Chapter 4 Weed Science PDF

CROP PROTECTION 1 (Weed Science) JOANNE A. LANGRES, MSc. Faculty, Crop Protection Division College of Agriculture and Agri- Industries Caraga State University Ampayon, Butuan City, Agusan del Norte, Ph  TOPIC OUTLINE 1.Weed Science...

CROP PROTECTION 1 (Weed Science) JOANNE A. LANGRES, MSc. Faculty, Crop Protection Division College of Agriculture and Agri- Industries Caraga State University Ampayon, Butuan City, Agusan del Norte, Ph  TOPIC OUTLINE 1.Weed Science (defined) and Concept of Weeds 2. Characteristics of Weeds 3. Weeds, Crops and Other Pests 4. Classification of Weeds 5. Effects of Weeds on Human Affairs 6.Reproduction and Establishment of Weeds 7. Crop-Weed Competition 8. Change in Weed Populations Weed Science (defined)  Weed Science (defined) Involves the development of knowledge in a variety of areas: weed biology taxonomy and ecology biological control cropping systems integrated management systems (applied weed control) conservation tillage transgenic crop tolerance Herbicides (Physiology and Chemistry) The development of knowledge of the major mechanisms of weed survival is essential for developing effective methods of weed management. Definition of Weeds Concept of Weeds According to Plant Scientists Author Year Definition Robinsons et al. 1942 These obnoxious plants are known as weeds Muenscher 1935 & Those plants with harmful or objectionable habits or 1955 characteristics which grow where they are not wanted, usually in places where it is desired that something else should grow Harper 1960 Higher plants which are nuisance King 1966 The more aggressive, troublesome and undesirable elements of the world’s vegetation. Salisbury 1961 A plant growing where we do not want it Klingman 1961 A plant growing where it is not desired; or a plant out of place Definition of Weeds Concept of Weeds According to Enthusiastic Amateurs Author Year Definition Emerson 1878 A plant whose virtues have not yet been discovered. King 1951 Weeds have always been condemned without a fair trial. Definition of Weeds Concept of Weeds According to Ecological Definitions Author Year Definition Bunting 1960 Weeds are pioneers of secondary succession, of which the weedy arable fields is a special case. Batchley 1912 a plant which contests with man for the possession of the soil Pritchard 1960 those species which grasp the opportunities offered frequently become serious weeds and, by following in the wake of human activities, rapidly expand their range of distribution. Definition of Weeds Concept of Weeds According to Ecological Definitions Author Year Definition Quammen 1998 They reproduce quickly, dispersed widely when given a chance, tolerate a fairly broad range of habitat conditions, take hold in strange places, succeed especially in disturbed ecosystems, and resist eradication once they’re established. They are scrappers, generalists, opportunists. They tend to thrive in human-dominated terrain because in crucial ways they resemble Homo sapiens: aggressive, versatile, prolific, and ready to travel. Salisbury 1961 “the cosmopolitan character of many weeds is perhaps a tribute both to the ubiquity of man’s modification of environmental conditions and his efficiency as an agent of dispersal.” Definition of Weeds Concept of Weeds Summary: a plant growing out of place a plant growing where it is not desired a plant that is useless, unwanted, and undesirable a plant that interferes with man or area of his interest a plant whose virtues have not yet been discovered a plant with negative value unwanted and undesirable plants which interfere with the utilization of the land and water resources, and thus affect human welfare All these definitions point to the fact the word “weed” has a negative connotation and its definition is based on how man perceives it. Concept of Weed is man made - he decide which plant is harmful and which is beneficial Lantana camara Peperomia pellucida - Definition of Weeds Concept of Weeds Man-made concept weeds interfere with human agricultural management or activity; plants that are unwanted, useless, increases cost of production, reduces crop yield and lower quality of products; and plants whose potentials for damage outweigh its potentials for usefulness. weeds include plants that are agrestals (enter agricultural land) and ruderals (occur in waste places as well as along roadsides) weeds may grow wild and in cultivated areas (Muzik, 1970)  Definition of Weeds Concept of Weeds Obligate weeds associated with man or found only in cultivated areas Facultative weeds found both in the wild state and in cultivated habitats Lantana camara Chromolaena odorata Noxious weeds/ Pesky found commonly in the field and are difficult to control Common weeds found commonly in the field and are easy to control Cleome rutidosperma Ageratum conizoides Definition of Weeds Concept of Weeds A plant species can behave as a weed depending on the situation. A crop and an ornamental can be a weed if these are growing in areas where they should not be. A crop plant that is out-of-place is called “volunteer” An ornamental plant that is out-of-place is called “escape” Unique and Distinct Characteristics Weed Characteristics 1 They have rapid vegetative growth and profuse root production Production of leaves, branches, off-shoots, modified storage structures and other vegetative parts is fast. They produce very extensive roots that are efficient in absorbing water and nutrients fromthe soil. 2 They reproduce early and efficiently Most weeds reach the reproductive stage earlier than the crop they are associated with. Perennials reproduce both through seeds and vegetative propagules, while annual weeds normally reproduce through seeds. Unique and Distinct Characteristics Weed Characteristics 3 They are adapted to competition and adverse environmental conditions Weeds have evolve through natural selection, enabling them to survive even under harsh environments. Through time, they have developed efficient mechanisms so that they can compete better than the crop for needed growth requirements. 4 Their seeds and vegetative propagules are usually dormant or can be induced to become dormant Because of this, the number of weed seeds in the soil cannot be depleted. Every time the soil is disturbed, a new set of weeds appear. Unique and Distinct Characteristics Weed Characteristics 5 They cause significant damage even at low population densities They are highly adapted to competition that even with only few individuals, they could reduce yield. 6 They persist and resist control measures Weedsare difficult to eradicate.They have mechanisms that enable them to survive in any environment and resist control measures.There are even weeds that are tolerant to weed control measures. Harmful Effects of Weeds Weed Characteristics 1 Reduce yield quantity and quality 2 Increase the cost of crop production or maintenance of an area 3 Act as alternate hosts for harmful insects, disease causing organisms and other pest 4 Impose hazards to human and animal health 5 Clog waterways and irrigation canals 6 Release harmful chemicals (allelopathy) that affect the growth of adjacent crops, including the crop of succeeding season Beneficial Effects of Weeds Weed Characteristics 1 Food for man and animals 2 Aesthetic value to beautify areas 3 Prevent/ minimize soil erosion in hilly areas 4 Source of possible medicines and pesticides 5 Source of genes for crop improvement 6 Return organic matter and nutrients into the soil after decomposition  Weed, Crops and other Pests Crops and weeds are both similar botanically and that they need water, nutrients and sunlight for their growth. The only difference is that crops are intentionally grown for food and other uses, while weeds grow unwantedly that they compete with our crop. At the same time, other pest such as disease causing pathogens, arthropods and vertebrate animals would rely to both our crops and weeds in terms of food and shelter for them to survive. Both pests and weeds are living organisms. They are also detrimental to the existence of other living organisms and mostly crops, livestock, and human beings. However, despite their striking similar characteristics, the two are different in various ways including their nature as well as existence. Classification based on: Weed Classification Origin Exotic (imported) Habitat Endemic (native) Lifespan Growth habit Naturalized/ Adventive – these are exotic weeds that need the Stem structure interference of man in order to grow Gross morphology in a new place Manner of reproduction Inflorescence/ Floral structure Classification based on: Weed Classification Origin Upland (terrestrial)/ Dryland weeds Habitat Lowland (aquatic)/ Wetland Lifespan weeds Growth habit Floating Stem structure Emerged Gross morphology Submerged Manner of reproduction Inflorescence/ Floral structure Classification based on: Weed Classification Origin Annual (1 year or less/ one growing Habitat season) Lifespan - seeds Growth habit Perennial (grow beyond one year) Stem structure - seeds and vegetative propagules Gross morphology Manner of reproduction Inflorescence/ Floral structure Classification based on: Weed Classification Erect (grow vertically; no support) Origin Creeping (grow horizontally) Procumbent – horizontal orientation of Habitat apex Decumbent – vertical