**4. Allelochemicals release and control weed**

#### **4.1 Concept and production of allelopathy**

Allelopathy is said to have any effect that plants have on the production of other chemical compounds released into the environment (RICE, 1984). Plants are able to produce chemicals with properties that affect beneficial or harmful in other plant species phenomenon called allelopathy, which is of Greek origin meaning *allelon* (from one to another) and *pathos* (suffering) (MOLISCH, 1937). Currently, this conceptual definition has become broader, expanding into the animal kingdom, since the interaction can occur between them and the plants and between animals and plants (GARDEN OF FLOWERS, 2001).

The chemicals responsible for allelopathy are called allelochemicals, whose function is primarily protective (SORIANO, 2001). The natural compounds with phytotoxic properties may have a high potential to control weeds (SOUZA-FILHO, 2006). According to MORALES et al. (2007), these compounds tend to have low toxicity to non-target organisms of control, as a potential source in the discovery of new molecules of herbicides less harmful to the ecosystem.

Unlike the common occurrence of compounds with allelopathic properties in higher plants, the amount and composition of these may vary depending on the species, age of the organ of the plant, temperature, light intensity, nutrient availability, microbial activity of the rhizosphere and composition of the soil in which they are the roots (PUTNAM, 1985; EINHELLIG and LEATHER, 1988).

Many are organic compounds produced by higher plants or microorganisms that have been identified as allelochemicals, which are: terpenes, steroids, organic acids, soluble in water, aliphatic aldehydes, ketones, long chain fatty acids, polyacetylenes, naphthoquinones, anthraquinones and complex quinones, originate from the mevalonate metabolic pathway of acetate (REZENDE and PINTO, 2003). Already the simple phenols, benzoic acids and derivatives, cinnamic acids and derivatives, coumarins, amino acids, polypeptides and sulfides and glycosides, alkaloids, cianidrina, flavonoids, and purine nucleoside derivatives, quinones and hydrolysable and condensed tannins are derived from the acid metabolic pathway shikimic (REZENDE and PINTO, 2003).

The humic acids in general allow a better exchange of chemicals, so that some authors suggest a decrease in those with the maintenance of efficacy was observed that the FOLONI and SOUZA (2010) working with cane sugar, concluding in his work that the use of humic acid in doses of 3.0 and 6.0 L ha -1 did not cause phytotoxicity apparent effect on the culture of sugar cane plant. The addition of the use of humic acid with Dual Gold in different combinations, even with dose reduction of 25% allowed an excellent control of the main

In assessing the remobilization of bound residues of 14C-anilazina fulvic acids in two soils of Germany, LAVORENTI et al. (1998) observed a small percentage of this waste in the humic and humin fractions and that the microorganisms were stimulated by applying the treatments corn stover (1.5 g 100 g -1 dry soil) and glucose + peptone (0.2 g + 0.2 g 100 g-1 dry

Allelopathy is said to have any effect that plants have on the production of other chemical compounds released into the environment (RICE, 1984). Plants are able to produce chemicals with properties that affect beneficial or harmful in other plant species phenomenon called allelopathy, which is of Greek origin meaning *allelon* (from one to another) and *pathos* (suffering) (MOLISCH, 1937). Currently, this conceptual definition has become broader, expanding into the animal kingdom, since the interaction can occur between them

The chemicals responsible for allelopathy are called allelochemicals, whose function is primarily protective (SORIANO, 2001). The natural compounds with phytotoxic properties may have a high potential to control weeds (SOUZA-FILHO, 2006). According to MORALES et al. (2007), these compounds tend to have low toxicity to non-target organisms of control, as a potential source in the discovery of new molecules of herbicides less harmful to the

Unlike the common occurrence of compounds with allelopathic properties in higher plants, the amount and composition of these may vary depending on the species, age of the organ of the plant, temperature, light intensity, nutrient availability, microbial activity of the rhizosphere and composition of the soil in which they are the roots (PUTNAM, 1985;

Many are organic compounds produced by higher plants or microorganisms that have been identified as allelochemicals, which are: terpenes, steroids, organic acids, soluble in water, aliphatic aldehydes, ketones, long chain fatty acids, polyacetylenes, naphthoquinones, anthraquinones and complex quinones, originate from the mevalonate metabolic pathway of acetate (REZENDE and PINTO, 2003). Already the simple phenols, benzoic acids and derivatives, cinnamic acids and derivatives, coumarins, amino acids, polypeptides and sulfides and glycosides, alkaloids, cianidrina, flavonoids, and purine nucleoside derivatives, quinones and hydrolysable and condensed tannins are derived from the acid metabolic

and the plants and between animals and plants (GARDEN OF FLOWERS, 2001).

