Integrated weed management importance.pptx

Integrated weed mangemeny

1. Unit: 1 Introduction to Integrated Weed Management Rationale/Relevance Weed management should aim at maximization of profit by reducing the risk of damage to crops and environment (soil and water ). A large number of herbicides have replaced or in some cases supplemented traditional practice of hand weeding towards weed control and economization of overall production cost. The chemical method though proved more promising, has led to many problems such as Weed flora shift, Insurgence of herbicide-resistant weeds, Preponderance of perennial weeds, Inhibition in growth of non-target micro-flora, and Residue problem in environment No single method could reach to the desired level of weed control efficiency in certain location or across locations mainly because of the huge diversity of weeds in crop fields .

2. Rationale/Relevance……………………. There also occurs a continuous dynamics both in population and biomass accumulation of weeds in crop-field ecosystem on temporal scale mainly due to changes brought about by man in crop cultivation/management practices. It has been observed that today's weed of minor importance assumed importance gradually and became a major weed of regional or national concern in course of time. All these have led to the evolution of integrated weed management (IWM), which means managing a population below a threshold level, which may not cause substantial economic damage to crops. IWM is a method whereby all economically and ecologically justifiable methods are employed to keep the weed below the threshold level of economic damage ( Jaya Kumar and Jagannathan , 2003). The concept is that it uses holistic approach of technologies to produce optimum crop yield at a minimum cost with due consideration of ecological and socio-economic constraints under a given eco-system.  

3. IWM Approach Integrated weed management combines rational adoption/use of direct and indirect weed control strategies to take care of weeds in totality (i.e. to match the diversity of weed species in a situation). Direct weed control strategies include Physical (manual & mechanical) Chemical mean includes effective use of herbicides It is fact that herbicide is an important component in IWM, but their doses should be restricted to low enough, which may not cause environmental degradation. Indirect control implies Cultural or agronomic practices: crop species & variety; ecological suppression of weeds by changing cropping systems or using sound crop rotation and/or better crop management techniques; water management; use of bio-agents.

4. IWM approach….. Integration of weed control methods should necessarily be based on their suitability, compatibility and feasibility under a specific crop-weed situation. Each method included has its own role to play in the overall weed management program and its impact must be analyzed in relation to yield loss and weed population growth, subsequent spread, and possible future weed shift. The methods chosen should be mutually compatible enough with each other, must support each other and match the diversity of weed species present in a crop field or a situation . They should be favourable to crop growth, but unfavorable to weeds (i.e. they must favour crop growth at the cost of weed growth) and should give effective and long-lasting/continuous control of weeds under a certain situation.

5. Usefulness/advantages IWM is a more practical approach more effective in the long run since combination of methods will take care of weeds in totality and prevents seed production and reduce the weed seed bank. It provides longer and continuous control of weeds than any individual method since it normally overcomes the existing gaps of individual method of weed control applied in isolation. It may reduce or eliminate the chance of occurrence of weed flora shift, herbicide-resistant weeds, dominance of perennial weeds etc. It is environment- or eco-friendly. It may to some extent be complementary to integrated pest management (IPM) through continuous control of weeds, which otherwise allow/cause many insect pests and diseases to harbor. It may generate higher net income/return in the long run particularly under higher cropping intensity. It is much useful under high cropping intensity. It has enough flexibility/resilience that it can incorporate innovative and practical experiences of the farmers. It is developed for a whole farm, which includes field bunds, irrigation channels, roads/paths, and other non-crop surroundings on the farm and, therefore, prevents possible dispersion of weeds from adjoining bund, roads, channels etc.

6. Limitation/disadvantages An IWM approach may not be uniformly applicable to all crops across locations. It is highly site-specific and crop- or cropping system-specific based on a host of factors comprising of soil, crops, climate and production/management practices adopted. Integrating methods of weed control mutually compatible, supportive to each other and matching the diversity of weed species is not an easy task. A model IWM designed for certain situation may not be operative constantly or repetitive over the years, in all cropping system and agro-ecology. It is more of a concept and as such not a method of weed control in true/pure sense. Its efficiency may vary based on fluctuation in the efficiency of weed control methods integrated over time and space. Integration of different methods of weed control may incur higher cost and may not evolve desired result on weed control front in the initial years and users may give up hope on IWM. An IWM approach may not be uniformly applicable to all crops across locations. It is highly site-specific and crop- or cropping system-specific based on different ecology and cultivation system. Integrating methods of weed control mutually compatible, supportive to each other and matching the diversity of weed species is not an easy task. A model IWM designed for certain situation may not be operative constantly or repetitive over the years, in all cropping system and agro-ecology. It is more of a concept and as such not a method of weed control in true/pure sense. Its efficiency may vary based on fluctuation in the efficiency of weed control methods integrated over time and space. Integration of different methods of weed control may experience higher cost under certain situation.

