Definition o weeds
1. Weeds are plants which interfere with the use of land for cultivation purpose. Weeds compete with crop plants for nutrient, soil moisture, sunlight and space.
2. A plant out of place or an undesirable plant with a negative value
3. A plant, usually herbaceous, which is growing in an area where it is neither desired not appreciated.
4. A plant growing where it is not desired
Characteristics of weeds
1. A concept of growing undesirable location
2. Competitive & aggressive value
3. Of wide & rank growth
4. Persistence & resistance to control or eradication
5. Consisting often large population with abundant rank & extensive growth
6. Useless, unwanted & undesirable
7. Harmful to men, animals, and crops
8. Spontaneous growth appearing without being shown or cultivated
9. High reproductive capacity
10. Unsightly with disfigurement of the land escape
11. Long duration seed dormancy
12. Wide range germination adaptability
13. Weeds can grow & survive field adverse condition
14. Legume weeds can grow accidently in nitrogen deficient soil
15. Resistance to insects & diseases
Special Characteristics of weeds
1. Weeds can produce numerous seeds
2. Ability to survive in adverse condition
3. Ability to propagate vegetitively
4. Ability to spread vegetitively
5. Persistent to chemical
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Classification of weeds
According to based of life cycle
1. Annual weeds
a. Rabi annual
b. Kharif annual
2. Biennial
3. Perennial
a. Simple
b. Bulbous
c. Creeping
According to cotyledons
1. Graminae
2. Cyperaceae
3. Araceae
According to nature of stem
1. Herbaceous –most of the weeds
2. Semi woody-lantana camera
3. Woody-acasia sp
According to economic utility
1. Absolute weed-all weeds
2. Relative weed – aus rice in jute field
According to ecology
1. 
Hydrophytic weed – floating
2. Mesophytic weed suspended
3. 
Zerophytic weed anchored submerged hydrophyte
4. 
Halophytic weed anchored hydrophytes with floating leave
According to leaf size
1. Narrow leaf weeds-graminae
2. Broad leaf weeds-
According to nature of damage
1. General weeds
2. Noxious weeds
a. -undesirable
b. -very difficult to control
According to site of predominance
1. Facultative weeds
2. Obligate weeds
According to association
1. Season bound
2. Crop bound
3. Crop associated
According to origin
1. Alien weeds
2. Apophytes
3. Antrophytes
According to taxonomic
1. Graminae
2. Cyperaceae
3. Leguminoceae
4. Compositae
Example of green fodder
1. k¨vgv
2. Chapra
3. Mutha
4. Durba
5. Av½yjx Nvm
Example of vegetative
1. Bathua
2. Shaknotey
3. gvjl&T
4. Nunia
Example of medicinal value
1. ‡k¦Z `ªb
2. wkqvj KvUv~
3. Mutha
Annual
1. Bathua
2. Chapra
3. k¨vgv
4. N¨vgv
Perennial
1. gy_v
2. `yev©
3. KPzwi cvbx
4. KvKv
5. Djy
Harmful effect of weeds
1. They compete successfully with crop for light
2. They compete successfully with crop for water
3. They compete successfully with crop for space
4. They compete successfully with crop for nutrients
5. They increase grow pest
6. They interfere with crop culture
7. They reduces crop quality
8. They also harms human health
9. They harms animal health
10. Some weed has allelopathic on crop
11. Weed contaminates water body
12. Weed interfere in non crop land
13. It increases production cost
14. It decreases crop yield
15. It decreases land value
16. It decreases agricultural product
17. It inspire the purity of variety
18. Cause health hazards both animal & man
19. Detracts form the beauty of public place
20. It causes accident
21. It causes pollution
22. Restrict the movement of water flow
23. Restrict drainage
24. Choke the
25. Increase wastage of water
26. Interfere in pisiculture
27. Impair cultivation of aquatic crop
28. Impair recreation in water bodies
Beneficial of weeds
1. Weeds help in controlling erosion by the soil bonding effects of their roots
2. Some weeds are used as green fodder
3. Some weeds are used as vegetable
4. Some weeds have medicinal value
5. Some weeds are used as thatch
6. Some weeds are used as organic matter in land
7. Some weeds are used as mulch
8. Some weeds are used as green manuring crop
9. Certain weeds are used as breeding purpose some weeds fixed atmospheric N2 in soil
10. Some weeds are used for beautification of lawn playground
11. Some dried weeds are used as fuel
12. Weeds are used as preparing for pup
13. Some weeds are used air population indication
Weed biology
1. Scientific study of living organism is called biology
2. Weed biology- Scientific study of formation of weeds and their different parts
Environment-
The natural conditions such as air water and land in which people animals and plant live
Weed biology
Is related to the study of weeds in relation to their geography distribution habit growth & population dynamics of weed species & communities. Development of an appropriate & effective weed management program, knowledge of weed biology is important. Effective management program of weed is dependent on sound knowledge of weed biology.