orientation of the Lifespan apex Twining – seeking a host where it can Growth habit climb; vertical host Stem structure Gross morphology Manner of reproduction Inflorescence/ Floral structure Also known as prostrate type Classification based on: Weed Classification Herbaceous – stem is succulent, fleshy, soft Origin stem with high water content (1) Habitat Woody – stems that are rigid and hard Lifespan because of the presence of the bark (2) Growth habit Stem structure Gross morphology Manner of reproduction Inflorescence/ Floral structure (1) Peperomia pellucida (2) Lantana camara Classification based on: Weed Classification Gross morphology CATEGORY LEAVES STEM ROOTS Grass Narrow, elongated, parallel Rounded Fibrous veins, leaf sheath, leaf blade Sedge Narrow, elongated, parallel Triangular Fibrous veins, leaf sheath, leaf blade Broadleaves Wide, broad, netted veins Variable Generally tap rooted, some are fibrous Classification based on: Weed Classification Gross morphology Family Poaceae Family Cyperaceae Varied/ all families other than grasses and sedges Classification based on: Weed Classification Sexual – is one that reproduce through seeds Origin Habitat Asexual – is one that reproduce by means of vegetative propagules Lifespan Growth habit Stem structure Gross morphology Tubers of Cyperus rotundus Manner of reproduction Inflorescence/ Floral Rhizomesof Imperata cylindrica Suckers of Pistia stratiotes structure Stolons of Cynodon dactylon Classification based on: Weed Classification Origin Habitat Lifespan Growth habit Stem structure Gross morphology Panicle Digitate Raceme Umbel Manner of reproduction Inflorescence/ Floral structure World's Worst Weeds Major Weeds Species SN. Cyperus rotundus SN. Cynodon dactylon SN. Echinochloa crusgalli CN. purple nutsedge CN. Bermuda grass CN. barnyard grass sedge grass grass perennial perennial annual (Holm, et.al., 1977) Worlds Worst Weeds Major Weeds Species SN. Echinochloa colona SN. Eleusine indica CN. Jungle rice CN. goose grass grass grass annual annual SN. Sorghum halepense CN. Johnson grass grass perennial (Holm, et.al., 1977) Worlds Worst Weeds Major Weeds Species SN. Panicum maximum SN. Eichhornia crassipes CN. Guinea rice CN. Water hyacinth SN. Imperata cylindrica grass broadleaf CN. cogon grass annual annual grass perennial (Holm, et.al., 1977) Worlds Worst Weeds Major Weeds Species SN. Lantana camara CN. lantana broadleaf perrenial SN. Digitaria sanguinalis SN. Amaranthus spinosus CN. Large crab grass CN. Spiny amaranth grass broadleaf perrenial annual (Holm, et.al., 1977) Worlds Worst Weeds Major Weeds Species SN. Paspalum conjugatum CN. carabao grass SN. Cyperus esculentus grass CN. Yellow nutsedge perrenial SN. Rottboellia cochinchinensis sedge CN. Itcg grass perrenial grass perreneal (Holm, et.al., 1977) Economic cost of weeds Effects of Weeds on Human Affairs Losses due to weeds exceeds the losses from any other agricultural pest. Weeds = 45%; insects = 30%; disease = 20%; and others = 5% In the Philippines, losses were estimated at 11% for the dry season and 13% for the wet season in rice production. Effects of Weeds on Human Affairs Impact of weeds in the environment Effects of Weeds on Human Affairs If it weren’t for weeds, the world would have lost more topsoil than it has to date, and humankind might have suffered mass starvation by now. Why? Because the plants we call weeds do a vital job in ecosystems: they quickly establish in, protect, and restore soil that has been left exposed by natural and human-caused disturbances. Impact of weeds in the environment Effects of Weeds on Human Affairs Protect the soil from erosion Replenish organic matter, and feed and restore soil life Absorb, conserve, and recycle soluble nutrients that would otherwise leach away Absorb carbon dioxide from the atmosphere (see sidebar) Restore biodiversity Provide habitat for insects and animals Impact of weeds in the environment Effects of Weeds on Human Affairs Weeds can cause all of the following damage to the environment: compete with and take over native plants destroy native wildlife habitat and reduce natural food supplies make fires hotter and more destructive hide feral animals and make them difficult to control damage waterways and water quality. Impact of weeds in Human Health Effects of Weeds on Human Affairs Potential healtheffectsdueto productionsystem Presenceof morphological adaptations(spines, thorns) Medical valuesuchastreatmentfor allergiesanddermatitis Lossof workerproductivity  Reproduction and Establishment of Weeds GERMINATION The resumption of the active growth of the embryo in the seed or plantlets/buds in a tuber (stem) SEED GERMINATION