7. What does the IWM component contribute to : Development of weed species abundance to reduce interference with crop. Dominance of a species in the composition of existing weed flora. Substitution of a species in the composition of existing weed flora. Change in succession of species. Change in genetic structure of the targeted species. Acceptance of weed management system in relation to environment. Enhanced profitability. Improvement of overall pest management at the farm level. Social acceptance of practices those are appropriate to stake holders

8. Components of IWM  

9. Current Scenario of Weed Control In most ecosystems, herbicides have become one of the most important components in weed control. There are two reasons to explain the increased use of herbicides , the first being the widespread adoption of high-yielding varieties which created economic incentives for farmers to reduce weed infestation; and the second is the availability of cheap herbicides, indicating that the cost of weed control by herbicides in wet-seeded rice is less than one-fifth of the cost of a single hand-weeding Because of the availability of cheap herbicides, it is expected that herbicide usage will continue to increase, both in developed countries, and even in developing countries, where herbicides are currently used sparingly and farm wages are relatively low. However, this does not indicate a lack of importance for hand-weeding. Manual weeding is still the dominant weed control method in many parts of Asia, since management options for weed control are limited under diverse agro-ecological conditions (Kim, 2000).

10. Significance of IWM The growing use of herbicide needs to be checked sooner or later because of some of these serious concerns : ˃ Evolution of resistant weeds ˃ Residual effects of herbicides on following crops and soils ˃ Disappearance of some of the important weeds All these factors may well provide sufficient reason to attract public concern and anxiety regarding the negative effects of herbicides due to their excessive use. Apart from these ecological significance, some of the social significance also add up the significance of IWM in present scenario: ˃ Not every farmers are in access of specific herbicides or GMO’s to solve their weed problems . ˃ Farmers in the developing countries are still in adoption phase of herbicides. ˃ There have been the cases of adverse effect of herbicides on human health and soil. – In this regard, IWM can be one of the handy tool that can share the burden of the weed control

11. Reducing the risk of Herbicide resistance 1. Understand the biology of the weeds present. 2. Use a diversified approach toward weed management focused on preventing weed seed production and reducing the number of weed seed in the soil seedbank. 3. Plant into weed-free fields and then keep fields as weed free as possible . 4. Plant weed-free crop seed. 5. Scout fields routinely. 6. Use multiple herbicide mechanisms of action (MOAs) that are effective against the most troublesome weeds or those most prone to herbicide resistance. 7. Apply the labeled herbicide rate at recommended weed sizes. 8. Emphasize cultural practices that suppress weeds by using crop competitiveness. 9. Use mechanical and biological management practices where appropriate. 10. Prevent field-to-field and within-field movement of weed seed or vegetative propagules . 11. Prevent an influx of weeds into the field by managing field borders.

12. Strategy for preventing Herbicide resistance Strategic tillage Site-specific weed management Weed sanitation Rotation of herbicide (Site of Action) Scouting fields before and after herbicide applications Enhanced competitiveness of the crop Crop diversity

13. Unit 2: IDENTIFICATION OF VULNERABLE STAGES IN WEED LIFE CYCLE Life History of Weeds: Post-Disturbance Dominance : After severe disturbances like tillage, annuals dominate due to survival as physiologically dormant seeds. Stationary perennials also establish shortly after tillage but allocate more resources to roots, leading to lower seedling growth rates in the first year. Annual Dominance in the First Year: Annuals often predominate in the first year even if stationary perennials are abundant in the seed bank. Perennial Advantage in Later Years: Stationary perennials, with greater reserves, compete better with established perennial crops in the second season and are common in hay fields.

