- High fertility conditions coupled with slow growth rate of high yielding dwarf varieties are conducive for rapid growth and proliferation of weeds.
- Weeds also flourish in aquatic systems and non-cropped areas like industrial sites, road sides, railway lines, air fields, water tanks and waterways, etc. Thus all plants may become weeds in particular situations, when we do not want them there.
Why weed problem is not considered alarming?In different systems of rice culture, often the yield losses due to weeds exceed those of the diseases and insect pests. However, as damage to the rice crop due to weed competition is not directly visible, the weed control is often ignored in modern rice production technology.
Factors Influencing Weed Competition
- The competitive ability of a weed may be viewed as the overall integration of root and shoot growth or surface area, the metabolic activity, and the distribution in time (when the weed is growing in relation to the rice plant) and space (location of roots and foliage in relation to the rice plant) of the organs that acquire the resources.
- The competition between crops and weeds is mainly through the capture and utilization of resources and depends on time of germination, rate of growth of the plants and the spatial arrangement of their foliage and roots.
- onset of competition is determined by the time when a resource becomes limiting to either the weed or rice plant.
- This forms the basis for type of weed control method to be adopted under field conditions
Soil factorsMany soil factors modify weed competition, while soil nutrient status, influences the nature and duration of competition in dry seeded rice. Usually, weeds grow better under adequate levels of nutrients, thus making them more competitive, indicating that weed control becomes more important with increase in fertilizer application.
Environmental factorsDepending on the rice variety used, competition for light appears to intensify as the weeds grow taller than the rice crop. With decreased light transmission ratio in dry seeded rice. grassy weeds and sedges become more competitive for solar energy than broad leaved weeds, while in wet-seeded rice, the competitive effect of Echinochloa on tillering of rice is the main factor in reducing the yield