PROCESS 1. Water imbibition 2. Enzyme activation 3. Initiation of embryo growth 4. Rupture of the seedcoat 5. Seedling emergence Weed Seed Germination Factors Influencing Germination 1. Light Photoblastism – classification of seeds based on their sensitivity for light Categories: 1.Positive photoblastism – seeds only germinate under light 2.Negative photoblastism – seeds germinate only in the dark, light inhibits germination 3.Light sensitivity – seeds germinate under light as well as in the dark  Weed Seed Germination Factors Influencing Germination 2. Temperature 3. Nitrate – stimulate germination of weed seeds, also with light 4. Gaseous Environment - Most species fail to germinate under reduced oxygen conditions (Corbineau and Côme, 1995) -Carbon dioxide levels are usually not higher than 0.5-1% (Karssen, 1980-1981). CO2 can have a beneficial effect on germination of seeds, but also a negative effect, depending on species and circumstances. 5. Moisture content - Depending on the weed species, dessication of seeds either improves germination or does not affect germination at all  Weed Seed Germination FACTORS AFFECTING ASEXUAL REPRODUCTION BY WEEDS 1. SOIL TEXTURE - lighter soils (bigger particle size) enhances better tuber/ rhizome development 2. DAYLENGTH exposure to short daylengths stimulates tuber formation - the daylength favorable to flowering favors tuber production - the daylength favorable to vegetative growth does not favor flowering 3. LIGHT INTENSITY - higher light intensity favors vegetative propagule development 4. SOIL NUTRIENT STATUS - mineral sufficiency favors asexual more than sexual reproduction-  Weed Establishment The soil is a natural “seed bank” Echinochloa crus-galli Rottboellia cochinchinensis Amaranthus spinosus Eleusine indica 42, 388 seeds 5,048 seeds 3,272 seeds 4,889 seeds  Weed Establishment Factors affecting weed establishment 1. Magnitude of weed seeds in the soil 3-3.512 M/ha - Koch, 1969 -Vega & Sierra, 1970 804 M/ha - Robinson, 1949 142.3 M/ha - Robert and Dawkins, 1967 204 M/ha Weed Establishment Factors Affecting Weed Establishment 2. Weed Germination COMMON VEGETATIVE PROPAGULES OF WEEDS TUBERS/ BULBS Cyperus rotundus, Scirpus maritimus RHIZOMES Imperata cylindrica, Paspalum distichum STOLONS (RUNNERS) Cynodon dactylon OFFSHOOTS (SUCKERS) Pistia stratiotes, Eichhornia crassipes Tubers of Cyperus rotundus Rhizomes of Suckers of Imperata cylindrica Pistia stratiotes Stolons of Cynodon dactylon  Weed Establishment Factors affecting weed establishment 3. Competition The struggle between two or more plants for the limited resources in the environment.  Weed Establishment Dormancy and Allelopathy DORMANCY The inability of a seed or a vegetative propagule to germinate even under favorable conditions Causes: PHYSICAL and/or PHYSIOLOGICAL ! In many cases viable seeds are called dormant when they are simply not germinating.  Weed Establishment Dormancy and Allelopathy BREAKING SEED DORMANCY IN THE FIELD Hard seed coats : alternate wetting and drying : microbial decomposition Immature embryo : after-ripening under natural conditions Germination inhibitors : leaching of the inhibitor to the soil Dormancy explains for the never-ending emergence of weeds in the field  Weed Establishment Mechanisms of dormancy A. Physical (structural)- impermeability to water or Categories of seed dormancy (based oxygen due to hard seed coat on the seed behavior) B. Physiological- caused by immature embryo (needs A. Innate- inherent property of mature ripening period) seed as it leaves the mother plant C. Presence of growth inhibitors in the seed coat or hull or in the embryo itself B. Induced dormancy- occurs when a non-dormant seed becomes dormant Factors affecting seed dormancy after exposure to specific A. Temperature environmental conditions B. Water C. Enforced dormancy- limitations of the habitat or environment prevent C. Oxygen germination. Removing the limitation D. Light allows germination to occur. E. Chemical inhibitors  Weed Establishment Dormancy and Allelopathy ALLELOPATHY Allelopathy refers to the beneficial or harmful effects of one plant on another plant, both crop and weed species, from the release of biochemicals, known as allelochemicals, from plant parts by leaching, root exudation, volatilization, residue decomposition, and other processes in both natural and agricultural systems. Allelochemicals are a subset of secondary metabolites not required for metabolism (growth and development) of the allelopathic organism. Allelochemicals with negative allelopathic effects are an important part of plant defense against herbivory (i.e., animals eating plants as their primary food) (Fraenkel 