14. Woody Perennial Weeds: Primarily problematic in orchards and pastures. Poorly adapted to annual cropping systems due to a lack of persistent seed banks and slow growth compared to herbaceous annual crops. Environmental Conditions for Germination: Nondormant seeds may not germinate if environmental conditions are unfavorable. Seeds remain quiescent until appropriate temperatures, water, light, and other cues indicate favorable conditions. Some seeds with unfavorable conditions may enter a secondary state of innate dormancy.

15. Tillage and Weed Germination: Why tillage promotes weed seed germination? Weed Adaptation to Disturbance: Weeds are adapted to respond to soil disturbance, as small seedlings are poor competitors early in life. Germination is favored when disturbance occurs at a time when seeds are not innately dormant . Environmental Conditions in Tilled Ground: Tilled ground is warmer, experiences higher diurnal temperature fluctuations, has elevated nitrate concentration, and better aeration compared to undisturbed soil. Exposure to light during soil disturbance prompts seed germination. Nitrate as a Germination Indicator: Nitrate presence indicates enhanced mineral nutrient availability Germination of weed species, e.g., Chenopodium album and Plantago lanceolata , increases with higher nitrate concentrations.

16. Tillage and Weed Germination: Why tillage promotes weed seed germination? Gas Exchange and Oxygen Influence: Gas exchange during tillage stimulates decomposition and nitrification. Light as a Key : Light is a crucial cue promoting germination in the seed bank. Combined effects of factors like light, nitrate, and temperature fluctuations enhance germination. Cultivation Strategies: Shallow cultivation between crop rows is preferable, eliminating weeds prompted to germinate without cueing additional seeds. Deep cultivation brings up seeds that germinate due to disturbance-related cues.

17. Survival in the Soil Seed Bank: Persistence in the Seed Bank: Seeds of most annual and stationary perennial weeds persist in the seed bank for several years. Many remain viable for decades under favorable conditions. 2.Sources of Seed Mortality: Factors affecting seed mortality include: Action of seed predators such as vertebrates, invertebrates, fungi, and bacteria. Physiological aging and exhaustion of reserves through respiration. 3. Influence of Seed Predators: Predation by seed predators, including vertebrates and invertebrates, contributes to seed mortality. 4. Pre-dispersal Seed Predation: Before dispersal, natural enemies may consume a significant proportion of seeds. 5. Effect of Dormancy and Soil Surface: A. fatua loses dormancy more quickly at the soil surface. Seeds on the soil surface rapidly lose weight.

18. Species Survival in the Soil Seed Bank: Broadleaf vs. Grass Weeds: Broadleaf weeds often survive in the seed bank for several decades. Few grass species maintain substantial seed numbers beyond 5 to 10 years. Annual and Stationary Perennial vs. Wandering Perennials and Woody Weeds: Annual and stationary perennial weeds typically form persistent seed banks. Wandering perennials and woody weeds usually do not maintain persistent seed banks. Dormancy Mechanisms and Longevity: Species with well-developed dormancy mechanisms tend to have greater longevity. Weak dormancy mechanisms correlate with shorter seed bank persistence. Seed Size and Persistence: Small, round-seeded species tend to persist longer in the seed bank compared to species with large or elongate seeds.

19. Life Cycle Stages • Understanding a weeds life cycle provides the foundation of knowledge necessary to limit the impact of weeds in the agricultural area. • The life cycle of a weed refers to the general growth, flowering, seed production and eventual death of a plant.

20. Annual Weeds: Plant Growth and Reproduction • The germination and seedling stages of a weed life are often susceptible periods that can be targeted for weed control. • At this point, seedlings require adequate nutrients, water and light for survival; the weed seedlings must also compete with surrounding plants for these required resources. • Weed control through chemical or biological means can be very effective during this time when seedlings may be at risk due to limited resources available. • Once a weed reaches the seedling stage, provided adequate resource availability, vegetative growth up to flowering stage is quite rapid. Moreover, the onset of flowering may be earlier and last longer than the agricultural crop in which it is growing. • The extended period of flowering leads to high number of weeds seeds being produced and released into the environment. Prior to flowering, systemic herbicides can be used with the greatest effectiveness; however, once a weed reaches the flowering stage, it has reached its most resilient stage in life.

