direct-Seeded Rice (DSR) fields have a considerable challenge from grassy weeds. Out of the 161 million hectares used for paddy agriculture, over 33 million hectares worldwide use DSR. 

In DSR, several sowing techniques are employed, such as directly broadcasting dry seeds, dribbling sprouting seeds, and line sowing. In DSR, weed development is encouraged by the lack of stagnant water and a head start for rice plants. 

A weed-free environment till 70 days after sowing is preferred for increased yield. Weed competition is still important up to 41 days after sowing.

After insufficient water supply, poor weed control is the second largest yield obstacle in DSR. The weed effect can reduce yield by anywhere from 18% and 100%, with traditional transplanted puddled rice (TPR) reporting an average yield loss of 35% and DSR reporting even higher losses of up to 100%. 

In the case of rice, weeds are responsible for around 10% of all yield losses, a figure that rises to 32% in DSR. In the shift from TPR to DSR, weedy rice, a harmful weed species closely similar to cultivated rice, has emerged as a significant danger. 

It has been documented in several nations across continents and results in considerable quantitative and qualitative losses to rice output.

The adoption of DSR has changed the makeup of weeds, with grassy weeds predominating over traditional tillage-based rice farming. 

DSR fields generally have a higher weed species diversity than TPR fields, with more grassy and broadleaved weed species. 

Particularly in Southeast Asian countries, DSR fields have changed through time to favor more aggressive, competitive grasses and sedges. The sowing and tillage techniques affect how much weed seed bank build-up occurs.

Typical Grassy Weed Types in Rice Fields

In rice fields, several common grassy weeds can seriously reduce crop output. These weeds reduce yields by competing with rice plants for essential resources, including water, nutrients, and sunlight. Echinochloa crus-galli (barnyard grass), Leptochloa chinensis (Asian sprangletop), and Fimbristylis militia (common fimbria) are a few of the grassy weeds that are frequently discovered in rice fields.

These weeds' adaptable traits, like quick growth, high tillering capability, and effective nutrient uptake, enable them to flourish in rice fields. Due to its aggressive character and intense competition with rice plants, barnyard grass is particularly infamous. Effective management techniques are required to eliminate these grassy weeds and reduce yield losses, such as using herbicides, hand weeding, and cultural approaches. 

Grassy weeds' life cycle and growth characteristics 

True grasses or monocots, which include grassy weeds, have unique life cycles and growth traits. For control methods to be effective, it is essential to comprehend these qualities. 

Annual weeds go through all life cycle stages in a single year, including seed germination, growth, blooming, seed production, and death. While warm-season grasses like crabgrass and goosegrass grow in the spring and thrive in the summer and early fall, winter annuals sprout in the fall, flourish in the winter, and die in the late spring or early summer.

In contrast, perennial weeds have more than two years of lifespan and can reproduce both by seed production and vegetative elements like tubers, bulbs, rhizomes, or stolons. Due to their durability and abundant reproductive potential, perennials provide considerable hurdles.

The annual bluegrass (Poa annua), a cool-weather annual that emerges in the fall, survives through the winter, develops seed in the early spring, and perishes in the late spring or early summer, is one typical grassy weed. 

Both goosegrass (Eleusine indica) and crabgrass (Digitaria species) are summer annuals germinating in the spring and producing seeds from mid-summer until the end of the growing season before being killed by the first fall chill.

These grassy weeds need to be controlled using a variety of techniques. Mulching, correct fertilizer, and enhancing lawn health are examples of cultural activities that can be helpful. In addition, depending on the type and timing of the turfgrass, pre- and postemergence herbicides are available.

Grassy Weeds in Rice Fields: Identification

Monocot plants that resemble genuine grasses are called grassy weeds. They sprout from the germination of seeds and have a single leaf. The stems have closed, rigid nodes and are hollow and spherical—the parallel veins and length and width of the leaf blades. Pay attention to the plant's texture, color, and growth pattern. Farmers may differentiate grassy weeds from the rice crop by carefully studying these characteristics and implementing the right control measures to lessen their negative effects on yield and quality.

Fields of Direct-Seeded Rice Are Important

First, direct seeding removes the time-consuming and expensive process of transferring seedlings. With this technique, planting can start sooner, and yields could be higher. 

Direct sowing also encourages better weed management since rice plants develop quickly and outcompete weeds more successfully. 

Additionally, they have better water management because direct-seeded rice fields can be flooded later, lowering water use and increasing water efficiency. 

This approach also permits equipment utilization, allowing for mechanization and raising output. 

Direct-seeded rice fields offer a more effective and economical rice-growing method, boosting agricultural productivity and promoting sustainable farming.

Grassy Weeds' Effect on the Rice Crop

Rice fields are seriously threatened by weeds, which dramatically lowers agricultural production. Weed infestation can typically cause yield reductions of 15% to 20%. Depending on the kind and quantity of weeds present, these losses may, in extreme situations, surpass 50%. When rice is transplanted, a wide variety of grasses, sedges, and broad-leaved weeds are present, resulting in yield decreases of up to 76%.

Even at high concentrations and for extended periods, certain weed species cause less damage than others in yield loss. Overall, weed competition can reduce rice yields by 40 to 60% on average, and in the worst circumstances, unchecked weed development can cause yield losses of 94 to 96%.

