crop weed competition - by Anjali (IGKV RAIPUR, C.G)

crop weed competition - by Anjali (IGKV RAIPUR, C.G)

1. CROP WEED COMPETITION in different cropping system, CHANGE IN WEED FLORA, VARIOUS CAUSES AND AFFECTS COLLEGE OF AGRICULTURE INDIRA GANDHI KRISHI VISHWAVIDYALAYA, RAIPUR SUBMITTED TO: Dr. M.C. BHAMBRI Chief Agronomist COA, Raipur PRESENTED BY: ANJALI PATEL PhD (Previous year) Deptt . Of Agronomy

2. CONTENT Weed Interference Competition Critical period of weed competition Competition in different cropping situation Weed Shift Weed Management In Direct Seeded Rice ( Oryza sativa L.)

3. weed Weeds are the plants, which grow where they are not wanted ( Jethro Tull , 1931 ). Weeds can be referred to as plants out of place. In the world there are 30,000 weeds species, out of these 18,000 sp. cause damage to the crops. Jethro Tull first coined the term weed in 1931 in the book “Horse Hoeing Husbandry”.

4. interference The total/whole detrimental effect of weeds on crop plants resulting from interaction with each other is termed “ interference ”. Harper (1960)

5. Different components/causes of interference are Allelospoly /competition: It involves the depletion of one or more growth resources between species growing in association in the same habitat. Allelopathy : Release of chemicals by one or more species in the association. Autotoxicity : toxicitiy within same species. Also called autoallelopathy or autoinhinition . Soil sickness : quality and yield of a crop when grown on the same land for many years together reduce . Allomediation : it involves selective herbouring of a herbivore that might selectively feed on one species and thus lending advantage to another.

6. competition Competition means that one plant utilizes the necessary environmental growth resources (water, nutrients, light and space) resulting in a shortage, which is harmful to another plant sharing the same habitat. It always implies resource limitation, a specific mechanism of interference. Muller (1971) Competition is relationship between two or more plants in which supply of growth factor falls below their combined demand. The competition is does not start as long as the growth factor is abundant in supply and does not fall below their combined demand. However, it starts immediately when the growth factor fall short in supply . Aldrich (1984)

7. concept Competition is nothing but the struggle for existence and superiority. Competition exerts a powerful force in the community, irrespective of the mechanism, tending towards limitation of the weaker competitors. Competition is a negative interaction where individuals make simulta - neous demands that exceed limited resources and, while both suffer, one individual suffers less.

8. Nature of crop-weed competition Competition for nutrients Weeds usually absorb mineral nutrients faster and in larger amount than crop plants. Competition for moisture Competition becomes critical with increasing soil moisture stress. For equal amount of dry matter weeds transpire more water than crops. Competition for light Dense weed growth smothers the crop seedlings. Crop plants suffer badly due to shading effect of weeds. Competition for space/CO 2 A more efficient utilization of CO 2 by C 4 type weeds may contribute to their rapid growth over C 3 type of crops.

9. Effect of competition duration The question of duration of competition has been addressed in two ways. The first kind of study asks, what is the effect when weeds emerge with the crop and are allowed to grow for defined periods of time? After each of these times, the crop is then kept weed free for the rest of the growing season. The second, frequently complementary, study asks, what is the effect when the crop is kept weed free after crop emergence for certain periods of time and then weeds are allowed to grow for the rest of the growing season? These studies, when combined, can be used to define what is usually called the critical weed-free period.

10. Critical period of weed competition The period at which maximum crop weed competition occurs is called critical period. It is the shortest time span in the ontogeny of crop when weeding results in highest economic returns. The time that the crop needs to be weed-free to show no detrimental effect on yield (immediately after emergence).

11. Critical period of crop-weed competition and losses in yield

12. Cont…

13. Cont…

14. Cont…

15. Cont…

16. The nature of competition intra-specific and inter-specific competition intra-specific competition between plants of the cultivated species; inter-specific competition between plants of the cultivated species and weed species; inter-specific competition between plants of the different weed species; intra-specific competition between plants of the same weed species.

17. Crop weed competition is due to Morphological similarities Seed shedding behavior Congenial environment Germination in flushes Continuous use of one group of herbicides

18. General principles in crop-weed competition Weed competition is most serious when the crop plants are young. Competition is likely greater between plants of similar morphology and growth behavior. A moderate infestation of weed in sometime as serious as a heavy infestation. Crops as well as weeds vary their competitive ability and similarly, the crops, cultivars too. There is always a critical period of weed competition in crop.

19. Cont… The probable role of a growth factor on the magnitude of weed competition in crops varies across season and situation based on the availability of resources. Weed competition is always indirect in nature, but allelopathy direct in natures. Plant competition is both under and above the ground. Competition can be intra-specific, inter-specific, intra-generic and inter-generic.

20. Factors affecting Crop-weed competition A. Weed Factors Weed species Weed density and dryweight The onset and duration of weed association with a crop B. Crop factors Crop species and crop variety Crop density Plant height and growth habit Nature and orientation of leaf Tillering / branching Root system Total growing duration

21. cont… C. Environmental Factors rainfall Temperature Light Relative humidity Cloudiness D. Soil factor Fertility pH Moisture Texture Structure Topography

22. cont… E. Biotic stress Insect pest Disease Nematode F. Crop management factor Tillage and interculture Time, method, depth of planting and row spacing Cropping pattern Fertilzation Irrigation

23. Thresholds of competition The limit above which losses will be occurs is known as threshold of competition.

24. The economic Thresholds Uygur & Mennan : Y= Where, Y is percent yield losses at a different weed density; He, herbicide efficiency; Hc , herbicide cost; Ac, application cost of herbicide; Gp , grain price and Yg , yield of weed free.