21. Perennial Weeds: Plant Growth and Reproduction • With improving technology into sustainable agriculture, conservation tillage has become widely practiced. • The adoption of this farming practice has required the farming community to become knowledgeable not only in annual weed life cycles but also in the life cycles of perennial weeds. • Recent research suggests a shift from annual to perennial weed dominance within conservation tillage systems, in part, due to less soil disturbance which is favorable to perennial species. • If perennials germinate from seeds, annual weed control methods may be effective for newly emerged weeds. • However, if a perennial grows from a vegetative structure, new management tactics must be employed. • Perennial weed control is most effective during active growth of the plant, except during early development or as the plant enters the flowering stage. • Repeated control tactics rather than one method, applied during these susceptible periods of perennials lifecycle can achieve control to lessen crop damage by the weed.

22. Factor affecting weed distribution in space and time

23. Weed Competition and Critical Stages of Crop Growth Competition is nothing but the struggle for existence and superiority. Competition is relationship between two or more plants in which supply of growth factors falls below their combine demand. The competition does not start as long as the growth factor is abundant in supply and does not fall below the combine demand. However it starts immediately when the growth factors falls sort in supply. Crop weed competition occurs in two broad spectrums: 1. Direct Competition: For nutrient, moisture, light and space 2. Indirect Competition: Through exudation and/or production of allelopathic chemicals.

24. Components of the overall competitive effect In an infested field, it is possible to identify different components of the overall competitive effect. Intraspecific competition between plants of the cultivated species. Interspecific competition between plants of cultivated species and weed species. Interspecific competition between the plants of different weed species. Intraspecific competition between the plants of the same weed species.

25. Competition between weeds and crops is expressed by altered growth and development of both species. Interspecific competition occurs when two or more species coexist in time and space and simultaneously demand a limited resource . Intraspecific competition occurs when two or more plants of the same species coexist in time and space and simultaneously demand a limited resource.

26. General principles of crop weed competition: Weed competition is most serous when the crop are young (e.g. seedling to tillering , branching or early flowering stage) Competition is likely greater between the plants of similar morphology and growth behavior A moderate infestation of weeds is sometimes as serious as heavy infestation Crops as well as weeds vary in their competition ability and similarly, the crops, cultivation too There is always a critical period of weed competition in crop

27. General principles of crop weed competition… 6. The probable role of a growth factor on the magnitude of weed competition in crop varies across the season and situation 7. Weed competition is always indirect in nature while allelopathy is direct in nature 8. Plant competition both under and above ground 9. Competition can be intra specific, inter specific and inter generic Crops are harmful to weeds as weeds are to crops depending to a large extent on the one that established first C 3 or C 4 physiology is less important in competition than other factor Competition during first days or weak after crop emergence is critical Crop cultivar shows great variation in competitive ability

28. 1. Competition for nutrients Plants compete mostly for nitrogen, phosphorus and potassium and many others. Weed usually absorb mineral nutrients faster than many of our crop plants and accumulate them in their tissue in relatively large amounts. Nutrient removal by weeds during the first 30 days of maize growth as 59 kg N, 10 kg P and 59 kg K per hectare,, which was 7—10 times more than the nutrient removal by the crop. – Weed possess not only a capacity for heavy nutrient absorption and accumulation but also gather tremendous quantities of dry matter.

29. In weedy field of sorghum Weeds: 46.1, 18.3 and 47.7 kg N P 2 O 5 and K 2 O ha -1 respectively Crop: 23.8, 9.4 and 46.8 kg N P 2 O 5 and K 2 O ha -1 respectively (Source: Sankaran and Mani, 1972) In rainy season weeds removes Weeds: 41.69, 10.97 and 66.77 kg N P 2 O 5 and K 2 O ha -1 respectively (Source: Pandey et al., 1981)

30. 2. Competition for soil moisture Competition for soil moisture is particularly the problems in the dry farming In a dry spell , crop plant exhibit the moisture stress symptoms much earlier in a weedy field than in weed free Weed have higher water requirement than crops Chenopodium album have consumptive use of water = 550 mm Wheat have consumptive use of water = 479 mm Weed remove moisture evenly from up to 90 cm soil depth while the major uptake of moisture by wheat was limited to the top 15 cm of soil. Source: Shahi (1978) 3. Competition for light Plant architecture especially higher, location of branches and height of maximum leaf area determine the competition of light and influence the crop yield. Competition for light may even being at the very early stages of crops if there is a shedding/smothering effects by dense and crowd growth of weeds. The competition of light is become severe, if moisture and nutrients are plentiful. Eg . Rainy maize.

