eChapters

INTRODUCTION

Control of weeds below economic threshold level in potato crop is a substantial component of crop management strategy for achieving optimum productivity. In our country, potatoes are raised eitherin assured irrigation or as rainfedcrop with comparatively heavy doses of fertilizers. Therefore, weedsarebound to become menaceduringactive cropgrowth period of this cropand theseundesired plants needs to be controlled in early stages of crop growth by adopting several techniques. Current scenario of crop production is different from past due to manyreasons. Farm holdings are becoming smaller day-by-day and majority of potato growers are small and marginal farmers. They have limitedcapacity for purchase of inputs and farm machines. They need economical, efficient and easier to adopt weed control technologies.Farm labour is also costly nowin many regions as they are migrating towards cities and industrial townships. This scenariobecomes more complex as weeds would be major challenge due to global warming, which is slowly changingclimatesof potato growingregions in India.Theconcern forenvironmentalissuesemphasizeuponadoptingsystems and integrated approach for managing weeds in such away that thesedo not reducethe potato and system productivity (CPRI, 2014).

Objectives

1. To study the weeds and its control.
2. To study the herbicides, their types, timing and methods of application.

Weed: A wild plant growing where it is not wanted and in competition with cultivated plants.

Or

Weed is such undesirable plant grown in association with crop which snatches major parts of nutrients, water, light, place and CO₂ available to the crop.

Due to tough competition crop suffers adversely and the production is reduced.

Most of us consider weeds to be the troublesome, competitive, aggressive, undesirable, unsightly elements of the plant world. We hate weeds since desirable plants cultivated by us are deprived of food, water, sunlight and space by these plants. They can easily colonize an area and thrive even under non-ideal conditions of growth and may affect human welfare adversely. It is perhaps due to this that the saying, when weeds win all the people lose, has come into existence.

The terminology committee of the Weed Society of America gives the simple definition of weed as a plant growing where it is not desired. King (1974) in his book Weeds of the World observed that ‘‘a plant classed as a weed in one region where it has few, if any, uses may when growing in another region, possess some very valuable uses, or in few cases may actually be cultivated’’. For instance, Bermuda grass (Cynodon dactylon) is a highly troublesome weed in crop fields, but in village pastures, it is a much sought for forage grass. Quack grass (Agropyron repens) is a very good soil binding grass on erodable non-crop lands but it is a serious weed when it infests crop fields and orchards. Campbell (1923) considered weeds as ‘honest, independent competitors for food materials in the struggle for existence’. He pointed out that the term, weed has developed in the minds of people not according to specific qualities or by a definite concept in the mind of man, but by human caprice, e.g., corn is a cultivated crop, hence, desirable plant in a corn field. However, if a corn plant grows in a Soya bean field, it is considered a weed by the Soyabean farmer. Sometimes, two persons may differ about the weedy nature of a plant at the same place and time, e.g., water hyacinth (Eichhornia crassipes) is a weed for fisherman but it is a plant of aesthetic value for a city dweller.

Thus, a corollary to the above definitions of weed is that weeds are those plants, which grow out of their place, interfere with the utilization of natural resources, prolific, persistent, resistant, competitive, harmful and even poisonous in nature and can grow under adverse conditions.

Weed management practices are evaluated for its efficiency in terms of effective control of weeds and economics of control measures through various indices under sole crop situation as well as intercrop situation.

6.1. Indices for Sole Crop Situation

The absolute effect of particular method or a chemical in reducing the weed competitions and increasing the crop productivity are measured effectively by various indices. The comparisons of weed control methods are usually based on the yield, weed population and weed dry matter from the control as well as treated plots.

With Judicious Use of Herbicides

Herbicides are the chemicals used for killing or suppressing the growth of weed plants from field / horticulture / plantation crops as well as non-cropped areas/ water bodies etc. The herbicide is said to be an ideal herbicide when it is very safe to the crop on which it is applied and on the other hand, it must control all associated weeds effectively. Also, ideal herbicides should leave no residual effects on the succeeding crop(s). Herbicides are of two types i.e.

1. Selective herbicides and
2. Non-selective herbicides.

A selective herbicide is that which is very safe to crop plants but unsafe to weed plants e.g. atrazine in maize, clodinafop in wheat etc. On the other hand, non-selective herbicides are those which kill all green plants including crop and weed plants which come in their contact e.g. paraquat and glufosinate ammonium.

Onion is highly vulnerable to weed competition because of its slow early growth, shallow roots, narrow upright leaves and limited canopy development. Weeds compete for light, water, nutrients and space while also harbouring pests and pathogens. Severe infestation during the critical competition period can cause substantial yield reduction. This chapter describes major onion weeds and evaluates cultural, physical, mechanical, biological and chemical control methods. Timely planting, suitable spacing, mulching, raised beds, manual weeding, mechanical tools, herbicides and biological agents are discussed. Integrated Weed Management is recommended as a smart approach combining complementary methods to improve weed control, protect soil health and sustain onion productivity.