**3.2 Humic substances on the recommendation of herbicides** 

**4. Allelochemicals release and control weed** 

**4.1 Concept and production of allelopathy** 

soil).

ecosystem.

EINHELLIG and LEATHER, 1988).

pathway shikimic (REZENDE and PINTO, 2003).

weeds present, equaling or surpassing traditional treatments until 120 DAT.

These compounds can be released from allelopathic plants through leaching and volatilization, root exudation and decomposition of plant residues (WEIR et al., 2004). A large number of allelopathic compounds such as oxalic acid, the amygdalin, coumarin and transcinâmico acid, are released into the rhizosphere and can act directly or indirectly in plant-plant interactions and the action of microorganisms.

The allelopathic effects may occur in the forms of auto toxicity and hetero toxicity (MILLER, 1996). The autotoxicidade occurs when the plant produces toxic substances that inhibit seed germination and growth of plants of the same species. Research has shown that alfalfa plants contain water-soluble phytotoxic compounds that are released into the soil environment by means of fresh leaves, stems and crown tissues as well as dry material, decaying roots and seeds (HALL and HENDERLONG, 1989). The phytotoxic hetero toxicity occurs when substances are released by leaching and root exudation and decomposition of waste in any type of plant on seed germination and growth of other plants (NUÑEZ et al., 2006). This second form is more potential to be explored by science, as a subsidy for the control of weeds in organic farming systems, or even as a tool to reduce costs with herbicides in conventional systems management.

#### **4.2 Mode of action of allelochemicals**

The action of allelochemicals and modification involves inhibition of growth or development of plants. According to SEIGLER (1996), the allelochemicals can be selective in their actions and plants can be selective in their response, which is why it is difficult to clarify the mode of action of these compounds. Several mechanisms of action of allelochemicals can affect the processes of respiration, photosynthesis, enzyme activity, water relations, stomatal opening, level of hormones, mineral availability, division and cell elongation, structure and permeability of membranes and cell wall (REZENDe et al. 2003). The same authors reported that many of these processes occur as a result of oxidative stress. One of the many effects of allelochemicals in plants is to control the production and accumulation of reactive oxygen species (ROS), which accumulates in cells in response to the allelochemical, thereby being responsible for damaging the cells causing their death (TESTA, 1995 ). Among them, blocking chain that carries electrons, where electrons are free and easily react with O2 to form superoxide. Another known mechanism in the formation of ROS is the activity of allelochemicals on the NADPH oxidase, an enzyme that transfers electrons from the NDPH and donates to an acceptor (O2) forming superoxide (FOREMAN et al., 2003).

Some allelochemicals rapidly depolarize cell membranes, increasing permeability and inducing lipid peroxidation, causing a generalized cell disorder that leads to cell death (YU et al., 2003).

#### **4.3 Weed control by allelopathic effect**

Seeds of *Coronilla L varies.* showed reduced germination rate when exposed to aqueous extracts of *Eucalyptus camaldulensis* and *Juglans regia* (ISFAHAN and SHARIAT, 2007). Soils planted with species *E.grandis, E.* and *E. urophylla grandis x urophylla* contains water-soluble phenolic compounds that inhibit the germination and early growth of black beans *(Phaseolus vulgar)* (ESPINOSA-GARCIA et al., 2008). According BURGOS et al. (2004), the

Weed Population Dynamics 343

CHEFETZ, B.; BILKIS, Y.I.; POLUBESOVA, T. Sorption-desorption behavior of triazine and

CRUTCHFIELD, D.A.; WICKS, G.A.; BURNSIDE, O.C. Effect of winter wheat (*Triticum aestivum*) straw mulch level on weeds control. *Weed Science*, v.34, p.110-114, 1985. CZARNOTA, N.A.; RIMANDO, A.M. Evaluation of root exudates of seven sorghum accessions. *Journal of Chemical Ecology*, v. 29, n. 9, p. 2073-2083, 2003. DERPSCH, R.; SIDIRAS, N.; HEINZMANN, F.X. Manejo do solo com coberturas verdes de

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DURIGAN, J. C.; ALMEIDA, F. L. S. *Noções sobre alelopatia*. Jaboticabal: FUNEP, 1993. 28 p. EINHELLIG, F.A. AND G.R. LEATHER. 1988. Potetials for exploiting allelopathy to enhance

ESPINOSA-GARCIA, F.J.; MARTINEZ, H.E.; QUIROZ, F.A. 2008. Allelopathic potential of

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GAZZIERO, D.L.P.; VARGAS, L.; ROMAN, E.S. (2004). Manejo e controle de plantas

ISFAHAN, M.N. AND M. SHARIATI. 2007. The effect os some allelochemicals on seed

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allelochemicals produced by *Secale cereale L.* reduces root growth of *Cucumis sativus L.* causing changes in cellular structures of the roots. Thus, a large part of allelochemicals acts on oxidative stress by producing reactive oxygen species, which act directly or as flags to the processes of cell degradation, thus preventing the germination and early development, as well as physiological processes of plants.