Weed biology include the following aspects
1. Weed classification
2. Weed propagation
3. Weed seed bank
4. Diversity weeds
5. Weed parasitism
6. Arelopathy of weeds
7. Weed ecology
Ecology
1. The scientific study of pattern of relation of plants animals and people to each other and to their surrounding
2. The study of relationship between living organisms & their environment
Weed ecology
Weed ecology study of relation of weeds with each other and their environment. All things that make up the environment are interrelated. Environment include climatic, edaphic & biotic. Factors & determines the distribution prevalence competing & behavior & survival of weeds. Man plays an important role in changing environment by altering the crop husbandary practice and maintaining weed free monocrop or multi crop culture
Persistence & dispersal of weeds
Persist
1. To continue to exist
2. Appear for a longer time
3. Is ability to with stand extreme of climatic, edaphic & biotic stresses of nature
4. is a measure of adaptic potential of a weed that enables it to grow any environment
5. Weeds are self-sown plants whereas crops are required to be planted by man with great care each year
6. is largely influence by climatic edaphic & biotic factors which affects its occurrence abundance range & distribution
Climatic factor
a. Light
b. Water
c. Wind
d. Temperature
Dispersal
Movement of seeds & other plant propagules to short or long distance away from the mother plant
Propagation
Reproduction of a new plant from an existing on either sexually by seeds or asexually by vegetative propagules
Propagules
Any individual unit of reproduction seed or other vegetative part
a. Rhizomes & root socks
b. Runners
c. Suckers & offsets
d. Tubers
e. Bulbs
f. Stems & roots
g. Bulbils
| Common name | Propagules |
| Durba | Rhizome stolone, seeds |
| Purple nutsadge | Tuber, bulb & seeds |
| Ulu | Rhizome, seed |
| Field bind weed | Creeping roots |
| Wild onion | Bulb, bulbil |
| Leafly sperge | Creeping roots |
| Thauni | Runner |
| Spurge | Runner |
| Water hyacinth | Runner |
Propagation of weeds
1. Seed
2. Vegetative organism
*******Available information from sheath
Dispersal
1. Wind
2. Water
3. Animal & man
4. Implements
5. Manures, comport
6. Farm machineries
7. Crop seed
8. Soil
9. Vegetative organ
Causes of persistence
1. Prolific seed production
2. Dormancy of seed- long duration seed dormancy & other vegetative propagules
3. To vegetative propagated –most weed propagate vegetatively
4. Rapid distribution
| Crops | Seeds /plants |
| Katanotey | 196000-200000 |
| Shaknotey | 196000-200000 |
| Bathua | 72000 |
| Nunia | 193000 |
| Chapra | 41200 |
| Mutha | 40 |
| Durba | 170 |
Crop weed competition
Competition
Latin word competere means ask or see. See means to make a legal claim. Test of strength skill or ability
Competition
The tendency of the plant of the same or different species growing together to strive for & capture the common resources. Such as light, water, nutrients and space of the habitat.
Inter- (between or among)
The competition amongst individuals of the same species is termed as inter specific competition E.g. crop weed competition
Intra – (within)
The competition amongst individuals of the some species is termed as intra Specific competitions. E.g. intra & intra row competition
Crop weed competition
1. Weed competition with crops is a part of ecology. Competition in ecology involves two or more organism seeking for a particular factor, thing or materials when they are in short or limited supply
2. The total effect of the competition as reflected in the crop growth & yield results from competition for nutrients moisture & sunlight
3. If weed emerge after the crop is established they may not pose as serious problem as these that emerge before the crop plant emerge & established
4. Competition between plants is maximum when available resources for crop growth become limiting
5. Competition between crop & weeds most severe when the competing plants have similar vegetative habit & demands for resources
6. The degree of weed competition is determined by the weed species, infesting area, densely of infestation & duration of infestation
| Crop | Weed | Soil fertility | |
| High | Low | ||
| Rice | Monochoria vaginalis | 64.6% | 58% |
| Echinochloa crusgali | 88.8% | 81% | |
| Crops | Weed | Soil fertility |
| Soybean | Cyperus rotandus | 58% |
| Groundnut | 32% | |
| Black gram | 23% | |
| Cow pea | 16% | |
| Green gram | 23% |
Competition for mineral nutrients
| Weed | % of nutrient | Nutrients |
| Amaranthus | Up -3 | N2 |
| Digitoria sanguinalis | Up-3.36 | P2o2 |
| Portulaca sp | Up-4.57 | K2o |
| Setaria sp | Up-585 ppm | Zn |
Competition for water
1. Chenopodium album -550 mm
2. Wheat -470 mm
Critical period of crop weed competition
1. Critical period of crop weed can be defined as that shortest life span in the life cycle of crop growth when weeding will measures result in highest economic returns
2. The crop yield level obtained by weeding during this short span should provide crop yield sufficiently close to that obtained by the full crop season freedom from weeds