25. Cont… Stone and Pedigo : Economic threshold = Gain threshold/Regression coefficient Where, gain threshold = Cost of weed control ( Hc+Ac )/Price of produce ( Gp ), and regression coefficient (b) is the outcome of simple linear relationship between yield (Y) and weed density/biomass (x), Y = a + bx.

26. Competition in different cropping situation Rain fed cropping Irrigated cropping Sole cropping Inter cropping Low land and Up land condition Wet and dry soil Acidic and alkali soil Drought, flood and Extreme temperature Mono cropping and Intercropping Agro- foresty

27. Rain fed cropping situation:- Mostly for water Light, nutrient is not a limiting factor Irrigated cropping situation Mostly for light and nutrient Water is not a limiting factor

28. Sole and intercropping In case of intercropping competition is less for growth factor as compare to sole cropping. Individual and total weed density was reducing significantly due to intercropping systems ( pearlmillet + clusterbean and pearlmillet + mothbean ) at 25 DAS and physiological maturity as compared with sole pearlmillet . ( Ashish Kiroriwal and R.S. Yadav , 2013)

29. Low land (wet) and Up land (dry) condition More competition for light and nutrient whereas less for water in case of low land condition and vice versa in respect to up land situation & When fields are irrigated immediately after planting then weeds attain more competitive advantage over crops. Cont………

30. In water logged soils weeds are more competitive than crop plants. In submerged conditions in rice, weeds are put to disadvantage to start with. But if there is a break in submergence, the weeds may germinate and grow more vigorously than the crop, even if fields were submerged later.

31. Acidic and alkali soil In acid soils Rumex acetosella and Pteridium spp , and in saline alkaline soils Taraxacum stricta , Agropyron repens are the dominant weeds. Drought, flood and Extreme temperature Adverse weather conditions such as drought, floods and extreme of temperature intensify weed crop interference since most of our crop varieties are highly susceptible to such climatic influences where as the weeds are tolerant to their stresses.

32. Agro- foresty Weeds are unable to compete

33. Weed Shift “The change in the composition or relative frequencies of weeds in a weed population (all individuals of a single species in a defined area) or community (all plant populations in a defined area) in response to natural or human-made environmental changes in an agricultural system” Weed shifts occur when weed management practices do not control an entire weed community or population. Susceptible weeds are largely eliminated over time with continued use of the same cultural practice or herbicide. This allows inherently tolerant weed species to remain, which often thrive and proliferate with the reduced competition.

34. Why weed shift? Some species or biotypes are killed by (or susceptible to) the weed management practice, others are not affected by the management practice (tolerant or resistant), and still others do not encounter the management practice (dormant at application). Those species that are not controlled can grow, reproduce, and increase in the community; resulting in a weed shift. Any cultural, physiological, biological, or chemical practice that modifies the growing environment without controlling all species equally can result in a weed shift.

35. 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.

36. Examples of weed shifts Community shift in response to herbicide use : With the use of clodinafop in wheat weed flora was mainly composed of poa annua . Similarly in maize continuous use of pre emergence atrazine give subsequent flushes of Commelina banghalensis , Bracharia ramosa . Community shift in response to tillage change : Change from conventional to reduced tillage system often cause weed community that include increase in summer annual grasses and small- seeded summer annual broadleaves, winter annual, biennial and perennial species and decrease in large- seeded summer annual species.

37. Cont…. Population biotype shifts in response to herbicide use (herbicide-resistant populations) : in the mid- west, in many population of common waterhemp (pigweed species), biotype differed susceptibility to ALS – inhibiting herbicides. With recurrent spraying of ALS- inhibiting herbicides, population shifted from susceptibility to highly resistance biotype . With a foliar herbicide without residual activity like glyphosate , there could also be a shift within a weed species to a late emerging biotype that emerges after application. 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 ) and Bermuda grass ( Cynodon dactylon ).

38. WEED MANAGEMENT PRINCIPLES TO REDUCE WEED SHIFTS AND RESISTANCE WEED IDENTIFICATION: A weed management strategy to prevent weed shifts and weed resistance requires knowledge of the composition of weeds present. Identification of young seedlings is particularly important because seedling weeds are easier to control. FREQUENT MONITORING FOR ESCAPES: Identification and frequent monitoring can detect problem weeds early and guide management practices, including herbicide selection, rate and timing.

39. Cont… HERBICIDE RATE AND TIMING : In weed management programme the grower must be sure to use the proper herbicide rate for the particular weeds species as they may sometimes tolerant to lower doses. And also the time of application of the herbicide dose is important. CROP ROTATION : Crops differ in their ability to compete with weeds; some weeds are a problem in some crops, while they are less problematic in others. Rotation therefore would not favor any particular weed spectrum.

40. Cont…. AGRONOMIC PRACTICES : If problem weeds germinate at a specific time of year, crop seeding date can be shifted to avoid these weed populations. Delaying irrigation after can reduce germination of certain summer annual weeds. Harvest must occur before weed seed production to prevent weed proliferation. ROTATION OF HERBICIDES : Rotation of herbicides reduces weed shifts, provided the rotational herbicide is highly effective against the weed species that is not controlled with the primary herbicide.

41. Cont… Frequency of Rotation depends on weed species and escapes. There is no definitive rule on how often herbicides should be rotated. It is better to rotate at least once on the middle years or more often for perrenial crop. It can also be modified depending upon actual observations of evolving weed problems.