eChapters

Weeds are diverse plant species of the ecosystem which can survive adverse condition and reproduce quickly. The global compendium of plants has listed 28000 species as weeds. According to Holm et al (1977) about 8000 weeds species have been reported from agricultural fields in 124 countries and of these, 250 species are considered to be problematic. It is also to be noted that weeds from 12 families constitute 68% of the world’s worst weeds. Within these 12 families, weeds from poaceae, asteraceae and cyperaceae constitute 44% of the world’s worst weeds.

Weeds have specific characters which helps them to adapt to any stressful situation and successfully, compete with the crop. They have survival strategies which help them to overcome vagaries of nature like extreme cold, heat, drought, biotic stresses and soil abnormalities. Their most important characteristic is the ability to succeed in any adverse situation even in disturbed soils. The age old war between man and weeds makes it pertinent to understand the characteristics of weeds which make them better competitors in the field.

Weeds have been a problem to agriculture ever sine man started cultivation. Weed species by and large invade cropped areas and account for large economic losses to the farmer. Weeds are economically more important than insects, fungi or other pest organisms (Savary et al. 2000, 2006). Globally, weeds cause the highest potential loss to crop production (34%), with animal pests and pathogens being less important (losses of18% and 16% respectively). The loss in production due to weeds has been estimated as 5% in developed countries. It is around 10% in developing countries and 25% in least developed countries. (Oerke, 2006)

Deliberate use of natural enemies to control invasive pest in an ecosystem is known as biocontrol. To control invasive weed species, selective pathogens and weed seed predators are employed to reduce the population of the weed to non competitive numbers rather than total eradication of the weed species (Appleby, 2005) These can be insects, herbivorous fish, other animals, disease causing organisms or even competitive plants. This method is comparatively safer to the ecosystem, is cheaper and has long lasting impact. Difficulty in f inding host specific bio-agent with minimum adverse effect on other crop and the environment is a challenge.

Herbicides are chemical substances that are capable of either killing or injuring plants and so used for elimination of unwanted plants. In Latin, the term ‘herba' means plant and ‘caedere’ means to kill. There are many reasons for the increased use of chemicals for weed control. Shortage and high cost of agricultural labour prevent economic control of weeds by manual and mechanical means. Benefits offered by herbicides include efficient weed control, higher crop yield, better soil, water and energy conservation and higher income.

A large number of herbicides are currently available in the market hence selection of suitable herbicide needs judicious understanding of the product and the requirement. When large number of chemical options are available it can make the process of selection a bit confusing. So it is important to know the crops in which a herbicide can be used, the weeds it will control, the appropriate rate, adjuvants included in the formulation. The different uses of the chemical and the different situations for which it will be useful. In addition to these it is important to understand the mode of action of the herbicide and also the mechanism of action of the chemical.

Effectiveness of spray mixtures can be increased by addition of adjuvants. Weed Science Society of America (WSSA1994) have defined adjuvant as a material in a herbicide formulation or added to the spray tank to modify herbicidal activity or application characteristics. Adjuvants enhance activity of a herbicide in different ways viz., wetting, spreading, deposit building, emulsifying or deflocculating the active ingredient. In many cases cost of adjuvant will be less than that of active ingredient. In such cases it helps to reduce the cost of the final product.

Herbicides have received wide acceptance from farmers mainly due to ease of application and effectiveness. After application, herbicide molecules should penetrate plant tissue and get translocated to the target site. Once they reach the target protein they bind to them and disturb metabolic processes in plants by disrupting biosynthetic pathways and damaging cell structures by generating cytotoxic molecules that ultimately kill the plants. In this, the first step is penetration of herbicide into the plant system.

In a cropping systems there may be simultaneous or sequential application of herbicides, insecticides, fungicides, fertilizers, PGR during a single cropping season. The different chemicals will undergo physical and chemical changes as they interact with plant, soil and other chemical substances already applied to the plant or soil. The interaction effect of such chemical substances will be visible only at the later end of the cropping season. The responses observed in the plants can be.

Major advantage of chemical herbicides over other methods of weed control is its ease of application, which saves the cost of labour for the farmer. Effectiveness of herbicide depends on how long it remains in active form in the plant /soil. The form in which any herbicide is available in the market is known as herbicide formulation. The technical active ingredient (ai.) of the herbicide is converted to a formulations so as to improve easiness of handling, retention on leaf surface, absorption and movement in the plant. Herbicides are available in different formulations.