3. The period of a life cycle of a crop in which it can tolerate weed competition with retain adverse effects of its yield & if weed is allowed to grow farther than significant reduction in yield occurs this period is called critical period of weed competition
| Crops | Yield losses due weed competition |
| Rice | 9-51 |
| Wheat | 6-35 |
| Maize | 29-74 |
| Sugarcane | 14-72 |
| Cotton | 21-61 |
| Peas | 25-35 |
| Miliets | 6-82 |
| Linseed | 31-39 |
| Ground nut | 30-35 |
| Carrot | 70-78 |
Factor affecting crop weed competition
1. Weed species
2. Weed density
3. Growth pattern of weeds
4. Duration of competition
5. Crop species
6. Crop variety
7. Planting date
8. Seed rate spacing
9. Planting pattern
10. Duration of crop
11. Climatic factor- light, temperature, moisture
12. Soil factors-soil-moisture, ph, organic matter texture
13. Tillage
14. Pests
15. Cropping practice-irrigation, applied fertilizer
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Allopathic effects of weeds on crops
Allelopathy
Is derive from the greek words allelo means each other & patho means an expression of sufferance of disease
1. The phenomenon of one plant having detrimental effect on another through the production are release toxic chemical
2. Allelopathy is defined as any direct or indirect harmful effect by one plant or another through production of chemical compound that escape into the environment leads to depletion of some essential factors like water mineral food & light
Allelo chemicals
Active chemical responsible for Allelopathic effects. They are the secondary metabolites in plant metabolism, chemicals with allelopathic potentials very from simple molecules .Such as ammonia to complex conjugated flavonoids. Most of the allele chemicals are derived from .Such diverse chemical groups as organic acids, aldihyds, aromatic acids, terpenoids & steroids, long chain fatty acids, alcohol, polypeptide, nucleosides
Secondary metabolites:
Substances that are produced by plant & are not directly involved with the main physiological pathways required for metabolism
Production of allelochemicals
Plants produce numerous chemicals during their growth and development. These compounds are released from plants as vapor as litching from the foliage, as exudates from the roots or in the course of brake down or any plant organs with roots, seeds & leaves being the most common sources. Flower & fruits may also produce allelopathic chemicals but these are less value in terms of allelopathic effect
Allelochamicals enter into the environment through volatilization foliage litching or root exudation .They may also result from the decomposition of plant residues’ great quantities of allelochemical are produce under condition of mineral deficiency, drought stretch & cool temperature then at the more optimum growing conditions
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Effect of allelochemicals on plants
1. It increases weed seed longitivity
2. It habits germination & seedling establishment
3. They inhabit growth of the desire plant
4. It interferes with uptake of nutrients particularly N & K by maize
5. It caused reduction in yield ranged from 40-100
6. It inhabit nodulation in legumes
| Crops | |
| Cynodon dactylon | Inhabit seed germination, root & top growth barley, maize etc |
| Cyperus esculentus | Inhabit germination of oat & other crops |
| Cyperus rotundus | It reduces the crop yield ranging from (23-89) rice yield 38% |
| Echinochioa crusgalli | It reduces crop yield ranged from (19-79) |
| Amaranthus retroflexus Digitaria sanguinalis Portulaca oleracea Canopedium album | Inhabit germination of cabbage, carrot, radish, peeper, tomato, turnip |
| Setaria faberi | Reduces maize yield |
| Imperata cylindrical | Inhabit emergence & growth of annual weeds & crops |
Weed management
Weed management:
The rational developments of appropriate technology to minimize the impact of weeds provide systematic management of weed problem & optimize intended land use
Management:
The art or practice of managing specially of managing a business or money
Principles:
The general rules on which a skill since etc. is based & which be gainer understand
Weed prevention
Stopping weed from invading & contaminating new areas
Weed eradication
A complete elimination of all life plants parts & weed seeds from an area
Weed control
1. The process of limiting with infestation so that crops can be grown profitably or other operations can be conducted efficiently
2. The process of reducing weed crop or weed infestation to & acceptable grown
Weed prevention
Preventing weed control encompasses all measures taken to prevent or arrest introduction & spread of weeds
Quarantine
Control of import & export of plants or parts of plants to prevent spread of disease & pests
The important weed prevention recommendations are as follows-
1. Avoid using crop seeds that are infested weed seeds for sowing
2. Avoid adding weeds to manure pits
3. Avoid livestock fields, containing weed seeds
4. Use clean form machinery in the field
5. Avoid the use of gravel sand & soil from with infested area
