Weed control and management

<div class="MsoNormal" style="margin-left: .5in;"> <b><u><span style="font-size: 28.0pt; line-height: 115%;">Weed control and management<o:p></o:p></span></u></b></div> <div class="separator" style="clear: both; text-align: center;"> <a href="https://1.bp.blogspot.com/-qrzENCZbS9s/WEOw5UydwvI/AAAAAAAAANM/Hd0FSxKETjQSKYjGFQvJTpeAl1GlCg1EQCLcB/s1600/A%2B429.JPG" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="300" src="https://1.bp.blogspot.com/-qrzENCZbS9s/WEOw5UydwvI/AAAAAAAAANM/Hd0FSxKETjQSKYjGFQvJTpeAl1GlCg1EQCLcB/s400/A%2B429.JPG" width="400" /></a></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">               Weed is defined as a plant that is undesirable, unattractive or troublesome especially one that grows where it is not wanted and often grows or spreads fast or take the place of desired plants.<o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">                  The classification of weeds is important for applying weed management for a particular group of weed instead of individual weed species. Weeds are classified according to their life cycle, morphology, structure and form. According to the life cycle, weeds are classified into three groups. <b>Annua</b>l weed take one year or one season to complete their life cycle. <b>Biennial</b> weed take two years or season to complete their life cycle. <b>Perennial</b> weed take more than two years or several years to complete their life cycle.<o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">                  According to the habitat weeds are classified into two groups such as terrestrial and aquatic. According to the morphology, weeds are classified into two groups such as narrow leaved weeds and broad leaved weeds. Grasses (family Poaceae) and sedge (family cyperaceae) are the examples for narrow leaved weeds. Grasses have hollow stem and lignite alternative or opposite leaves with leaf sheath. Sedges are angular and have solid stem. Broad leaved weeds are dicot plants. The difference between broad leaved weeds and narrow leaved weed helps to use of selective control methods without injuring broad lead weeds. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">                  Correct identification, impacts and life cycle of weed are useful to idenify proper weed management. Several methods are available to control weeds. Preventive methods are used to stop the spread of weeds. Preventing the introduction of weeds and spreading is usually easier than controlling them after establishment. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">              Cultural weed control methods make the crop to be the best completer with the weeds. Planting the best crop varieties and dense crop populations and applying lime and fertilizers help to achieve the aim of the cultural weed control. It is more practicable and efficient method for controlling weeds where other methods are impossible such as within rows of rice fields. But it is difficult to distinguish weed seedlings and rice seedlings at early stages so uprooting of rice seedlings cannot be avoided. It is not practical to apply for large scale rice fields. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">                        Biological control involves the use of natural enemies to reduce the reproductive potential of weeds.  They can be weed feeders like insect feeders or disease cause organisms like fungi, bacteria and viruses to kill the invasive plants. It is environmentally friendly methods. It has ability to self-propagative so there is no need of again and again introducing them for field. Weeds are unable to develop resistance against biological methods. The damage to the untargeted pant species is minimized due to its selectivity.  As biological control agents are also dependent on the environmental conditions, it causes fluctuations on the weed populations.<o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">                        Chemical control involves the use of herbicides to kill a particular group of weed. It is an efficient method for both small scale and large scale. It supports to kill the deep rooted, vegetative propagative plants. After application, it is not allowed weed to regenerate for a considerable time period. Unlike other methods, herbicides are able to reach all places and kill the weeds.  But excess use of herbicides makes the weed to develop resistance against them. The people who apply the herbicide must have proper technical knowledge in order to apply the appropriate dose with correct dilution.  In addition to suppression of growth weed, it treats to the growth of crop plants as well as animal species. Excess use of herbicide pollutes the soil, water and the atmosphere.<o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">                        Mechanical or physical methods destroy or make the environment less favorable for seed germination and survival.  Mechanical methods are tillage, uprooting, slashing, moving, ring banking and dark stripping. It requires less time than the manual control. It is only suitable for small scale weed management. It cannot be used to control weeds growing much closer to the crop plants.  Improper tillage can damage the crop plants too. It cannot be used for soil with too dry or too wet conditions. It causes serve disturbance to the soil which leads to soil erosion. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">               Integrated weed management (IWM) involves employment of different methods of weed prevention and control. IWM is a combination of physical control, chemical control, biological control and cultural control method. It reduces the chance to the plants to adapt to the control techniques. It reduces the weed stock and extent in the soil. It is the most sustainable method of weed control and management.  But it takes relatively more tim</span><span style="font-size: 16.0pt; line-height: 115%;">e </span><span style="font-size: 14.0pt; line-height: 115%;">for the longer process. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">                        Risk of plant to be invasive is assessed by using a protocol including 32 questions.  At least 28 answers for flora are essential to evaluate the potential of risk. Each question must be marked with either yes or no. Using final percentages value for answers with yes, the plant is placed in one of following categories. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">                        >80%- very high risk<o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">                        60-80%-high risk<o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">                        40-60%- moderate risk<o:p></o:p></span></div> <div class="MsoNormal" style="margin-left: .5in;"> </div> <div class="MsoNormal"> <span style="font-size: 14.0pt; line-height: 115%;">                        <40%- low risk<o:p></o:p></span></div>

Weed control and management

Weed control and management                Weed is defined as a plant that is undesirable, unattractive or troublesome especially one t...