When a herbicide is applied to the soil, it is subjected to various interactions with soil and surrounding environment which ultimately determines its persistence. Dissipation of these compounds from soil system is by three main processes viz., physical (volatilization, leaching and runoff), chemical (photochemical decomposition, adsorption by organic and inorganic colloids and chemical decomposition) and biological (microbial decomposition and plant uptake) 

1. Physical Processes

a) Volatilisation

A major portion of the earth’s surface is water. Apart from the oceans, major water bodies on the earth’s surface include rivers, streams, lakes, ponds and canals. Plants adapted to these ecosystems form the aquatic species. When they pose a problem to navigation, fisheries and agriculture and also cause health hazards, they are categorised as aquatic weeds. Problems due to aquatic weeds has been reported from different parts of the world. They are common in warm waters. In Florida, it is reported that water hyacinth (Eichhornia crassipes) covers nearly 40,000 hectares of water resources.

Parasitic weeds are a major constraint in tropical agriculture. These are plants that are adapted to live on other plants sharing their nutrients and water. They constitute 1% of flowering plants, approximately 3000 - 5000 species coming under 20 families. Parasitic weeds from five families viz. Orobanchaceae, Convolvulaceae, Santalaceae, Scrophulariaceae and Loranthaceae are considered troublesome weeds as they infest economically important crops in many parts of the world and are very difficult to control by normal weed management measures.

Rice is the primary food source for half of the Asian population. Nearly 2,000 million in this region obtain 60 to 70 per cent of their calories from rice and its products. Considering the importance of the crop, United Nations General Assembly declared 2004 as the “International Year of Rice” (IYR). In India, the crop covers one-fourth of the total cropped area. About half of the Indian population use rice as their staple food.

Rice based cropping systems are not only important for food security but also for maintaing an ecological balance. Low land rice fields conserve water and prevent runoff .They preserve the sustainability of the ecosystem.

Indian tea has a global reach being the second largest tea producer in the world. Indian tea is one of the finest in the world. Darjeeling tea is the first product to get a geographical indicator tag in India. 83 % of the tea produced in India is from Assam and West Bengal and 17% from the south Indian states of Kerala, Karnataka and Tamilnadu. Weeds are a major problem in tea gardens.

Weed flora

Drymaria cordata, Bidens pilosa,, Cynodon dactylon, Panicum repens, Celosia argentea, Ageratum conyzoides, Centella asiatica, Borreria hispida, Oxalis latifolia, Mikania micrantha, Paspalam conjugatum,

Survival strategies of some plants help them to thrive in any adverse environmental conditions. We classify them as weeds or ruderals. Such weedy species have developed unique and effective physiological traits to withstand various stresses, and unique mechanisms to regulate growth under adverse environments. Climate change is a harsh reality observed in different parts of the world which brings new challenges in crop production and weed management.

Introduction of biotechnological tools in weed science and management has given new dimensions to weed research.

1.1 Introduction

Broadcasting seed and harvesting meagre yields was a common method of ancient agriculture. High use of developed crop varieties, irrigation, chemical fertilizers, pesticides and farm mechanization is the main thrust of modern agriculture. Therefore, modern agriculture is an energy intensive farming system (Khan et al., 2010). Though modern technology based agriculture is achieving success to meet food demand of increasing global population, yet it creates many environmental issues such as loss of soil fertility, salinization and water scarcity.

2.1 Introduction

Present day agriculture is facing more challenges like negative impacts of climate change, depletion of natural resources, increase of input costs etc. The major causes for steady decline in agricultural sustainability include intensive cultivation with conventional tillage practices, reduction of soil organic matter, soil loss by water and wind erosion, reduction in infiltration rate, formation of soil crust and continuous practice of mono-cropping. Over the years, soil and water resources are continuously overexploited leading to reduction in use efficiency of irrigation and energy.

3.1 Introduction

Rice is the main staple food for most of the world’s population and plays a key role to maintain food security of many countries. More than 90% of the rice production globally comes from Asia and also more than 90% of rice consumption is done in Asia (IRRI, 1997). In Asia, more than two billion people get almost 60-70 percent of their daily energy requirement from rice and its products (Yogeswari and Porpavai, 2018). As for India, since independence the country has witnessed a remarkable progress in rice production.