Monitoring of New Weed Species' Appearance in Direct-Seeded Rice Fields

Alternanthera triangle has emerged, a new weed that has taken over almost 70% of the space of Chhattisgarh's direct-seeded rice fields. Malwa pusila, Cenchrus ciliaris, and Chromolaena odorata were also encroaching on weeds in the Chhattisgarh plains, and they were coming from the state's southern regions. A vigorous emergence of Celosia area was observed in Kharif direct seeded rice in 2015, during the sixth year of a long-term herbicide study in a DSR-chickpea cropping system, which resulted in the suppression of Alternanthera sp. in the initial stages of crop growth.

Approach to Integrated Weed Management (IWM)

Because both crops and weeds grow simultaneously, grassy weeds pose a serious threat to direct-seeded rice fields. Herbicide resistance and yield reductions can result from relying primarily on chemical weed control. For efficient weed control in direct-seeded rice fields, integrated weed management (IWM) combines a variety of methods.

Preventive Weed Control Techniques

Prevention of Weed Seed Dispersal: Keeping weed seed banks to a minimum and stopping fresh weed seeds from entering crop fields is essential. Effective agronomic techniques, including induced predation, fatal germination, tillage, and submersion, aid in depleting current weed seed stocks.

Using clean, weed-free agricultural seeds is essential to reducing weed intensity and the risk of seed contamination. Herbicide resistance can be propagated via contaminated weed seeds, and new weed species can be introduced.

Cultural Weed Control

Unfresh Seedbed

Using non-selective postemergence herbicides, emergent weed seedlings are eradicated using the stale seedbed (SSB) cultural technique. In addition to lowering weed densities and viable seed banks, SSB is effective against weedy rice. Additionally, it lessens the required labor and encourages the development of some weed species for later killing.

A Prepared Land

Through uprooting and burying weeds, tillage operations can reduce weed emergence and growth. Tillage changes the edaphic environment and the water and gaseous regimes, which causes dormancy induction and the death of weed seedlings. A weed-free seedbed is provided, weed densities are decreased, and pesticide use efficiency is increased with proper land preparation, which includes laser ground leveling.

Increasing crop competition

The selection of rice cultivars with vigorous early growth, quick ground cover, increased specific leaf area, and root and shoot features that improve competitiveness against weeds is critical. Plant Type and Crop Cultivar. More sun energy is captured by cultivars with horizontal leaf arrangements, which reduces weed competition.

Seed priming procedures, such as hydro-priming, solid matrix priming, and nutri-priming, enhance the seedlings' vigor and ability to withstand stress.

Plant Population Dynamics via Crop Geometry and Seed Rate: Weed competitiveness may be improved by raising seed rates and population densities. Higher seed rates enhance crop performance while reducing the need for herbicides.

Grassy Weed Control in Direct-Seeded Rice Fields

Direct-seeded rice fields are seriously threatened by grassy weeds, which affect crop development, productivity, and quality. To reduce these harmful impacts, it is essential to put in place efficient weed management strategies.

Controlling weeds is crucial because they directly compete with rice plants for resources like water, nutrients, and sunlight, which lowers yields and raises production costs. Additionally, weeds lower the grain quality, which hurts the price farmers receive for their harvest.

Ground Preparation: Good ground preparation is important in lowering weed pressure. To allow for weed growth, begin land preparation 3–4 weeks before planting. Before planting, the land should be repeatedly plowed and harrowed to assist in removing any weeds and crop residue.

Weed Emergence: For wet-seeded rice, give weeds at least two weeks to grow before shallow tillage is used to kill them. This limits weed growth in the succeeding crop and lowers the soil's weed seeds. Allow weeds to appear in dry-seeded rice within 1-2 weeks, then remove them with non-selective herbicides or light management.

Stale Seedbed Technique: This technique successfully lowers the soil's weed seed bank. To put this strategy into practice, perform tillage procedures, including plowing, harrowing, and leveling the field. Encourage the emergence of weeds by lightly watering or raining. Kill the sprouting seedlings by spraying non-selective herbicides on them or using light cultivation. Crop planting without additional tillage is preferable if soil conditions allow it since additional tillage may encourage weed germination.

Application of Herbicides: Herbicides should be used with other weed-control strategies, including cultural techniques, hand weeding, and mechanical weeding. Several herbicides should be sprayed at particular growth phases for efficient weed management. While pre-and postemergence herbicides focus on weed seeds and young plants, pre-planting herbicides can remove already-existing vegetation.

Modern Methods and Tools for Grassy Weed Control in Direct-Seeded Rice Fields

New methods and technologies have been developed to tackle grassy weeds in direct-seeded rice fields due to weed management advancements. These include weed infestation mapping and identification techniques used in precision farming, such as remote sensing and satellite imaging. To improve weed control, integrated weed management strategies combine cultural techniques like crop rotation and cover crops with targeted herbicide applications.

Creating rice types resistant to herbicides also enables selective weed management without endangering the crop. Adopting robotic devices for automatic weed detection and removal is a further step toward effective and precise weed management. These cutting-edge methods and tools have enormous potential for enhancing weed-control tactics and raising rice output.

Conclusion

For direct-seeded rice fields to produce their highest yields, with the lowest production costs, and with the highest quality grain, grassy weeds must be well managed. Successful weed management and increased crop output can be achieved by employing modern technology, cultural methods, and herbicides.