31. 4. Competition for space Space refers to the composite of all resources necessary for growth and their interactions Competition for the spaces is increased when the plants starts growing above ground and underground . Grass weeds Avena fatua , Phalaris minor having profuse tillering ability and dicot weeds Chenopodium , amaranthus , trianthema have profuse branching ability poses higher above ground competition Some perennial weeds also cause the underground competition for space especially for those crop which have economic part below the soil. Eg . Groundnut.  

32. 5. Competition for oxygen occur when there is low soil air. In C 4 crops Co 2 competition does not occur. But there is co 2 competition for c 3 crops, so crop does not fix co 2 and fix o 2 so there occurs photo respiration.

33. CRITICAL PERIOD OF WEED GROWTH Critical period of weed growth can be defined as that shortest time span in the ontogeny of crop growth when weeding results in highest economic returns. Or There may be certain stages in the crop growth when weeds are more harmful to crop growth and yield The short time span in the life cycle of a crop when weed causes maximum reduction on its yield or When the weed control measure if adopted may fetch near maximal or maximum acceptable to crop yield 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 without weeds. The critical period of crop-weed competition is a dynamic concept that varies in crops, location/situation and season and year of growing due to differential growth vigor of weeds and crops Higher the altitude, greater is the crop growing duration and accordingly increases the duration /length of critical period.

34. Sharma et al., (1997) found that in direct seeded rice, the critical weed competition period occurred 10-20 days after the crop emergence. In maize, during the first 2-3 weeks of emergence, weeds often completed 15-18% of their total growth, while maize put up only 2-3% of growth. Singh et al., (1980) found that 4-16 weeks period after planting sugarcane critical for competition weeds. In potato, weeding was found most essential between 2-4 weeks after planting. Delayed weeding caused considerable shrinkage in tuber yields (Gupta et al., 1979). Rice (DSR): 15-30 DAS ( Shelke et al., 1985), 15-45 DAS ( saraawat , 1989), 0-30 DAS ( Akobundu , 1987) Rice (TPR): 0-30 DAT ( Akobundu , 1987), 30-60 DAS ( saraawat , 1989), Wheat 30-45 DAS ( Saraawat , 1985), Maize: 30-60 DAS ( Saraawat , 1985)

35. Period 1: Yield loss due to presence of weed during this period is very less but increases as the period of weedy situation increases. This period varies across season of crop grown particularly under tropical and subtropical climates. The period of onset of the critical period of weed competition is likely earlier in the wet rainy season than in the dry winter season. Period 2: is the critical period of weed competition in crops and crop must be kept weed free to avoid considerable yield losses. Period 3 : It is not critical for crop weed competition but weed presence during this season causes physical interference with harvesting of crops and build up weed seed population in soil.

36. The According to Dawson (1970) where two basic types of treatments schemes of treatments should be followed. One type of treatments the crop is kept weed free for different time after planting and then allowed to become weedy.

37. Calculation of the average yield and construction of the line graph

38. Calculation of the average yield and construction of the line graph

39. Factors affecting crop weed competition 1. Timing of weed emergence (Onset of weed) The first plant that effectively obtains water, nutrient and light from a site and becomes established at that site has distinct competitive advantages over plants that develop later . The time of weed emergence, more specifically the early onset of weed association with the crops plays a crucial role in crop weed competition. In rainy season, one or two small rain was sufficient for weed germination and emergence at that time crop that are sown after occurrence of normal rainfall have high weed infestation. Yield is generally reduces by early season weed competition as compared to later. 2. Growth form Growth habit: Extent of root development, height, leaf area and branching. Growth rate: Crop or weed whoever can develop canopy faster have relative advantage over the other. Tillering (cereal crops and grassy weeds) and branching (in broad leaves weeds and pulses) habits of both crops and weeds influence the magnitude of competition Increase tillering and more branching have higher competition for above ground space and light

40. 3. Weed Density Crop yield decreases sharply with increasing weed density and dry weight Increase in weed population diverts available resources from the crop communities. Weed density is generally higher in disturbed or agricultural soil than in undisturbed soils. In upland rice: increasing the Cyperus irria density to 400 from 40 plants per square meter increased the dry weight from o.3 to 2.34 t ha -1 and increased the yield reduction from 11 to 40% over weed free check. 4. Duration of weed growth   If weeds are allowed to grow for an extended period crop yield may be drastically reduced . Weeds that are not controlled within 2—3 weeks of emergence usually affect crop yield.