4.1 Introduction

Wheat (Triticum aestivum L.) is a major food security crop in South Asia, with 42% of the wheat in this region grown following rice (Oryza sativa L.) on 13.5 million hectares of land. Resource-conserving technologies offer considerable potential for improving the sustainability and productivity of wheat in the rice-wheat system of South Asia. These include raising input use efficiency, cutting costs, providing various environmental benefits, and ultimately improving farmer livelihoods and helping to reduce poverty.

5.1 Introduction

Indian agriculture is now at crossroads. We have come a long way. Over the past five decades our strategies, policies and actions were guided by goals of ‘self sufficiency’ in foodgrain production with main focus on rice and wheat. Indian agriculture has been successful in achieving higher production of food grains to secure food security of the nation. While, the success for increasing food grain production has been achieved without major jump in the production and productivity of pulses in the country, this was accompanied by widespread problems of resource degradation, which now poses serious challenges to meet the demands of an increasing population and lifting our people above the poverty line.

6.1 Introduction

The birth of modern conventional agriculture coincides with industrial revolution. The identification of N, P and K as critical factors in plant growth led to the manufacture of synthetic fertilizers. While chemical fertilizers and pesticides have existed since the 19th century, their use grew significantly in the early 20 century with the invention of Haber-Bosch method for synthesizing ammonia. The rapid farm mechanization, especially in the form of tractor and combine harvester coupled with science-driven innovative management methods and resources led to the efficiency of enabling outputs of high quality produce per unit area and time.

7.1 What is Soil Moisture Conservation Technique?

In situ soil moisture conservation means capturing rain water and retaining it in soil for utilization by plants for better growth and increase in biomass and grain yield. This is achieved through rain water harvesting on farm or field where crops are planted to get benefit from the conserved rainwater. It reduces rainwater loss through runoff and increases rain water infiltration time, thereby increasing the amount of rain water in the soil that will be useful for crop production.

8.1 Introduction

Conservation agriculture (CA) is an approach to regenerative agriculture and land management practices based on three interlinked principles: (1) continuous minimum mechanical soil disturbance using no-tillage or reduced tillage based crop cultivation, (2) maintenance of permanent soil cover using crop residues and cover crops and (3) diversification of cropping system using economically, environmentally and socially adapted crop rotation including legume crops and cover crops coupled with other complementary agronomic management practices (FAO, 2014).

9.1 Introduction

Water is essential for all life and used in many different ways. It is an important part of the ecosystem in which the reproduction of the bio diversity also depends. Fresh water scarcity for agriculture, industry and household purpose is not only limited to the arid climatic regions, but also in areas having high rainfall. Water scarcity is caused by low water storage capacity, low infiltration rate, high evaporation demand and larger inter annual and annual fluctuations of precipitation.

