Persistence of Weeds
It is the measure of the adaptive potential of a weed that enable it to grow in any environment. Weeds are both hardy and persistent. Therefore, they are difficult to control.
Weeds are the best examples of successful struggle for existence on earth advocated by Charles Darwin in the year 1859.
The persistence of weeds or weed adaptability is largely influenced by edaphic ( Soil), climatic and biotic factors which affect its occurrence, abundance , range and distribution.
1) Soil Factors of Persistence of Weeds:
The soil factors which influence persistence of weeds are soil, moisture, aeration , temperature , PH fertility level and also a cropping system.
Many weeds have adaptability to a wide range of soil environment. Many weeds can adopt and grow in soils of low fertility , very high PH ( alkali soils) or low PH ( acidic soils) waterlogged soils etc. however, crops can’t tolerate such abnormal conditions of soil. The distribution of weed species depends upon conditions of the soil as below:
E . g 1. Moist Soil Condition: Kena ( commelina spp), Maka etc.
2. Water Logged Soils: Typha, Cyperus
3. Light Soils: Cock’s comb, Piwala dhotra, Euphobia hirta ( dudhi) , Aghada etc.
4. Heavy soils: Hariali, kunda.
5. Basophiles: Weeds growing on alkali soils ( PH 7.4 to 8.5 ) E.g Alkali grass, Quackgrass.
6. Acedophiles: Weeds growing on acidic soils ( PH 4.5 to 6.5 ) E.g Hariali, Digitaria spp.
7. Neutrophiles : Weeds growing on neutral soils ( 6.5 to 7.4 ) several weed species grow on neutral soils.
2) Climatic Factors of Persistence of Weeds:
The important climatic factors that effect persistence of weeds are sunlight, temperature, rainfall, wind, etc.
Light intensity and duration are important in influencing growth, reproduction and distribution of weeds. The photoperiod governs affects flowering and time of seed setting and maturation.
It has also important bearing on evaluation of different ecotypes within weed species. Tolerance to shading is major adoption that enables weeds to persist.
Temperature of atmosphere and soil affects seed germination and dormancy which is major survival mechanism of weeds. Many weeds are hardy and tolerate extreme condition of temperature.
It has significant effect on distribution and persistence of weeds. The weed species found in desert and low rainfall areas. E. g Acacia spp. Zizyphus spp, cactus, cock’s comb, piwala dhotra etc. are different from those of aquatic environment or high rainfall area ( E. g Water hyacinth, hydrilla, cyperus iria, maka etc.)
It is the major factor in dissemination of weeds. It modifies the transpiration and evaporation losses and balance of oxygen and carbon dioxide in the atmosphere. Wind can limit or restrict the occurrence and persistence of weeds.
Climate has profound effect on persistence of weeds which can adopt to wide variety of climates. Many weeds are hardy and can tolerate adverse climatic conditions. Many of the weed are C4 plants e.g Nustedge, Hariali, Vasatvel, Portulaca spp. Amaranthus spp, wild oats, wild rice, chandvel etc. The C4 weeds can withstand low or high CO2 levels, high intensity and high temperatures.
3) Biotic Factors of Persistence of Weeds:
Plants, animals, birds, insect and disease causing organisms are the biotic factors that modify the growth of weeds and seed production in variety of way that affects weed persistence directly and indirectly. Weeds produce large number of seeds has dormancy and viability for longer period and also have dis-agreable taste and odour. All these characteristics of weeds enable them to survive even under the various effects of biotic factors.