UNIT 6. THE CONTROL OF WEEDS AND PLANT DISEASES
Weed definition
A plant is often termed a "weed" when it has one or more of the following characteristics:
- Little or no recognized value (as in medicinal, material, nutritional or energy)
- Rapid growth and/or ease of germination
- Competitive with crops for space, light, water and nutrients
Weed control is important in agriculture. Many strategies have been developed in order to contain these plants. Methods include hand cultivation with hoes (azada), powered cultivation with cultivators, smothering with mulch (abono, mantillo), lethal wilting with high heat, burning, and chemical attack with herbicides (weed killers).
Herbicides
Plant diseases
All species of plants, wild and cultivated alike, are subject to disease. Although each species is susceptible to characteristic diseases, these are, in each case, relatively few in number. The occurrence and prevalence of plant diseases vary from season to season, depending on the presence of the pathogen, environmental conditions, and the crops and varieties grown. Some plant varieties are particularly subject to outbreaks of diseases; others are more resistant to them.
Plant diseases are a normal part of nature and one of many ecological factors that help keep the hundreds of thousands of living plants and animals in balance with one another.
In general, a plant becomes diseased when it is continuously disturbed by some causal agent that disrupts the plant’s normal structure, growth, function, or other activities.
Plant diseases can be broadly classified according to the nature of their primary causal agent, either infectious or noninfectious. Infectious plant diseases are caused by a pathogenic organism such as a fungus, bacterium, virus or parasite. An infectious agent is capable of reproducing within or on its host and spreading from one susceptible host to another. Noninfectious plant diseases are caused by unfavourable growing conditions, including extremes of temperature, disadvantageous relationships between moisture and oxygen, toxic substances in the soil or atmosphere, and an excess or deficiency of an essential mineral.
A herbicide
is a chemical substance used to control or manipulate undesirable
vegetation, especially weeds. Herbicides are extensively used in
gardening, farming, and landscape turf management.
Herbicides are classified into two categories: selective and non-selective. Selective herbicides kill specific unwanted plants while leaving desirable vegetation relatively unharmed. Non-selective herbicides (total weed killers) kill all or most plant species.
A herbicide can be applied directly to the plant, applied to the soil, or sprayed onto the foliage. Herbicides are applied before, during, or after crop planting in row-crop farming to maximize crop production by diminishing the development of unwanted plants. Herbicides are also applied in ponds and lakes to control aquatic plants, in forests to prepare logged areas for replanting, and to golf courses, lawns, parks, and other areas to clear out unwanted vegetation.
Herbicides are classified into two categories: selective and non-selective. Selective herbicides kill specific unwanted plants while leaving desirable vegetation relatively unharmed. Non-selective herbicides (total weed killers) kill all or most plant species.
A herbicide can be applied directly to the plant, applied to the soil, or sprayed onto the foliage. Herbicides are applied before, during, or after crop planting in row-crop farming to maximize crop production by diminishing the development of unwanted plants. Herbicides are also applied in ponds and lakes to control aquatic plants, in forests to prepare logged areas for replanting, and to golf courses, lawns, parks, and other areas to clear out unwanted vegetation.
All species of plants, wild and cultivated alike, are subject to disease. Although each species is susceptible to characteristic diseases, these are, in each case, relatively few in number. The occurrence and prevalence of plant diseases vary from season to season, depending on the presence of the pathogen, environmental conditions, and the crops and varieties grown. Some plant varieties are particularly subject to outbreaks of diseases; others are more resistant to them.
Plant diseases are a normal part of nature and one of many ecological factors that help keep the hundreds of thousands of living plants and animals in balance with one another.
In general, a plant becomes diseased when it is continuously disturbed by some causal agent that disrupts the plant’s normal structure, growth, function, or other activities.
Plant diseases can be broadly classified according to the nature of their primary causal agent, either infectious or noninfectious. Infectious plant diseases are caused by a pathogenic organism such as a fungus, bacterium, virus or parasite. An infectious agent is capable of reproducing within or on its host and spreading from one susceptible host to another. Noninfectious plant diseases are caused by unfavourable growing conditions, including extremes of temperature, disadvantageous relationships between moisture and oxygen, toxic substances in the soil or atmosphere, and an excess or deficiency of an essential mineral.
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