1 Brassica oleracea L. var. botrytis is the botanical name of

 a) Cabbage c) Cauliflower

 b) Knol-Khol d) None of these

 2 Cauliflower was introduced in India in 1822 by ________ from Garden, London.

 a) Dr. Jemson b) Dr. Kalloo

 c) Herbalist Dodens d) None of these

1 Which soil is most suitable for bottle gourd cultivation?

 a) Sandy loam soils. b) Clayey soil

 c) Clayey loam soil d) Silt loam soil

 2 The ideal pHof soil for growing bottle gourdis?

 a) 4-5 b) 8-9

 c) 3-4 d) 6-7

 3 What is the desirable soil temperature for good bottle gourd growth?

 a) 35-40°C b) 10-15°C

 c) 18°-22°C d) 40-45°C

1. What is the main negative impact of physiological disorders on root crops?

a) Deterioration of quality and visual characteristics

 b) Nutritional imbalance

 c) Decrease in yield

 d) None of these

2. Forking is a common physiological disorder of which root crop?

a) Radish

c) Beetroot

b) Carrot

 d) Turnip

1 What is the best time to sow onion seeds in Northern Hilly regions?

 a) January to February b)  March to April

 c) May to June  d) September to November

 2 Which type of soil is best for onion cultivation?

 a) Sandy loam    b)  Clay loam

 c) Alluvial soil  d) Both a and b

 3 What should be the pH range for onion cultivation?

 a) 4.4-5.0    b)  5.5-6.5

 c) 6.0-7.5    d)  6.5-7.5

1. The soils best suited for leafy vegetables are:

a) Clayey soils

c) Sandy soils

b) Well drained loamy soils

 d) Any type of soil 

2. How long does itgenerally take for leafy vegetables to grow?

a) 35-50 days after sowing

 b) 100-120 days after sowing  

c) 90-95 days after sowing

 d) 50-60 days after sowing   

1 The best age for transplanting of brinjal seedlings is: 

 a) 4-5 weeksold b) 1-2 weeksold

 c) 8-9 weeksold d) 10-12 weeksold

2 The recommended seed rate of tomato is: 

 a) 100-200g/ha   b) 1-1.2 kg/ha 

 c) 500-600g/ha   d) 33-4 kg/ha 

3 The best time for sowing tomato is: 

 a) September to October b) Mid-March to April 

 c )  Mid-December to January d) August to September  

1 Chromosome number of garden pea is 

 a) 2n=2x=14 a) 2n=2x=18

 c) 2n=2x=20 b) 2n=2x=22

2 Origin of French Bean  

 a) South America b) South Mexica

 c) Africa d) Europe

3 Pea is the  

 a) Cross-pollinated b) Often-cross pollinated

 c) Self-pollinated d) None of the above  

1. Quantitative characters are governed by

a) Monogene

c) Recessive gene

b) Bi-gene

 d) Polygene

2. Monohybrids are derived by hybridizing two individuals which differ for

a) Single-character

c) Quadruple character

b) Double character

 d) Multiple character

1 What is the isolation distance for raising foundation seed in bottle gourd? 

 a) 800 m b) 700 m

 c) 600 m d) 500 m

 2 Roguing of off-type plants in bottle gourd seed production should be done at how many stages?

 a) Three b) Four

 c) Two d) Five

 3 Where are bottle gourd seeds stored after extraction?

 a) Open containers b) Shade

 c) Air tight containers d) Open

1. Who is often referred to as the father of organic farming?

a) J.I. Rodale

c) Rudolf Steiner

b) Sir Albert Howard

 d) Rachel Carson

2. Which organization is responsible for setting and regulating organic farming standards in the United States?

a) United Nations (UN)

 b) World Health Organization (WHO)

 c) United States Department of Agriculture (USDa)

 d) Environmental Protection Agency (EPA)

1. Which type of vegetable is often grown in shade net house?

a) Tomato

c) Radish

b) Lettuce

 d) Cucumber

2. What is the primary advantage of greenhouse cultivation for vegetable production?

a) Increased exposure to natural elements

 b) Protection from pests and diseases

 c) Lower cost of production

 d) Reduced need for irrigation

1 Sechium eduleis the botanical name of

 a) Chekurmanis b) Basella

 c) Chow-Chow d) Water Leaf

 2 Cylon Spinach is also known as

 a) Chayote b) Malabar Spinach

 c) Indian Spinach d) Water Leaf

 3 Botanical name of Leek is

 a) Allium porum b) Allium sativum

 c) Allium cepa d) None of thes

1. Choose the correct option for the characteristic of growth.

 a) It is an irreversible permanent increase in size of an organ or its parts or

even of an individual cell

 b)  It is accompanied by metabolic processes

 c) It occurs at the expense of energy

 d)  All of the above

2. Plant growth is unique because

 a) Plants bear the capacity for unlimited growth

 b)  Plants bear the capacity for limited growth

 c) Plants have diffused growth that differs from animals

 d)  None of the above  

1 What is the scientific name of Dill

 a) Acorus calamus b) Pimenta dioca

 c) Pimpinella anisum d) Anethum graveolens

 2 Important chemical content present in Asafoetida is

 a) Phenol b) Terbein

 c) Ferumine d) Limone

 3 Karimunda is a variety of

 a) Ginger b) Black Pepper

 c) Cardemom d) Cumin

The term “fish” is usually a convenient description for a group of cold-blooded, ectothermic, aquatic non-tetrapod craniates that breathe with gills (Nelson, 2006). Fishes exploit every nook and niche of the domain of water. They are especially noted for their unimaginable numbers and bewildering forms. Most of them have a stream-lined body covered by scales and pose fins supported by fin rays and breathed by gills throughout life. They constitute the first group of animals that have developed biting jaws in the phylogenetic history of vertebrates.

2.1 Introduction

Life exists in almost all diverse habitats, ranging from high mountain peaks of more than 20,000 feet to deep sea bottoms of up to 10,000m. Living organisms can be found in ponds, pools, ditches, sulphur springs, hot springs, the cold of the Polar Regions, the scorching heat of deserts, dense tropical forests, and anywhere else life is possible.