6. Keep irrigation channels, fence, and lies uncropped area clean
7. Use vigilance
8. Using well decomposed weed free farmyard manure & compost
9. Seed certification- helps in supplying genetically pure seeds & propagating materials
10. Seed laws
11. Quarantine law- restrict the entry & inter state or international movement of imported plants capable of speeding plant disease and insects
Cultural method of weed control
Crop husbandry
The practice of growing and harvesting of crop
Weed control
1. Proper crop stand and early seedling vigor
2. Selective crop stimulation
3. Proper planting method
4. Proper planting time
5. Crop rotation
6. Stole seedbed
7. Smother cropping
8. Summer fallowing
9. Minimum tillage
10. Lowering areas drainage
Chemical method of weed control
Herbicide comes from Latin word Habra plant caedere (to kill) 1896 discovered Bordeaux mixture.1896-1910(U.S.A and Germany).Martin & bornet in france , Bolley in USA, Schults in Germany
rescarchers who contributed to the chemical weed control during the period 1896 to 1890
Over 400 herbicides have been developed & already registered to the world market for chemically weed control currently herbicide constitute 55% of the world pesticides markets
Chemical weed control:
Application of herbicide to crop for bare land to kill weeds chemical weed control played a significant role in the develop countries.
Advantages of chemical method of weed control=
1. Herbicide can control weeds before emergence of crop seedling so that crop can germinate and grow in completely weed free environment .this is usually not possible with physical method.
2. Weeds can be controlled irrespective of season.
3. It kills all weeds in the field.
4. Intra row weed control is possible.
5. Control last longer.
6. It can control spiny weed.
7. It presents soil erosion.
8. It reduces production cost.
9. It is very effective for controlling perennial weed.
10. It increases crop yields.
11. It reduces processing cost.
12. It requires less time labor and money.
Disadvantages of chemical method
1. It requires special technical knowledge about crop herbicide weed soil & environment
2. It requires special prequations before application
3. It may affect the physical, chemical & biological properties of soil
4. It creates unemployment of labors
5. It hampers other intercultural operation
6. It requires the availability of herbicides in the market
7. It requires implements for application of herbicides
8. Very high & low doses are not effective
Causes of introducing herbicides in agriculture
1. To replace torturous & back breaking manual weeding
2. To give leisure to the farmers
3. To spread labor comb be utilized efficiently for bringing additional land under cultivation for improving irrigation, fertilizer & other pesticides application practices
4. Swelling costs of hired labor & limited supply of fuel to fill the land for weed controls are to other reasons for introducing herbicides in Agriculture
5. The herbicides are not aimed at substituting the physical biological or good crop husbandry methods of weed control. They are meant to bridge the gaps in these methods & act as added tools in agriculture practical weed control is a combined effect of good crop husbandry herbicides & other methods. Proper crop husbandry practices weaken weed population which then succumb to the herbicides at low doses
Scope of wing herbicides in agriculture
Herbicides have ample scope in -
1. Vegetation management both on crop lands & non crop lands including water bodies
2. To destroy established weeds in croplands
3. Herbicide can be employed to main weed sanitation
4. Herbicides are useful tools in suppressing unwanted vegetation in industrial areas, roadsides, along the rail, other homestead & farmstead area
5. In summery where there is need to manage vegetation efficiently there is scope of wing herbicides
Bioagent
A living organism employed to control a pest
Biological control of weeds
1. Biological control of weed involves the use of living organisms such as insects, herbivorous fish & other animal’s disease organisms & competitive plants, to limit weed infestation
Classical biological weed control aims at restoring the balance between the target weed and its natural enemies in ecosystem by purposeful introduction of the exotic bioagents
Kinds of bioagents
1. Insects 4. Mites
2. Carp fish 5. fungi
3. Snails 6. Competitive plant
| Name of bioagents | Name of weed controlled |
| Insect- crocidoseca lantana | Lantana camera |
| Carp fish-common carp | Noxious aquatic weeds |
| Snail- marisa cornuarietis | Submerged aquatic weeds |
| Mite –tetranychus desertorum | Prickly pears |
| Fungi –puccinia chondrillina | Chondrilla juncea |
| Competitive plant –panicum purpurascans | Typha sp |
Criteria of a successful bioagents
1. Host specific
2. Adjustable to the new environment
3. Rapid feeder of the target weed
4. Early to multiply
5. Effective on several texa of weed in question
Advantages of bioagents
1. No adverse effect on environment
2. Suitable for non crop area
3. It is applicable to the control of a single major weed species
4.