Weed management in natural farming emphasizes natural, chemical-free methods that align with ecological principles. Instead of using herbicides or synthetic chemicals, natural farming promotes approaches that maintain biodiversity, improve soil health, and reduce weed pressure through various cultural, mechanical, and biological methods.
Here are key strategies for weed management in natural farming:
1. Mulching
Mulching is an agricultural and horticultural practice in which organic or inorganic materials are spread over the soil surface to protect and improve soil quality. In natural farming, mulching plays a key role by fostering a healthier ecosystem for plants without synthetic inputs.
Types of Mulch
Mulches are broadly categorized into organic and inorganic types:
• Organic mulch includes materials such as straw, leaves, grass clippings, crop residues, compost, wood chips, and sawdust. These materials decompose over time, enriching the soil with organic matter and nutrients.
• Inorganic mulch consists of materials like plastic sheeting, landscape fabric, and gravel. While these do not decompose, they effectively suppress weeds and retain moisture but do not improve soil fertility.

Weed

Weed in orchards reduce crop yields by competing for moisture, nutrients, light and space. They also harbour insect pests and diseases. When they become large they interfere with orchard operations. Some of weeds climb on the trees and shade the foliage. There are some weeds which are parasitic partially or completely on the host tree e.g. Striga and loranthes on mango.

Site-specific weed control technologies practiced in precision farming are defined as machinery or equipment embedded with technologies that detect weeds growing in a crop and take action to maximise the chances of successfully controlling them taking into account predefined factors such as economics.Some of the commercial hardware and software developed for precision agriculture practices comprise tools for weed mapping and control software that adapts spraying to local weed occurrence. However, few farmers have adopted sitespecific weed management, although several studies have shown that weed occurrence and density varies significantly within a farm or a field. Site-specific weed control techniques have gained interest in the precision farming community over the years. Managing weeds on a subfield level requires measuring the varying density of weeds within a field. Decision models aid in the selection and adjustment of the treatments, depending on the weed infestation. The weed control can be done either with herbicides or mechanically. A site-specific herbicide application technology can save large amounts of herbicides. Mechanical weed control techniques adapting to the weed situation in the field are applicable to a wide spectrum of crops.

A system for the discrimination of different weed species and crops from images is done which generates weed maps automatically. Models for the yield effect of weeds are developed and applied in on-farm-research experimental setups. Economic weed thresholds are derived and used for an herbicide application with a patch sprayer.Herbicide use has not eliminated weed problems in agriculture and the need for manual weed removal is still an issue within specialty crop systems, particularly during the first several weeks of crop emergence when competition for resources is greatest.

Precision agriculture is a powerful technology with potentially important applications to weed management. However, growers should remember good agronomic practices, including preventing weed infestations, managing herbicides wisely to prevent resistance, and minimizing environmental impact associated with weed management. Weeds, and methods used to control weeds, can have negative economic and environmental impacts. With precision agriculture, growers can take advantage of the patchy nature of weeds by targeting management efforts only where they are needed instead of wasting expensive and potentially hazardous inputs where weeds are not present. Weeds are patchy because weed spread, survival, and reproduction are variable within a field and over time. Weed patches stay in about the same place from year to year, even though weed density within a patch may vary

Weed

Definition: “Weed is an unwanted plant growing where it is not desired.” – Jethro Tull

Commonly noticed weed species in fruit orchard:

• There are more than 30,000 species of weeds distributed world over, out of which 18,000 are noxious and cause serious losses.
• Around 250 species are causing serious economic losses.
• Monocot weeds (Narrow leaf/Grasses): Cyprus, Cynodon, Poagrass, Rye grass, Quackgrass etc.
• Dicot weeds (Broad leaf weeds): Dandelion, Chenopodium spp., Parthenium, Solanum, Euphrobia spp., Ground ivy etc

Symbolic to its nomenclature, ’PULSE’ (P = people, U = umbrella, L = livestock, S = soil and E = energy) is a superb group of agricultural crops extending an energy umbrella to people (as a major source of dietary protein), livestock (as a green nutritious fodder and feed) and soil (as a builder and restorer of soil fertility through biological N₂ fixation). On account of these qualities, pulses have occupied a unique position in the Indian farming system. Crop diversification with greater inclusion of legumes is essential to alleviate declining factor productivity, input use efficiency and increasing cost of cultivation for realizing sustainable use of natural resources. Pulses are increasingly becoming a component of the intensive cropping systems as intercrop, substitute crop or catch crop. In upland situations, pulses play an important role as intercrops and ensure more income and efficient use of resources. While analyzing the reasons of low productivity of pulses in various parts of the country, it is observed that non availability of high yielding disease resistant varieties, cultivation on marginal and sub-marginal lands under deficit moisture and fertility and poor pest management are the major constraints in realizing optimum yield potential.