Another effective technique for controlling weeds, mainly due to physical and allelopathic effects is the use of green manure. FONTANÉTTI et al. (2004) observed that species velvetbean *(Stizolobium aterrimum)* and pork-bean *(Canavalia ensiformis)* significantly reduced the number of nutsedge when incorporated into the soil before planting romaine lettuce and cabbage. Already CAVA et al. (2008) found that plants such as *C. juncea, C. spectabilis, M. aterrima* and *M. pruriens* have high competitive capacity by reducing the production of dry mass and number of weeds. SEVERINO and CHRISTOFFOLETI (2001) found that the use of green manures *Arachis pintoi, C. juncea* and *Cajanus cajan* have significantly reduced the seed bank of species *Brachiaria decumbens, Panicum maximum* and *Bidens pilosa.*

Thus, it is clear that the population dynamics of weed species is a function not only of the main crop, soil and planting season, but also because of the tillage system, the quantity and quality of dry matter present in the soil surface. This is due to the fact that each species used in land cover has production of metabolites that interfere with specific control of weeds. The association provides interaction with herbicides and microorganisms in the soil fauna, as well as decreasing the dose of herbicides due to the increased amount of straw on the soil surface.

#### **5. References**


allelochemicals produced by *Secale cereale L.* reduces root growth of *Cucumis sativus L.* causing changes in cellular structures of the roots. Thus, a large part of allelochemicals acts on oxidative stress by producing reactive oxygen species, which act directly or as flags to the processes of cell degradation, thus preventing the germination and early

Another effective technique for controlling weeds, mainly due to physical and allelopathic effects is the use of green manure. FONTANÉTTI et al. (2004) observed that species velvetbean *(Stizolobium aterrimum)* and pork-bean *(Canavalia ensiformis)* significantly reduced the number of nutsedge when incorporated into the soil before planting romaine lettuce and cabbage. Already CAVA et al. (2008) found that plants such as *C. juncea, C. spectabilis, M. aterrima* and *M. pruriens* have high competitive capacity by reducing the production of dry mass and number of weeds. SEVERINO and CHRISTOFFOLETI (2001) found that the use of green manures *Arachis pintoi, C. juncea* and *Cajanus cajan* have significantly reduced the seed bank of species *Brachiaria decumbens, Panicum* 

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**19** 

*Poland* 

*Bartman W., Trost B. M.* 

**Ecological Production Technology** 

**of Phenoxyacetic Herbicides MCPA** 

Wiesław Moszczyński and Arkadiusz Białek *The Institute of Industrial Organic Chemistry,* 

*"Selectivity is a major goal in modern synthetic chemistry"* 

**and 2,4-D in the Highest World Standard** 

Herbicides MCPA (4-chloro-2-metylphenoxyacetic acid) and 2,4-D (2,4-dichlorophenoxyacetic acid), which belong to the group of chlorophenoxyacetic acids, have been produced in Poland since the break of the sixties in the scale of many thousands of tons per year, which constitutes 5-7% of the world's production. Acids and their salts are exported to all continents. An advantage of herbicides within this group is their harmlessness for man and environment in doses used in agriculture. The condition is the high content and purity of the active substance in utility preparations. Unfortunately, classic technologies based on the reaction of phenols chlorination or their derivatives used until today all over the world do not ensure high purity, and significant quantities of highly toxical chloroorganic waste compounds originate in the production process. The main cause lies in the low selectivity of the reaction of chlorination of phenols' aromatic ring. Numerous producers enrich the purity of chlorophenols with the method of rectification. As our research has shown, in the process of rectification and while burning post-rectification wastes, dioxines and

Below we present research conducted in the Institute of Industrial Organic Chemistry (IPO) in Warsaw with strict cooperation with production plants "Rokita Agro" in Brzeg Dolny and "Organika Sarzyna" in Nowa Sarzyna over the development of technologies of chlorophenoxyacetic herbicides. Commonly used "classical" technologies of production of MCPA and 2,4-D are based on two subsequent reactions – chlorination of phenol or 2 methylphenol and the reaction of the obtained chlorophenol with chloroacetic acid (MCAA), commonly called condensation. The first stage – chlorination reaction – is critical for the nature of the entire reaction, i.e. the number of operations, selection of equipment, purification methods, wastes. Electrophilic reaction of chlorination of aromatic phenol ring is non-selective. Isomers and polychlorinated compounds are always originated. In order to increase the selectivity of reaction and the purity of the the final product, various technologies of chlorination and purification of chlorophenols are used all over the world,

**1. Introduction** 

dibenzofurans can originate.