Disadvantages
1. Not suitable for crop area
2. Method being a slow operating area
3. Selection of bioagent in very difficult
4. Environment factor is a major problem
5. Did not fulfill the target weed
6. Sometime harmful to beneficial plants or other crops
7. Some bioagents are suitable for aquatic weeds only
Integrated weed management
Type
1. Selective herbicides
2. Non Selective herbicides
IWM:
1. Use more than one method instead of one is called integrated weed management
2. Application of many kinds of weed management technique in a mutually supportive manner
According to FAO-
1. The integrated campaign against pests is a method hereby all economically, ecologically and toxicologically justificial method are employed to keep the harmful organism below the threshold field level of economic damage also called system
2. Also called system approach the integrated weed management involved development of different method of weed prevention & control in proportion & at appropriate time against the target weeds without damaging the environment in any way, in fact IWM program should be strongly on plant community & ecological behavior of weeds
3. Among the weed control methods, namely chemical biological mechanical, physical & good crop husbandry methods, no one method is superior to the under others under all situation to much reliance one any one method of control at the excular on the other method will not be successful & economical. For this reason we can apply on this method at a desirable level for get maximum effect
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Principles of integrated weed management
To the method used for weed control must be selected to the following aspect
1. A through knowledge on weed characteristics their response to different environmental condition & their adoption to different habitat are essential.
2. Before selecting the method of weed control one must have information one number of viable seeds produced nature of dispersal of seeds, dormancy of seeds, longevity of buried seed & ability to survive under adverse condition
3. They life span of weed is another aspect of importance of selecting the weed control method
4. Soil texture & structure & moister are important factors one has to be taken into account in electing method of weed control
5. Depending on the habitat & location of weed, it is important to consider when the a particular method may not have & adverse residual effect on soil fertility
6. There are to be control has to be taken into account in selecting the method of weed control
Weed management
Weed management may be defined as the rational development of appropriate technology to minimize the impact of weeds provides a systematic management of weed problems & optimum land use
Basic principles of integrated weed management
1. Suppression of weed growth
2. Prevention or suppression with seed production
3. Reduction of weed seed reserve in the soil
4. Prevention or reduction of weed spread
***IWM explores the possibility of employee biological, ecological & cultural method of weed management
**weed scientist need to study the consequences of herbicides on soil crop yield, environment, and ecology
The modern weed scientist is required to gain adequate knowledge in agronomic, soil genetically, biological, physiological, biochemical, environmental, doxological & economic aspects of plant growth, behavior & production & utilize it to eve love a package of integrated weed management strategies comprising chemical, biological cultural mechanical & minimum method
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Herbicides
1. Herbicides are chemicals which are used for killing weeds
2. Herbicides are chemicals, used for inhibit the growth of weeds
3. Herbicides are chemicals which are used for the limiting growth of weeds
4. Herbicides are chemicals which are used for remaining the growth of weeds
Scope
1. Food production increased
2. To bring more land under cultivation
3. Intensification of cropping
4. Introduction of modern varieties
5. Seed production
6. Lack of labor in the agricultural field
7. Higher wages rate
8. Less efficiency
9. Commercial production of seed, vegetable, fruits
10. Agricultural labor are employed in different sector
Classification of herbicides
A.
1. Selective herbicides
Selective herbicides are those which affect only certain weeds, leaving, and certain crops unharmed like pre-emergence application of atrazine in maize crop. The selective herbicides are used in agricultural and horticultural fields. E.g. 2, 4-D, alachlor, atrazive etc are selective herbicides used in mixed population. That kills certain weeds only
2. Non selective herbicides
A non selective herbicide, on the other hand, is one that kills all plants without regard to species. E.g.paraquat. Sodium chlorate, acrolein- they are used to control wide range vegetation indiscriminately
Because they are toxic to all plants and higher susceptible to living plants tissues. These are for non selective use on waste land, rail tracts, road sides, industrial sites and aquatic weed control. That kills all vegetation
B.
1. Narrow spectrum herbicides
It proves active on one or a very limited number of plant species. Most of other plants remain tolerant to such herbicides. It is very useful against specific noxious weeds. The wild Avian and pohalaris spp killing herbicides matoxuron, difenzaquat and diclotop ane very successful examples of narrow spectrum herbicide
2. Broad spectrum herbicides on the other hand, central a wide- spectrum of weed flora. Most of the herbicides used belong the group e.g. paraquat , diquat etc.
C.