Different crops are grown in a field. Any plant growing in a place where it is not desired competing with the main crops, has to be weeded out and such plants are called ‘weed’.

Effect of weed menace The weeds

Reduce crop yield and production efficiency. It competes with the main economical crop for space, water and nutrients.

Reduce crop quality.

Hamper intercultural operations.

Reduce crop quality.

Obstruct the flow of water in the irrigation channels.

Exert allelopathic effect on crops.

Harbour insect and pests, which affect the main crop of interest.

Increase the cost of production.

13.1 INTRODUCTION

Weed is defined as an unwanted plant growing at a place where it is not desired. Weeds are unwanted and undeserved plants that interfere with the utilization of the land and water resources and thus adversely affect crop production and human welfare. Thus, a plant out of its place or a plant growing where it is not desired at that time is a weed. Weed has no species, but name was suggested as a useless and harmful plant that persistently grows where it is quite unwanted. According to Jethro Tull, the father of Weed Science, weed is defined as the unwanted, undesirable plant, growing out of their proper place, which interfere with the utilization of natural resources, prolific, persistent, competitive, harmful and even poisonous in nature and can grow in adverse climatic conditions. Of the total losses caused by pests, weeds have a major share (30%). They reduce the crop yield and decrease the quality of produce and hence reduce the market value of the turnout. Weeds are a major problem to horticultural production as they take advantage of their initial slow growth rate. Weeds reduce crop yield, lower their quality, act as alternate host of many pests/diseases and also have allelopathic effects on crops. Weeds also interfere with vital farm operations like weeding, fertilizer application, herbicide application and harvesting. Both annual and perennial weeds are common in their actions reducing the productivity of fruit trees. Weeds also provide shelter to various pathogens by becoming an alternate or collateral host of invaded crops by a number of fungal, bacterial and viral diseases.

The worst weeds found in the world are Cyperus rotundus, Cynodon dactylon, Echinochloa crusgalli, Echinochloa colona, Eleusine indica, Sorghum halepense, Imperata cylinderica, Eichhornia crassipes, Portulaca oleracia, Chenopodium album, Digitaria sanguinalis, Convolvulus arvensis, Avena fatua, Amaranthus hybridus, Amaranthus spinosus, Cyperus esculentus, Paspalum cojugatum, Rottboelia exaltata (Rana and Rana, 2016). All of these weeds are found in India. It has been reported that about 36-42% losses may occur due to inadequate management of weeds in apple (El- Metwally and Hafez, 2007). Therefore, management of weeds in all agro-ecosystems is crucial to sustain our crop productivity and to ensure the food security to the rapidly increasing population.

Abstract
Legumes are an excellent group of fertility restorer crops which can be grown either as sole crop or as a component crop in the cropping system. As they are tolerant to drought condition, they can be grown throughout the year. The yield of legume crop is largely depending on pest, diseases and weeds. Among these weeds plays a major role as the weed seed bank inside the soil influence the weed population in the cropping season. Hence it is important to manage the weed seed bank for better productivity of legumes. Though legumes are short duration and fast growing crops, the germination percentage of weed seed bank will determine the final yield of legumes. There are many strategies to which the weed seed bank can be controlled to tolerable level before which the weed seed bank present in the soil has to estimate. Annual weed seed bank can be minimized by killing the weeds before they set seeds, harvest weeds, crop rotation, cover crops, inter cropping and ensiling. Weed seed bank depletion can be done by tillage, tricking the weed seeds, conditioning weed seeds, soil solarisation and herbicide application. Thus integrating various technologies may help in effective controlling of weed seeds to tolerable level thereby enhancing the yield of leguminous crops.
Keywords: Estimation of weed seed bank, legumes, tillage, yield, weed seed bank

Shifts or changes in the abundance and types of weeds within agricultural systems are common. These shifts can occur for a number of reasons and may result from cultural, mechanical, or chemical weed management strategies. The right combination of weeds and relying too heavily on any one practice is often the most common cause. Some of the concepts associated with weed species shifts are discussed below.

A weed shift is the change in the composition or relative frequencies of weeds in a weed population (all individuals of a single species in a defined area) or community (all plant populations in a defined area) in response to natural or human-made environmental changes in an agricultural system. Weed shifts occur when weed management practices do not control an entire weed community or population. Some species or biotypes are killed by (or susceptible to) the weed management practice, others are not affected by the management practice (tolerant or resistant), and still others do not encounter the management practice (dormant at application).