41. 5. Characteristics of Weed species Similar morphology and growth pattern or more or less the similar maturity duration (total growing duration) of certain weeds as that of crops results sever competition. E.g. Phalaris minor , Avena factua +wheat . E.g. In dry areas, weeds like Circium arvense (Canada thistle) and Convolvolus arvensis (Blind weed) have been found more competitive than the annual weed species because of their deep roots and early, heavy shoot growth . 6. Characteristics of Crop species Crops and their varieties differ in their competing ability with weeds. E.g. High tolerance of barley to competition from weed is assigned to its ability to develop more extensive roots during its initial three weeks period than the other grains.

42. Unit: 4 WEED THRESHOLD Weed threshold represent an integral component of an integrated weed management (IWM) system. A great deal of research has focused on estimating crop yield losses as a function of weed pressure, in order to identify the required level of control. Threshold Concept Threshold is defined as the point at which a stimulus(weed) is just strong enough to produce a response. For most of the cropland situation, weed density is the most easily quantified in a finite sampling area. The importance of period threshold lies in the understanding of the critical period during which remedial control action may be taken to avoid the crop loss.

43. Period threshold : It represents the times /stages in the ontogeny of a crop when weed presence causes maximum yield losses of crop. Quantity threshold: a. Damage threshold :The density/ population of weeds at which the weed competition produces negative effect or yield reduction is detected is called damage threshold. b. Economic threshold level : The economic threshold is the weed density /population at which the value of crop yield loss due to weed competition exceeds or is higher than the cost of control. The prime disadvantages in adopting ETL is the non-uniformity in the occurrence of weed species and its population, growth and virulence of infestation across location and years. ETL consider only density of weed but not impact of density of weeds towards seed production and future build up of population which cause serious problem in latter year. So, site specific digital map of weed distribution must be used.

44. Action threshold: The density/population of weeds at which some action must be undertaken to avoid crop yield loss is action threshold.

45. Methods for Calculation of Economic Threshold refer to Article

46. Unit :5 Weed shift A weed shift may be defined as ‘the change in the composition or relative frequencies of weeds in a weed population (all individuals of a single species in a defined area) or community (all plant populations in a defined area) in response to natural or human-made environmental change. Shifts in weeds are not new . Weed shifts have happened as long as humans have cultivated crops. Weed shifts occur when weed management practices do not control an entire weed community or population Eg . Similarly in maize continuous use of pre-emergence atrazine gives subsequent flushes of Commelina banghalensis , Brachiaria and Ageratum conyzoides . Under Indian conditions, Phalaris minor in wheat and invasion of grasslands and pastures and other non-cropped areas with Lantana and Parthenium are typical examples.

47. Why Do Weed Spectrums Change? Weeds are well equipped to flourish in disturbed agricultural systems. Weeds are genetically diverse and can readily take advantage of the variety of conditions created by any given crop production system. Many common weed species also have the ability to rapidly establish themselves in a field in just a couple of year’s time. This is due to weed have ability to produce viable seeds (if it is an annual) or vegetative tissues such as rhizomes (if it is a perennial) in a single growing season.

48. Weed resistance In contrast to weed shift, weed resistance is a change in the population of weeds that were previously susceptible to an herbicide, turning them into a population of the same species that is no longer controlled by that herbicide. While weed shifts occur with any agronomic practice(crop rotation, tillage, frequent harvest or use of particular herbicide), the evolution of weed resistance is only the result of continued herbicide application. Eg . In the eastern Indo-Gangetic Plains, adoption of zero tillage has resulted in an increase in population of globally-significant perennial weeds such as purple nutsedge ( Cyperus rotundus L.) and Bermuda grass { Cynodon dactylon (L.) Pers.} [Malik and Kumar 2014] The use of a single class herbicide application continuously over time creates selection pressure so that resistant individuals of a species survive and reproduce, while susceptible ones are killed.