1959; Stamp 2003). The different release pathways and effects of allelochemicals. The allelopathy plant (left) can release allelochemicals through four pathways (black arrows): leaching by rain (P1), decomposition of plant residues (P2), exudation from roots (P3) and volatilisation (P4). The allelochemicals can affect the test plant directly (red arrows) or indirectly through their effect on soil biota (dashed red arrows). Soil biota can also affect allelochemicals, such as through conversion or degradation of allelochemicals  Weed Establishment Weed Dispersion - weeds reproduce either through seeds, or vegetative means -weeds that produce mainly through seeds, photoperiod, vegetative growth, temperature, DISPERSAL and growth regulators influenced that extent of flowering seed The movement of plants and animals from one area to another DISPERSAL UNIT A structure, together with its accessory parts, which is separated from the mother plant, and functions to perpetuate its kind Examples : seeds, vegetative propagules (tubers, rhizomes, stolons, off-shoots, leaves, etc.)  Weed Establishment Weed Dispersion AGENTS OF DISPERSAL 1. WIND - light minute seeds, flattened structure, wing-like outgrowth, feathery structure, hairy structure 2. WATER - light, buoyant seeds 3. EXPLOSIVE MECHANISMS - shattering ability 4.ANIMALS - weeds with edible and fleshy fruits, with sticky substances or with hooks 5. MAN - through clothes, shoes, cultural practices, deliberate dispersal  Weed Establishment Means of weed seed dispersal Zoochory- animals anemochory- air/wind Hydrochory- water Myrmecochory- ants  Example of seeds that have special adaptations aiding their dispersion Competition Crop-Weed Competition Weed Competition - The struggle between two or more plants for the limited resources in the environment 2 types of competition Intraspecific completion Interspecific competition - A competition that happens among plants of - A competition that happens between the same species different species Ex. Cyperus rotundus vs Cyperus rotundus Ex. Cyperus rotundus vs Portulaca oleracea  Competition Crop-Weed Competition Weeds compete for: Competition for Nutrients (1) Nutrients Fertilization favors weed growth more than crop growth (2) Water Nitrogen is the most critical nutrient for competition (3) Light Most weeds are very responsive to nitrogen application The Pistia sp. Is not responsive to N application Crop-Weed Interaction CriticalThreshold Level (CTL) - Refers to the weed density (population) beyond which significant reductions will be incurred by the crop. - refers to the presence of weeds above a certain density that will cause a significant reduction in yield. - The weed density, higher than which, significant yield losses will be incurred Crop-Weed Interaction A short CPC is more advantageous to the crop since it will only suffer the harmful effects of weed competition for a short time. When the crop has passed its CPC, then it will not be anymore be very affected by the presence of weeds, hence, weeding will not be anymore intensive. When CPC is ZERO, there is no competition, implying that there are no weeds in the field. Crop-Weed Interaction Critical period for weed control (Madrid et al, 1972) Crit. Period Days to maturity Corn 49 days 120 Mungbean 21-35 days 60-65 Soybeans 42 days 105 Upland rice (HYV) 40 days 120 Low land rice (HYV) 30-40 days 120 Crop-Weed Interaction FACTORS AFFECTING COMPETITION (the competing ability of the crops against weeds) 1. Weed Species 2. Weed Density 3. Duration of Competition 4. Seeding method 5. Crop variety and selection 6. Level of nutrition 7. Environment  Crop-Weed Interaction Factors Affecting the D egree of Yield losses due to weeds Crop Factors (competing ability) Weed Factors a. Weed density population b. Weed composition c. Competing ability Environmental/ Management Factors a. Season (wet or dry) b. Planting methods (direct seeding or transplanting) c. Water regime (rain fed, irrigated, upland, lowland) d. Land preparation e. Cropping pattern Crop-Weed Interaction Weed Population Shift (factors) 1. Weed Control Method 2. Water Management 3. Fertilizer management 4. Change in Crop or Cropping System  Integrated Weed Management Definition of terms Weed Prevention – those measures taken to prevent or forestall the introduction and spread of weeds Weed Control - is the process of decreasing weed infestation (or reducing weed population) below the critical threshold level (CTL) so that yield of crops is not affected. Weed Eradication – elimination of all plants and plant parts of a weed from an area (seeds, vegetative propagules) Weed Management - involves the utilization of methods of prevention and to keep weed population below the economic threshold level, at the same time reducing the cost and harmful effects.  