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Seedless non vascular plants (Phylum Pterophyta)

<div class="MsoNormal" style="margin-left: .5in;"> <b><u><span style="font-size: 26.0pt; line-height: 115%;"> Seedless non vascular plants<o:p></o:p></span></u></b></div> <br /> <div class="MsoNormal" style="margin-left: .5in;"> <b><span style="font-size: 26.0pt; line-height: 115%;">            </span></b><b><span style="font-size: 22.0pt; line-height: 115%;">(Phylum Pterophyta)<o:p></o:p></span></b></div> <div class="separator" style="clear: both; text-align: center;"> <a href="https://2.bp.blogspot.com/-zwauMEbKjSA/WEJSF6ho2zI/AAAAAAAAAME/hKSLu32voiUf_C5XLG_7bGIII0J0aEfpgCLcB/s1600/20140419_STP503.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="360" src="https://2.bp.blogspot.com/-zwauMEbKjSA/WEJSF6ho2zI/AAAAAAAAAME/hKSLu32voiUf_C5XLG_7bGIII0J0aEfpgCLcB/s640/20140419_STP503.jpg" width="640" /></a></div> <div class="MsoNormal" style="margin-left: .5in;"> <b><span style="font-size: 22.0pt; line-height: 115%;"><br /></span></b></div> <div class="MsoNormal"> <span style="font-size: 16.0pt; line-height: 115%;">               According to the recent researches, vascular plants are evolved from mosses like plants.  They were the first group of plant those had chance to grown in larger size in the land due to the presence of vascular system. The vascular system arise from the root system further extends into the stem and leaves. It facilitates the efficient way of water and nutrients transport.<o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 16.0pt; line-height: 115%;">             The division Pterophyta can be distinguished from other plant by a vascular system, a dominant sporophyte and dispersal through spores.  Ferns are also restricted to shady moist environments. Most are terrestrial. Some float on the aquatic bodies. Some grow as epiphytes on the tree trunks and rocks in order to get maximum solar energy for maximum photosynthesis. Most of the ferns are found as herbs and shrubs. Tree plants are rarely found such <i>Angiospetris</i>. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 16.0pt; line-height: 115%;">             The gametophyte is the short lived one of their life cycles. Their sporophytes and gametophytes are <b>heteromorphic </b>which means both of them are differ in morphology.  Both sporophyte and gametophyte are photosynthetic and can live independently. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 16.0pt; line-height: 115%;">             The fern’s sporophyte is much more complex than that of the mosses. The fern sporophyte has vascular tissues. It is well differentiated into the stem, roots and leaves.  The gametophyte is lack of vascular tissues. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 16.0pt; line-height: 115%;">             Fern sporophyte has a horizontal underground stem called rhizome with roots emerging from their sides. Some have aerial stem.  The large compound leaves are referred to as fronds. They usually rise from the tip of the rhizome.  Young leaves are called as fiddle heads which appear as rolled up coils. The fiddle heads unroll and develop into the mature leaves.  Most of the ferns fronds are dissected and feathery<i>. Marselia</i> has fronds which is four clovers. But they also develop form the piddle heads. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 16.0pt; line-height: 115%;">                  Some ferns possess respectively both of photosynthetic vegetative fronds and Non photosynthetic reproductive fronds that appear in brownish color such as <i>Drymyoglossum</i>. Some have elevated fertile fronds and horizontal vegetative fronds such as <i>Anemia</i>. These elevated fronds bear the clusters of sporangia.  Some ferns possess only vegetative fronds but underside of those vegetative fronds bear clusters of sporangia called as <b>sori</b>. It may or not protected by structure called indusum. In <i>Marseilie</i>a, the microsporangia and megasporangia are produced respectively. Those sporangia are enclosed in special bean shaped structure called as <b>sporacarps</b>. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 16.0pt; line-height: 115%;">                  Most Pterophyte are <b>homosporous</b> which produce spores of one size and they result in producing only one gametophyte.  Those homosporous ferns have <b>exosporic</b> <b>development</b> where the gametophyte develops from the outside of the spore wall.  But a significant number of ferns are <b>heterosporous</b> which produce spores of two distinct sizes such tiny microspores and large megaspores.  The microspores produce the male gametophyte and megaspores produce female gametophyte.  Those heterosporous are <b>endosporic development</b> where the gametophyte develops inside the spore wall. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 16.0pt; line-height: 115%;">                      The sporangia in the fertile fronds or sorri have thick walled cells on the one side of the sporangium. It is hygroscopic. The diploid spores mother tissues undergo meiosis and produce haploid spores. . Under dry conditions, those hygroscopic cells contract and cause sporangium to release spores. When favorable conditions receive, spores are germinated and result in producing haploid gametophyte.  These gametophytes are heart shaped and in one cell thickness.  They have rhizoid to anchor themselves to the substrate. <o:p></o:p></span></div> <div class="MsoNormal"> <span style="font-size: 16.0pt; line-height: 115%;">                      The flask shaped archegonia and globular antheridia are produced on either side of the same or different gametophyte.  The sperm found in the antheridia have flagella.  When water is present, sperm swim towards the archegonia through a chemical signal released by the archegonia. After fertilization, the diploid zygote is produced. The zygote is developed into the new haploid sporophyte and completes the life cycle. Although ferns also do not produce seeds, they much advanced form the other seedless vascular plants.  Those vascular plants are considered as <b>polysporangiate</b> which means produce sporangia more than one. <o:p></o:p></span></div> <div class="MsoNormal" style="margin-left: .5in;"> </div> <div class="MsoNormal"> <br /></div>

Seedless non vascular plants (Phylum Pterophyta)

 Seedless non vascular plants             (Phylum Pterophyta)                According to the recent researches, vascular plants a...

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