However, not all organisms occupy all possible life-supporting areas.

3.1 Introduction

Fish are the only true aquatic vertebrates. These exploit every nook and cranny of the water domain. They are notable for their vast numbers and perplexing forms. In the phylogenetic history of vertebrates, this is the first group of animals to develop biting jaws. The origin, evolution and interrelationships of fishes are not fully understood due to incomplete fossil records and a scarcity of primitive types. The early appearance of bone, cartilage and enamel-like substances was crucial in the evolution of fish.

While describing fish, we need complete general information about the different specimens of fish included in the particular class or grade. A flow sheet of the general characters used in this concern may be tabulated as:

1. Origin of the term: The term Pisces comes from the old version of the plural of the Latin word piscis or singular word piscus meaning “fish.”

2. Literal meaning and definition: It describes either the creature or the meat from the creature. It is a streamlined, cold-blooded aquatic vertebrate with scales and gills,

3. Origin and evolution: The first fish appeared around 530 million years ago during the Cambrian period and then underwent a long period of evolution so that, today, they are by far the most diverse group of vertebrates. The Devonian Period is known as the “Age of Fishes”.

The term “fish” most commonly refers to Agnatha (jawless fishes), Chondrichthyes (sharks and rays), Sarcopterygii (lobe-finned fishes) and Actinopterygii (ray f inned fishes). Although the ichthyologist Regan (1910) defined a fish species as a product of interrelated communities with common “morphospecies”, in the early 20th century, it should be emphasized that the concept of species classification varied across scientists.

Aristotle (335-332 BC) provided the earliest classification of fish and described 117 Mediterranean fish species obtained from the Aegean Sea close to Greece.

Agnatha consists of cyclostomes, conodonts and ostracoderms. Among recent animals, cyclostomes are sister to all jawed vertebrates known as gnathostomes. They have little economic importance. It includes the oldest known craniate fossils and has many primitive characteristics.

The oldest fossil of agnathans appeared in the Cambrian period and two groups the lampreys (Hyperoartii) and the hagfish (Myxini or Hyperotreti) comprising about 120 species still survive today (Fig. 6.1).

Hagfishes are considered members of the subphylum Vertebrata, because they secondarily lost vertebrae; before this event was inferred from molecular and developmental data, the group Craniata was created by Linnaeus to reference hagfish and vertebrates.

7.1 Introduction

Placoderms (plate-skinned fishes) (Fig. 7.1) flourished and evolved in divergent lines during the Devonian period and became extinct by the end of the Permian period. They were bottom-dwelling, mud-sucking Palaeozoic fishes that may have been nectonic. Their bodies were divided into three parts: the head, the trunk and the tail. They ranged in size from 10 cm to 9 meters. The head and trunk are surely covered by bony plates.

8.1 Introduction

Cartilaginous fishes have ventrally placed mouths with teeth in several series. They possess rigid dorsal fins and placoid scales. They have five pairs of gill clefts opening individually to the exterior, a lower jaw articulated with the upper jaw and upper jaw not fused to the skull, no swim bladder, an operculum, an endolymphatic duct and a heterocercal or homocercal tail. It shows internal fertilization, meroblastic cleavage and direct development.

Elasmobranchii includes a wide range of cartilaginous fishes. Dogfish sharks are commonly studied all over the world probably because of their suitable size for dissection.

9.1 Introduction

Holocephalians are a group of highly specialised cartilaginous fishes that live in the sea. It is structurally similar to Elasmobranchii and Teleostomi. It exists in both extinct and living forms. Previously considered a class of Pisces, Nelson (1984) classified Holocephali as a sub-class.

9.2 Systematic Position

Phylum: Chordata

10.1 Introduction

Bony fishes (perfect mouth fishes) have a distinct mechanism for opening their mouths by lowering the mandible through the hyoid apparatus, skull either hyostylic or amphistylic. They have a single pair of respiratory openings, a movable maxilla and premaxilla, four-gill arches, a swim bladder, an operculum and a homocercal tail. They are both freshwater and marine. They vary greatly in shape but are built on the same basic plan.

11.1 Introduction

The crossopterygians, primitive, lobe-finned, bony fishes, represent a very interesting group of fish showing many features of amphibians and other tetrapods. They possess paired fins with a large median lobe, fins covered by scales, a cosmine layer, swim bladder as lungs, nostrils that open into the mouth cavity and autostylic jaw suspension.

11.2 Taxonomic position