Integrated Weed Management Definition The utilization of all feasible methods of prevention and control, in a harmonious combination, including the maximization of mortality factors to keep weed population below the critical threshold level, but at all time the cost and harmful effects to the environment are kept to the minimum. It is a method whereby all economically, ecologically and toxicologically justifiable methods are employed to keep the harmful organisms below the threshold level of economic damage, keeping in the foreground the conscious employment of natural limiting factors (FAO). AIM : to shift the crop-weed balance in favor of the crop  Integrated Weed Management Principles of Weed C ontrol 1. The aim of any weed control program is to reduce weed population at levels that will not be detrimental to the crop. 2. Weed control measures should be directed to organs responsible for reproduction and spread including the weed seeds in the soil. 3. Weed control measures should be started early in the season and sustained until such time when the crop can compete favorably with the weeds 4. The weed control program should ensure maximum weed mortality but at the same time with minimum cost and less harmful effects to the environment.  Integrated Weed Management METHODS AND TECHNIQUES IN WEED MANAGEMENT 1.Preventive methods or approaches that reduce production and germination of weed seeds and vegetative propagules and minimize their establishment and spread. Example: a)Use of high quality and disease and weed seed-free planting materials. b) control of weeds before they produce seeds or vegetative propagules. Weeds should be controlled before they flower or even earlier to prevent their seeds from spreading.  Integrated Weed Management METHODS AND TECHNIQUES IN WEED MANAGEMENT 2.Physical/cultural methods directly destroy weeds , and this often involve the manipulation of the environment in the field to control weeds. a)Land preparation and management of weed seed and vegetative propagules reserves/banks in the soil. Thorough land preparation is essential for providing a weed - free condition which is favorable for planting and crop growth. b)hand weeding/slashing. In this method, weeds are controlled by uprooting or with the use of various small local hand implements by slashing.  Integrated Weed Management METHODS AND TECHNIQUES IN WEED MANAGEMENT 2.Physical/cultural methods directly destroy weeds , and this often involve the manipulation of the environment in the field to control weeds. c)Hoe weeding. This method can be accomplished in less time compared with uprooting of weeds. It is suitable for many vegetable crops and is used as supplementary control to the other method. d)Inter-row cultivation. This may be done with animal or tractor-drawn implements. However, this need to be supplemented with hand weeding or hoe weeding for the control of weeds along crop rows.  Integrated Weed Management METHODS AND TECHNIQUES IN WEED MANAGEMENT 2.Physical/cultural methods directly destroy weeds , and this often involve the manipulation of the environment in the field to control weeds. e)Mulching – mulching with soil, organic materials or plastic provides considerable control of some weeds by reducing light available to the crops and serving as a barrier to weed emergence. f)Water management of Flooding. This method is effectively used in transplanted lowland rice. Many weed species will not germinate under submerge conditions.  Integrated Weed Management METHODS AND TECHNIQUES IN WEED MANAGEMENT 2.Physical/cultural methods directly destroy weeds , and this often involve the manipulation of the environment in the field to control weeds. g)Use of competitive crop varieties/cultivars. A variety adapted to the locality which is characterized by an early rapid growth provides some measure of weed control through its competitive advantage. h)Multiple cropping –This may involve spatial (intercropping) or temporal (crop rotation or sequential cropping) combinations of crops in an area in one year.  Integrated Weed Management METHODS AND TECHNIQUES IN WEED MANAGEMENT 3.Chemical control – This method involves the use of herbicides for selective control of weeds with minimum or no injury to the crop. The use of herbicides substantially reduces the labor requirement for weed control. Classification of Herbicides A. Time of Application 1.Pre-plant herbicides – herbicides applied after land preparation but before the crop is planted.  