49. WEED MANAGEMENT PRINCIPLES TO REDUCE WEED SHIFTS AND RESISTANCE WEED IDENTIFICATION FREQUENT MONITORING HERBICIDE RATE AND TIMING CROP ROTATION AGRONOMIC PRACTICES –seeding date, irrigation, harvest management ROTATION OF HERBICIDES

50. Unit: 6 What is the weed seed bank? The weed seed bank is the reserve of viable weed seeds present on the soil surface and scattered in the soil profile. It consist of both new weed seeds recently shed and older seeds that have persisted in the soil for several years. Agricultural soils can contain thousands of weed seeds per area and understanding the factors impacting the dynamics of weed seedbanks can help in the development of IWM. Eg . Without competition from other plants, a single common lambsquarter ( Chenopodium album ) plant can produce more than 70,000 seeds and they are released into the soil thus causing the SEED RAIN . All these seed do not germinate the next year but their fate is governed by several factors; some germinate, some get dormant, some get decomposed and some get predated. It is estimated that out of the total seed produced only 35-40% of the seed germinate next year whereas the remaining make up the SOIL WEED SEED BANK. Thus the Seed Bank is the store of seeds buried in the soil; composed of seed produced on site and seed moved into the area.

51. A model of the dynamic of seed pool /bank in soil   The seed bank cycle(input to the seed bank are shown with black arrow and losses with white arrow.

52. Huge gap between weed seed production potential and seedling emerging exist.

53. Weed Seed Predation Insects and other organisms consume weed seeds while they are still on the parent plant and after they have been shed. Post dispersal weed seed predation has a more widespread impact on weed seed banks. Ground beetles (carabids) are among the most widely-documented and consistent weed seed consumers in agro ecosysems , but field crickets, ants, earthworms, slugs, field mice, and other small rodents also contribute significantly to weed seed predation. Microorganisms comprise another set of potential allies against the weed seed bank. Many newly-shed weed seeds are highly resistant to invasion by bacteria or fungi; however, as these seeds age and weather in the soil, their seed coats eventually become more porous, leaving the seeds more vulnerable to microbial attack.

54. Fate of Weed Seed in the Soil After a seed is shed from the parent plant, it can remain dormant or germinate. Seed with hard seed coat possess ‘innate’ dormancy and require mechanical or chemical injury and high temperature drying to break dormancy OR may require an after ripening period. ‘Induced’ dormancy results when the seed are exposed to unfavorable conditions such as high temperatures after being shed from the parent plant. ‘Enforced’ dormancy occurs when conditions favorable to weed germination are absent. Altogether, multiple types of dormancy ensure that some weed seeds will germinate and some will remain dormant for later seasons

55. Unit :7 Weed and the soil environment Sessile Nature: cannot move beyond their growth limits Immobile plants enable weed suppression through soil manipulation, as both weeds and crops compete for essential resources like sunlight, water, and nutrients. Crop-Weed Interactions: Reciprocal influences between crop plants and weeds shape competitive outcomes, with environmental conditions, especially soil factors like nutrients, pH, and water levels, playing a crucial role. Soil Conditions and Plant Abundance: Ecological studies reveal that plant abundance is influenced by soil conditions, impacting suitable germination sites. Soil manipulations can alter species densities before competitive interactions occur. Limited Focus on Soil Manipulation: Ecological Weed Management Goals: The aim is to identify soil strategies that reduce weed growth while enhancing crop productivity. This involves manipulating nutrients, pH, water levels, and other factors within the soil environment.

56. Temperature Management for Weed Control:   Crop residue retention on soil surface practical for reducing soil temperature. Elevating Soil Temperature : Effective for killing weeds, particularly seeds and resistant structures. Post-harvest burning, common in temperate regions. In tropical slash-and-burn systems, burning vegetation influences seed density. 3. Solarization Technique : Suited for hot regions, solarization involves covering soil with polyethylene sheets for weeks to trap solar energy, raising soil temperature and preventing heat stress on crops, applied before crop sowing. Irrigation before laying polyethylene tarps is crucial because it improves heat conduction and promote biological activity. The combination of solarization and irrigation creates conditions conducive to suppressing weed growth through both physical and biological mechanisms. Field experiments globally show solarization reduces viable seed densities and weed emergence in subsequent crops. Solarization effects on germinable seeds concentrated in upper soil layers.