1. Soil active herbicide:
A soil active herbicide is one that is applied primarily to the soil rather than to the vegetation. Inside soil at kills weeds as they germinate or inhibits sprouting of their rhizomes, stolons, and tubes. Therefore, in crop field, a soil active herbicides eliminates early crop weed competition for the period at remain active is active. This period is usually 6-8 weeks .depending upon the herbicide and its role used. The soil active herbicides are largrely applied at the time of planting of crops. E.g. Simazine, alachlor, trifluralin and EPTC on non cropped area. The soil active herbicides are used sterilants and fumigants
2. Foliage active herbicides
Foliage active herbicides are applied to weeds after their emergence from soil. They are absorbed by plant foliage and in many loses then their are translocated to other plant parts. They are effective against young weeds in their seedling stages, e.g. paraquat diquat. Amitrole. There may be some herbicides that are both soil and foliage active e.g. 2, 4-D picloram and atrazine
D.
1. Contact herbicides. (mode of action)
A contact herbicide kills plant primarily by contact with plant tissue rather than as a result of translocation. Thus a contact herbicide applied to the foliage of a plant will not well its roots. They are toxic to living cells rail as phloem. E.g. alachlor, butachlor propanil, nitrofen paraquat(kill plant tussues at or very close to the site of application
2. Traslocted herbicides
These are systemic herbicides which are readily absorbed by either the roots (in case of soil application) or above ground parts and are translocation through the plant system and thus …. Effective, even in hilling the roots of perennial weed e.g. 2,4-d MCPA.(these herbicides move within the herb or weed .they may gain entrance into the palnts through their live and or the roots and from these organs move to the other parts of the weed.
Mode of action=the total plytotoxic effects & fate of a herbicide on or in a plant.
E.Method of application
1. Pre planting
2. Pre emergence
3. Post emergence
Pre planting or pre sowing application
=Herbicide is applied after land preparation &.before the crop is planted
e.g Fluchloralin ,Nitrofen
Pre-emergence application
=The herbicides are applied after the crop has been sown but before the emergence of the crop or the weeds. This method is adapted to destroy weeds in the earlier stages. It is only possible where a crop is slow in germination & weeds emergence rapidly. The weedicides suitable for pre emergence spraying are those which are either quickly inactivated on reaching the soil or in cases where the crop is tolerant to there action. (2, 4-D), alachlor simazine.
Post emergence application
=the herbicides are applied after the emergence of crop & the weeds. These types of spraying can largely be practiced with selective weeds killers. viz, weed killers which kill the weeds ,but do not harm the crop.2,4-D atrazine.
The time & method of chemical application dept on-
Type of weed
Type of crop
Soil condition
Soil environment fallen
Auxin type=Kill the plant by upsetting their Metabolic activities
Other regulators=destroy plants by actives systemic poisons.
Soil sterilant=these are herbicides that render (togive, to perform) the soil in capable of supporters' plant growth
Classification herbicide based on selectivity, mode of action
Selective
Careful in choosing, hang & effect only one certain thing not generate
Selectivity
The extend of tolerance of desired plant to the amount of herbicide needed to control specified weeds
Property of differential tolerance essential for the proper function of herbicide that kills some plant species when applied to a mixed population but without aurous damage to other species
Herbicide selectivity
Refers to the phenomenon where in chemical kills the target plant species in a mixed plant population without harming or slightly affecting the other plant
Herbicide activity is related to the phototoxic effects of a chemical on plant growth & development. An herbicide is saving to be active, or to causes activity it hinders, inhibits or prevents to germination plant growth processes of the plant. It is active one sensitive plant & inactive on tolerant or resistant Plant. Hence, herbicide activity is determined by the degree of tolerance of the plant to a chemical
Herbicide activity & selectivity are closely related. Activity refers to the ability of the herbicide to control a weed, while selectivity refers to its ability to control it without affecting the others in a mixed stand. Even though an herbicide exhibit activity it would affect either selective or non selective weed control
Factors affecting herbicide activity & selectivity
1. Plant morphology
2. Stage of plant development
3. Cultivation practices
4. Environmental factor
5. Herbicide absorption
6. Herbicide translocation
7. Physiological difference
8. Herbicide metabolism
Both activity & selectivity are dependent one a complex chain of events beginning from application to disruption of vital function of the plant. The chain is mediated mechanically, chemically & metabolically. The various factor that affect herbicide activity & selectivity are briefly discussed below
Plant morphology