Integrated Weed Management METHODS AND TECHNIQUES IN WEED MANAGEMENT 3.Chemical control – This method involves the use of herbicides for selective control of weeds with minimum or no injury to the crop. Classification of Herbicides A. Time of Application 2.Pre-emergence herbicides – the chemical is applied after the crop is planted but before the weeds of the crop emerge. 3.Post-emergence herbicides – the herbicide is applied after the crop or the weds have emerged.  Integrated Weed Management METHODS AND TECHNIQUES IN WEED MANAGEMENT 3.Chemical control – This method involves the use of herbicides for selective control of weeds with minimum or no injury to the crop. Classification of Herbicides B. Movement of herbicides in Plants 1.Contact herbicides – herbicides whose phytotoxic effects are manifested at the sites on the plants where the spray droplets are deposited. 2.Translocated herbicides – herbicides whose phytotoxic effects are manifested at and away from the sites on the plant where the spray droplets are deposited. The herbicide is moved to other parts of the plant.  Integrated Weed Management METHODS AND TECHNIQUES IN WEED MANAGEMENT 3.Chemical control – This method involves the use of herbicides for selective control of weeds with minimum or no injury to the crop. Classification of Herbicides C. Selectivity 1. Nonselective herbicides – herbicides that kill all plants 2.Selective herbicides - herbicides that kill some plants leaving others practically unharmed.  Integrated Weed Management METHODS AND TECHNIQUES IN WEED MANAGEMENT 4.Biological control is the deliberate use of weeds natural enemies, such as insects or pathogens, to suppress the growth or reduce the population of the weed. a.Classical approach – use of host specific damaging biotic agents from the country of origin of the imported problem weed species. b.Inundative approach –this includes augmentation and bioherbicides approaches. Natural enemies already present in the area where the problem weed species occur often do not cause sufficient damage to effect adequate control of the weed because their population is low. These natural enemies maybe mass reared and then released in high numbers to control weeds. Chromolaena odorata stem gall Cecidochares connexa  damage Pareuchaetes pseudoinsulata  Lantana camara plant Mindanao, 1985 Uroplata girardi Damage by Uroplata girardi Passi, Iloilo 1989. Salvinia molesta Cyrtobagous salviniae M ethods of C ontrol (advantages and disadvantages) 1. Mechanical Method Ex. Hand weeding 2. Cultural Method Advantage - High precision and 3. Biological Method selectivity 4. Chemical Method Disadvantage - Laborious Ex. Machineries Advantage - Make job easier Disadvantage - Could kill the plant in the furrow M ethods of C ontrol 1. Mechanical Method Mulching, flooding, use of cover crops, change 2. Cultural Method in crop/ variety, population density manipulation, flaming, thorough land preparation, inter-row 3. Biological Method cultivation 4. Chemical Method Advantage - Materials are found in the farm Disadvantage - Availability, mastery, laborious M ethods of C ontrol 1. Mechanical Method 2. Cultural Method 3. Biological Method More sustainable method of control and less health 4. Chemical Method risk, however, the effect could be delayed Ex. Humans Ex. Insect Ex. Pathogen Advantage Advantage Advantage - Good influence for - pollinators - If host and weed control Disadvantage inoculum do not Disadvantage - If they carried weed match, no problem - laziness, tardiness, if not seeds it may fall off the Disadvantage managed weed could field - If host and inoculum possibly mass produce matched, it may be disseminated by wind M ethods of C ontrol Advantage 1. Mechanical Method - Biological Control Agents (BCA) are active 2. Cultural Method - Host specific - Reproduce faster than weeds 3. Biological Method Disadvantage 4. Chemical Method - Takes time, effort and money to identify a BCA - Can control only one weed species - Capable of mutation Attributes of BCA - Specific in the weeds - Able to control the weed effectively - Should be highly adapted to local conditions - Free from predators and parasites - Peak of abundance of BCA should coincide to the peak of abundance of the host M ethods of C ontrol 1. Mechanical Method 2. Cultural Method 3. Biological Method Advantage - Very effective since it is a chemical 4. Chemical Method Disadvantage - Wrong target organism - Overused could be toxic to plants Herbicide – chemicals that is used to kill weeds/ plants in general (Latin) Herba – plant; caedere – kill  THANK YOü! Department of Plant and Soil Sciences College of Agriculture and Agri-Industries Caraga State University Ampayon, Butuan City, Agusan del Norte, Ph 39