57. Emergence of annual grass and other species significantly reduced with increased solarization duration. Perennial sedge ( Cyperus rotundus ) showed resistance to solarization . Disadvantages: It include reliance on expensive polyethylene mulch, incomplete control of certain weeds, plastic disposal challenges, and temporary field removal. High cost makes it suitable for high-value crops with significant weed control expenses. Research needed for cost reduction through photodegradable or biodegradable mulch materials.

58. Water Management for weed control Drainage and irrigation are widely used to improve soil moisture conditions for crop production. Conversely, water can be added or withheld to prevent weed germination, or to stress or kill weeds. Weed suppression through moisture management can be achieved through non-selective methods, used when crops are absent, and selective methods, used when weeds are growing in mixture with crops. The reactions of individual weed species and weed communities to moisture manipulations are determined by the timing, location, and magnitude of alterations of soil moisture conditions.

59. Flooding Impact on Weed Germination, Growth, and Survival : Flooding severely reduces these aspects for weed species unadapted to anaerobic conditions. It is used in certain agroecosystems to suppress perennial weeds before or after crop production. Case Study : Sorghum halapense control through flooding: McWhorter (1972) observed that flooding soil for 14 days at a water temperature of 20° C prevented the establishment of the perennial grass Sorghum halapense from rhizomes. Practical application on thousands of hectares in the lower Mississippi River valley, infested with S. halapense . Suggested effective control by flooding for two weeks in high-temperature summer months or four weeks in March/April, allowing subsequent summer crop production. Practical Considerations: Flooding duration and timing crucial for effective weed control.

60. Fertility Management for weed control At least 14 mineral elements are essential for the growth and development of higher plants. Applications of mineral elements to soil, especially nitrogen (N), phosphorus (P), potassium (K), and sulfur (S), often improve crop yield. Fertilization consequently plays a key role in crop production. Nitrogen is the nutrient whose supply most often limits the growth and yield of agricultural plants, and it is applied in the greatest quantities as synthetic fertilizer

61. Spatial variation in nutrient availability: Placement of fertilizer in bands close to crop rows is a method of concentrating nutrients for use by crops; It may also reduce nutrient availability to weeds not growing near the bands. Banding fertilizers within the row of such crops as bean, soybean, peanut, wheat, alfalfa, and rice has been shown not only to increase crop yield compared to broadcast applications, but also to reduce weed density and biomass ( DiTomaso , 1995). Advantages of fertilizer banding are generally more pronounced for nutrients applied in a deep band (e.g., 5–7 cm below seed level) than for nutrients applied in a band on the soil surface ( DiTomaso , 1995), perhaps because crop seedlings tend to emerge from deeper in the soil profile than do weed seedlings.

62. Temporal Variation in nutrient availability: Weed and crop species have different abilities to absorb nutrients at different growth stages, so the timing of fertilizer application can have strong effects on weed and crop performance. Delayed fertilizer application increased crop biomass as much as 70% and reduced weed biomass as much as 50%, compared with early application of the same total quantity of fertilizer. In cases where the peak period of nutrient absorption by a crop occurs after the period of maximum nutrient absorption by an associated weed Delayed application of fertilizer may starve the weed of nutrients during critical initial growth stages of weeds and better match the timing of crop nutrient demand.

63. Crop Residue management: Crop residue management are important factors affecting soil chemical, physical, and biological characteristics. Detrimental effects of crop residue are greater for small-seeded species than larger-seeded species. Residue management offers important opportunities for weed suppression. In order to generate enough residue to inhibit the weed growth, supplemental crops need to be grown in the cropping system. E.g. Green manuring crops, Cover crops. The most important application of allelopathy involves the use of crop residue to suppress weed germination, establishment, and growth. Eg . Wheat straw residue helps to manage weed.

64. Integration of soil and weed management Soil Amendment systems Organic matter amendments have been shown to render crops less attractive to insect pests and reduce crop disease problems by promoting better soil structure, more vigorous root systems Soil solarization , flooding, banded nutrient applications, cover cropping with allelopathic species, and other practices clearly can play desirable roles in regulating weed populations, but the soil is more than just a medium in which to suppress and kill weeds — it is a resource that must be enhanced and protected for long-term crop production.