It has a dominant role in determining herbicide activity & selectivity. The amount of spray retained to held in place by the following influences the amount of chemical available for entry into the plant the various morphological characteristic of the plant that affect herbicide entry are leaves size and shape leaf enlargement to pubescence waxinass of the leaf & thickness of the cuticle leaf area & degree of overlapping
Stage of plant development
Increase of annual weed herbicide is effective at germination early seedling stage while perennial weed herbicide is effective at fully developments stage
Cultivation practice:
Formulation of herbicides
Formula
A method or set of principles
Formulat:
To express in an exact way
Formulation herbicide
1. the process by which herbicidal compound bare prepared for practical use
2. A preparation containing a herbicide in a form practical use
Concentration
Amount of active ingredient express in percent
Immulsion
Suspension of one liquid as minor glucose globules in another liquid without losing is identity
Surfactant
A material which improves emulsifying dispersing spreading wetting properties of liquid
Suspension
Finely divided solid particle aspersed in a solid liquid or gas
Wetting agent
Substance which serves reduce interfacial tension & causes spray solution to make better contract with treated surfaces
Wetable popoder
A finely dinied dry herbicide formulation that can be suspended readily in the water
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Emulsifier
A chemical which facilitate the formulation of an emulsion. The material that facilitates suspensions of one liquid in another
Emulsifiable concentrate
A homogenous liquid formulation which farms & emulsion or mixing with water
The biological efficacy of herbicide depends to a large degree on the type of formulation it is made into formulation is the process by which the technical ingredient are made ready to be use by mixing with liquid & dry diluents by grinding & or by the addition of emulsifiers a stabilizers & formulation adjuvant. Formulation herbicides involves conversion of a technical active ingredient to a commercial product develop a formulation depends on the physiochemical properties of the active ingredient to be formulated & of the inner material to be used in the formulation
Active ingredient
Is that part of a formulated product that is principally responsible for herbicidal effects? An active ingredient may be a solid, liquid ion gas most technical ingredient can not be used for control of weeds without further processing into a suitable formulation. It is normally adventitious to make active ingredient as pure as possible
Herbicide formulations have mainly 3 components
1. The toxicant
2. Solvent
3. Adjuvant
Type of formulation
1. Wet able powder
2. Soluble powder
3. Emulsifiable concentrated
4. Soluble concentration
5. Granule
6. Fumigants
Adjuvant
1. To improve herbicide selectivity to the non target plant
2. To render herbicide safer for the users
3. To prolong shelfhfe of the conuntrote
4. To reduce hazards
5. To reduce drift hazards and for same other similar regions
Function of 8 kind adjuvant
1. Surfactant (surface acting agent
2. Stabilizing agent
3. Solvent
4. Humicants (hygroscopic agent) –prevent to rapid drying
5. Stickers
6. Activators
7. Compatibility
8. Drift control
Mode of actions of herbicides
Interference with photosynthetic process
1. Electron transport blackage
2. Electron transport deflection
3. Photophospharylation
Interference with normal respiration
1. Uncouplers of photophospharylation
2. Inhibition of glycolysis
Interference with plant growth
1. Mitotic poisons
2. Cell protifereation
3. Antigeotropism
Interference with biosynthesis reaction
1. Protein synthesis inhibition
2. Lipid synthesis inhibition lass of cell membrane permeability
3. Inhibition of carotenoate synthesis
Other actions
1. Inhibition of enzyme activity in seeds
2. Denaturation of plant protein
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Photophosphrylation
The synthesis of ATP in eliminated chloroplast
The various physiological & biochemical process affected by herbicides are grouped into the following categories. These are
1. Photosynthesis
2. Mitochondrial activities
3. Protein & nucleic acid biosynthesis
4. Pigments biosynthesis
5. Fatty acid biosynthesis
6. Pronched chain amino acid biosynthesis
7. Aromatic compound biosynthesis
8. Glutamine biosynthesis
9. Hydrolytic enzyme activities
10. Ethylene biosynthesis
Fate of herbicide
The dilution of the herbicide in the soil by its transfer for decomposition, there are two ways by which herbicide dissipate from the root zone of the soil
These are under
1. Transfer
2. Decomposition
Transfer herbicide
Division of herbicide into parts among different phases of the soil
1. A herbicide may be subjected irrersible adsorption on colloidal particle
2. Herbicides may gradually leach below root zone of crops & volatilization into the atmosphere
3. A herbicide may subjected to runoff losses, and /volatilization
4. The herbicide are invariably absorbed by the weeds & the crop plants
Chemical composition
A pathway of herbicide degradation in soil which may involve hydrolysis, oxidation, reduction, alkylation etc. the rate of degration is proportional to consideration. It is usually begins as soon as herbicide applied to the soil
Photode composition
Decomposition of toxicant molecule structure under the influence of light from a surface.
