Effect of Post-Emergence Application of Dichlorophenoxy Acetic Acid (2,4-D) Herbicide on Growth and Development of Three Weeds Associated with Maize Plant Growth
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520 Current Science International 3(4): 520-525, 2014 ISSN: 2077-4435 Effect of Post-emergence Application of Dichlorophenoxy acetic acid (2,4-D) Herbicide on Growth and Development of three Weeds Associated with Maize plant growth Hanan M. Abou El-ghit Botany and Microbiology department, Science Faculty, Helwan University, Cairo, Egypt. ABSTRACT Post emergence application of 2,4-Dichlorophenoxyacetic acid (2,4-D) as a herbicide even at low concentrations showed an effective control on three weeds (slender amaranth, goosefoot and prickly burweed) associated with maize growth. 2,4-D was applied at 0.0, 125, 250, 500 and 1000 ppm. 250 ppm 2,4-D treatment significantly decreased numbers and fresh weights of the three weeds by 50% approximately. At 1000 ppm 2,4- D, there were sever reductions in weeds numbers, fresh weights and photosynthetic pigments contents of the three weeds. Maize was undamaged by any tested 2,4-D treatment. Fresh weights and photosynthetic pigments contents of maize were favored significantly after application of 2,4-D on the associated weeds at all tested rates. Key words: Maize, Weeds, Chemical control, Herbicides, Phenoxy herbicides, 2,4-Dichlorophenoxy acetic acid (2,4- D), Auxins. Introduction Maize (Zea mays L.) is the second most important cereal crop in Egypt in terms of total food production. It is grown for fodder as well as for grain. The grains of maize are used in a variety of ways by the human beings. Weeds are a major problem in crop production and drastically decrease crop yield. Therefore, weed control is an important management practice for maize production that should be carried out to ensure optimum grain yield. Yield losses due to weeds have been reported up to 35 % (Oerke, 2005; Dangwal, et al. 2010). Thus, in maize production, it is necessary to undertake control of weeds which cause losses of maize grain yield. The use of herbicides may reduce such losses, as herbicides may reduce the weed infestation provided that the herbicide-treated weeds are not herbicide resistant. Prior to the widespread use of chemical herbicides, cultural controls, such as altering soil pH, salinity or fertility levels were used to control weeds. Weed is a common term for any wild plant, particularly an undesired plant, growing in cultivated ground, where it competes with crop plants for soil nutrients, light and water. Slender amaranth (Amaranthus viridis), goosefoot (Chenopodium album) and prickly burweed (Xanthium spinosum) are troublesome broad leaved weeds associate with maize growth (Malik et al. 2006). Amaranthus viridis is a cosmopolitan weed belong to family amaranthaceae, Chenopodium album is a fast-growing weed belong to family chenopodiaceae , whereas .Xanthium spinosum is a noxious weed in asteraceae family. Most herbicides are applied as water-based sprays using ground equipment. Some herbicides are synthetic mimics of natural plant hormones. Herbicides are weed killers used to kill unwanted plants (Kellogg et al., 2000). Malik et al. (2006) reported that herbicides proved effective in controlling weeds and produced relatively more weight of cobs of maize, number of grains/ cob, grain weight, biological yield and grain yield. Selective herbicides kill specific targets, while leaving the desired crop relatively unharmed. Herbicide use has undoubtedly contributed to crop yield increases and the efficiency of production (Andrew, 2012). Some substantial benefits can be gained through the use of herbicides to manage unwanted vegetation. If herbicides are not used properly, damage may be caused to crop plants, especially if too large a dose is used, or if spraying occurs during a time when the crop species is sensitive to the herbicide. Unintended but economically important damage to crop plants is sometimes a consequence of the inappropriate use of herbicides (Robert, 1941 and Mehmeti, 2004). Herbicides have different modes of actions on enzymes (catalysts of biological reactions), this means that the target enzymes may no longer function properly, or at all. Herbicide distort enzymes molecules in some way, so component chemicals for the reaction accumulate and may be directly or indirectly damaging. Absence of the reaction’s products will restrict growth, either through starvation of key building blocks or because the reaction makes chemicals which normally protect the plant (Santra and Baumann, 2008). Corresponding Author: Hanan. M. Abo El-ghit, Botany and Microbiology Department, Science Faculty, Helwan University, Cairo, Egypt. E-mail: [email protected] 521 Curr. Sci. Int. 3(4): 520-525, 2014 Auxin is a plant growth regulator that controls cell enlargement, division and plant development through the plant life cycle. Over decades, the so-called auxin herbicides had resisted all efforts to elucidate their molecular interactions and the biochemical and physiological basis of their phytotoxicity (Cobb, 1992). Auxin herbicides started a new era of weed control in modern crop production due to their systemic mobility in the plant and to their selective action, preferentially against dicot weeds in cereal crops ( Cobb, 1992 and Grossmann, 2007). Auxin herbicides mimic the action of the main auxin, indole-3-acetic acid (IAA) in higher plants (Cobb, 1992). However, they are long-lasting, particularly due to their higher stability in the plant, and, therefore, more effective than IAA. Auxins stimulate a variety of growth and developmental processes when present at low concentrations at the cellular sites of action. However, with increasing concentration and auxin activity in the tissue, growth is disturbed and the plant is lethally damaged (Grossmann, 2003). At the present time, nobody really knows precisely how the auxin-like herbicides kill susceptible plants. As with most effects of plant hormones, it probably has a lot to do with the plant species. In general, grasses are much less sensitive to synthetic auxin herbicides than are dicots. That is, a much higher threshold level of auxin- based herbicide is required to elicit physiological responses in grasses versus the so-called “broadleaf” plants. So, for example, at the doses used to kill dandelions, grasses are largely unaffected (Cobb, 1992 and Grossmann 2003). Auxin-based herbicides are referred to as “selective” herbicides because they kill so-called “broadleaf” plants (dicots) but not grasses, hence, that’s why they’re popular herbicides with growers of lawns. Phenoxy herbicides are structural and functional analogs of the natural auxin indole-3-acetic acid (IAA). Although they both look and act like auxins, plants cannot metabolize these phenoxy herbicides as they can with the natural auxin (IAA). Phenoxy herbicides work by binding to some or all of the same sites in the plant cells as naturally occurring IAA. While naturally occurring IAA concentrations in the cell are highly regulated, when phenoxy herbicides are applied, plant growth becomes deregulated. This deregulation causes twisting, thickening and elongation of leaves and stems and eventually leads to plant death as the plant cannot mobilize reserves, repair or function properly (Song, 2014). The phytotoxic effect of phenoxy herbicides is basically caused by high concentrations of biosynthesized abscisic acid (ABA) which may lead to stomatal closure and inhibition of transpiration and CO2 assimilation (Grossman, 2000). These effects are followed by foliar senescence with chloroplast damage and by the destruction of membrane and vascular system integrity and plant death (Fedtke and Duke, 2005). 2,4-D is a synthetic auxin, it is a member of the phenoxy family of herbicides. It is absorbed through the leaves and is translocated to the meristems of the plant. Uncontrolled, unsustainable growth ensues, causing stem curl-over, leaf withering, and eventual plant death. 2,4-D mimics the plant hormone auxin and sets off a complex series of events involving two other plant hormones that eventually lead to the death of susceptible plants. At hormonal levels, auxins affect plants but not people (Grossmann, 2007). Spraying 2,4-D on susceptible plants kill them and it simply confuses the plant to death (Grossmann, 2007 and Song, 2014). 2,4-D is a common systemic herbicide used in the control of broadleaf weeds. It is one of the most widely used herbicides in the world. It was known to be a selective post emergence herbicide primarily used to weed control. The first publication of 2,4-D's herbicidal activity was reported by Hamner and Tukey (1944) and Quastel (1949). It revolutionized weed control, as it was the first compound that, at low doses, could selectively control dicots broadleaf plants, but not most monocots narrow leaf crops like wheat, maize (corn), rice, and similar cereal grass crops (Andrew et al., 2010). 2,4-D generally has low toxicity for humans (Aylward, 2010). Methodology A pot experiment was carried out to examine the effect of foliar application of 2,4-Dichlorophenoxyacetic acid (2,4-D) as a herbicide on the growth of three weeds (slender amaranth, goosefoot and prickly burweed) which grow associated with maize plant. 2,4-D was applied at different concentrations (0.0, 125, 250, 500 and 1000 ppm). Maize and weeds were grown in pots (40 cm in diameter) of 15 kg of clay loamy soil. Fifteen seeds of each weed were sown with ten seeds of maize. 2,4-D was sprayed on weeds with a hand sprayer after 2 weeks of sowing and repeated after one week. Precautions were taken to avoid damage of maize plant. There were three replicates of each treatment of 2,4-D. Irrigation was done regularly to maintain soil field capacity. The effect of 2,4-D herbicide was measured after five weeks of sowing by counting of slender amaranth, goosefoot and prickly burweed numbers ( plants/pot) and estimation of fresh weights of each weed (g/ 3plants). Also, fresh weight (g) of maize plant was estimated after 2,4-D application on the associated weeds. Chlorophyll a, b and carotenoids contents in the fresh leaves of weeds and maize (mg/g.