Those species that are not controlled can grow, reproduce, and increase in the community; resulting in a weed shift. Any cultural, physiological, biological, or chemical practice that modifies the growing environment without controlling all species equally can result in a weed shift. Weed shift may be due to introduction of new species or change in relative proportion of members of the existing community. Latter is the most common.

A. Species shift: Change in density of one or more species in field

B. Biotype shift: Change in density of biotypes within a species. These shifts often found noticed since biotypes typically are similar in appearance. Herbicide resistantbiotypes are the most frequently studied.

Weed monitoring is conducted to detect significant weed problems, rank them for relative severity and sort them by management type annuals, biennials, perennials, grasses and broadleaves. Weed monitoring provides information to tailor weed management efforts that reduce the impact of the weeds. The primary objective of weed survey and mapping is to accurately identify and delineate land with populations of unwanted plants. These surveys are conducted so that scientists and managers can predict those areas potentially subject to weed invasion; understand the biology of the invasion process and determine means by which weeds spread; develop, implement and evaluate weed management plans; assess the economic impact of weed invasion and increase public awareness, education and weed management efforts. Weed survey information is collected and compiled into maps showing the distribution and severity of infestation. Weed monitoring involves repetitive surveys to track weed populations over time. A standardized system of weed surveying and mapping is necessary to provide consistently reliable information that can be compared from year to year. Further, a standardized system allows weed survey data to be incorporated into a state wide weed survey database for the production of state wide noxious weed maps.

5.1 Weeding and Interculture Equipment

The aim of weeding and intercultivation operation is to provide best opportunity to crop to establish and grow vigorously up to time of maturity. The main objectives of weed control are to improve the soil conditions by reducing evaporation from the soil surface, improve infiltration of rain or surface water, and reduce runoff to maintain ridges or beds on which the crop is grown and to reduce competition of weeds for light, nutrients and water. Mechanical methods of weed control are simple and easily understood by farmers. The tools and implements for mechanical weed control are mostly manual and animal operated. Manual method is most effective but is slow. It is popular in regions where labour wages are low and labour is easily available during the season. The additional cost of weeding using implements is comparatively less than the gains due to extra yields obtained. First weeding operation is mostly done between and along the rows. Remaining operations are done mostly between the rows. Hand hoes are generally used for removing weeds between plants in a row.

19.1. Need for weeding

Weeding is the critical operation to be carried out to obtain a good crop. Weeds are plants which grow in places where they are not wanted. They grow in the fields competing with crops for water, soil nutrients, light and space and thus reduce crop yields. They also harbor insect pests and micro-organisms. Certain weeds release the inhibitors or poisonous substances into the soil which are harmful to plants, human beings and livessecks. They increase the expenditure on labour and equipment, render harvesting difficult and reduce the quality and marketability of agricultural produce. When grown in water channels, they block and or reduce the flow of water.

The weed seeds germinate earlier and grow faster than the crop plant. This phenomenon is more pronounced when coupled with favourable environment like fine soil tilth and the soil receiving adequate water and fertilizers. Weeds flower earlier and produce seeds profusely ahead of the crop. So, these seeds get mixed up with the harvested crop and are distributed to the next season or transported to other places along with the harvested produce.

An agricultural weeder is a tool designed to remove weeds from fields or gardens. It can be used manually or attached to machinery like tillers and power weeders. Weeding is necessary to eliminate unwanted plants that compete with crops, ensuring better growth and profitability. Effective weed management is crucial in crop production, as weeds can reduce yields by stealing nutrients and attracting harmful pests. In recent years, research has focused on non-chemical methods and environmentally friendly alternatives to herbicides for weed control. Mechanical weeding is often the most cost-effective solution. Tools like rotary weeders, mechanical hand weeders, and wetland weeders are generally effective, with wetland versions gaining popularity due to their ability to function in shallow water. These tools uproot weeds and bury them in the mud through their pull-and-push action, making them both safe and eco-friendly. Weeding should be done at least three times during a growing season, with early weeding being the most effective for completely eliminating young weeds.
FUNCTIONS OF WEEDING EQUIPMENT
Secondary tillage equipment is often used for weed management. Weeders help control weeds between planted crops or before sowing. Some weeding machines use mechanical methods to remove unwanted plants without the need for chemicals.
Usage Instructions
• Early weeding is essential: Perform the weeding within 20 days after sowing.
• Delayed weeding can lead to competition between paddy and weeds, harming the crop.
• Move the weeding machine back and forth between rows.
• Conduct a second round of weeding after 15 days, and if possible, a third.