Degradation
Alteration of herbicide molecule structure in plant or soil leading to its inactivation
Herbicides are absorbed & metabolize by plans. A return to the soil. Either in the original form as metabolized through crop & weed residues. A portion of absorbed herbicide may be circulated through the plant & returned to the soil in & unchanged form by roots exudation or a par of herbicide absorbed by plant is retain in the ere able portion of the plant & the rest is return to the soil though crop residues
Factors affecting soil applied herbicide
1. Soil component –sand silt by, gases, microorganism, nutrient organic matter
2. Soil process-which determine herbicide availability to the weeds
3. Absorption on soil colloids –soil. Texture, soil moisture, organic matter, chemical nature of colloids
4. Photodecomposition
5. Chemical decomposition
Effect of herbicides on environment
1. Soil microorganism
2. Soil fertility
3. Human health hazards
4. Water pollution
5. Air pollution
6. Crop plant
| 2,4-D | 2,4 dichlorophenoxy aceric acid |
| MCPA | 4 chlaro- 2 methylphenoxy acetic acid |
| MCPB | 4 chlaro- 2 methylphenoxy butanoic acid |
| Dalapon | 2,2 dichloroprapanoic acid |
| Tca | Tri chloro acetic acid |
| Propanil | [ N-(3,4 dichlorophenul) propanomide] |
| Nitrofen | [2,4-dichloro-1-(4 nitrophenoxy) benzene] |
| Name of the herbicide | Conuntration(%) | Pate of application | Mode of treatment | Controlled weed |
| Alachlor | 48 Ec, 10g | 2-3 | Preemergence | Broad leaf grass |
| Atrazine | 50wp | .5-2 | Preemergence | Grass |
| Butachlor | 50 Ec,5g | 1-2 | Preemergence | Broad leaf grass |
| 2,4-D | 80sp | .5-2 | Postemergence | Broad leaf grass |
| Dalapon | 85 wp | 1.5-2 | Postemergence/ Preemergence | Grass |
| Diquat | 20Ec | .5-1.5 | Postemergence | Grass |
| Mcpa | 75 Wp | .25-2 | Postemergence | Broad leaf grass |
| MCPB | 40wp | .5-1.5 | Postemergence | Broad leaf grass |
| Nitritin | 15wp | 1-1.5 | Preemergence | Broad leaf grass |
| Nitrofen | 25 Ec | 2-5 | Preemergence/ Postemergence | Broad leaf grass |
| Paraquat | 10 Ec | .5-1 | Postemergence | Broad leaf grass |
| Propalin | 35 Ec | 1-2 | Postemergence | Broad leaf grass |
| Simazine | 50 wp 20g | 1-3 | Preemergence | Grass |
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| Sl no | Common name | English name | Scientific name |
| 1 | Durba | | Cynodon dactylon |
| 2 | Chapra | | Eleudine indica |
| 3 | Bara Anguli ghash | | Digitaria sanguinalis |
| 4 | Khudey Anguli ghash | | Digitaria ischaemum |
| 5 | Arail | | Leersia hexandra |
| 6 | Gaicha /monaghash | | Paspalum commersonii |
| 7 | Angta /gitla ghash | | Paspalum distichum |
| 8 | Bara Shama | | Echinochloa crus-galli |
| 9 | Khudey Shama | | Echinochloa colonum |
| 10 | Carpet ghash | | Axonopus compressus |
| 11 | Chela ghash | | Parapholis incurve |
| 12 | Prem kata | | Chrysopogon acciculatus |
| 13 | Halud Shial leja | | Setaria glauca |
| 14 | Shabuj Shial leja | | Setaria viridis |
| 15 | Kakpaya ghash | | Dactyloctenium aegyptium |
| 16 | Ulu | | Imparata cylindrica |
| 17 | Kash | | Saccaharum spontaneum |
| | | Cyperaceae | |
| 18 | Mutha / Bhadail | | Cyperus rotundus |
| 19 | Holde mutha | | Cyperus esculentus |
| 20 | Bara chucha | | Cyperus iria |
| 21 | Sbuj nakful | | Cyperus difformis |
| 22 | Shakta khagra/ uha | | Cyperus pilosus |
| 23 | Pani chaise | | Eleocharis atroperpurea |
| 24 | Joina | | Fimbristylis miliacea |
| 25 | Mati chaise | | Fimbristylis diphylla |
| 26 | Chechra | | Scirpus mucronatus |
| 27 | Mutha chaise | | Cyperus compressus |
| 28 | Khudey patai | | Cyperus flavidus |
Poaceae
Amaranthaceae
| 29 | Shaknotey | | Amaranthus viridis |
| 30 | Katanotey | | Amaranthus spinosus |
| 31 | Chanchi | | Alternanthera sessilis |
| 32 | Malancha | | Alternanthera philoxeroides |
Araceae
| 33 | Topapana | | Pistia stratiotes |
| 34 | Kachu | | Calocasia esculenta |
Azollaceae
| 35 | Khudipana | | Azolla pinnata |
| | | | |
Boraginaceae
| 36 | Hatisur | | Heliotropium indicum |
Campanlaceae
| 37 | Halud nakpul | | Wahlenbargia marginata |