Controlled release herbicides

McCormick, C.L. and M.M. Fooladi, "Synthesis, Characterization, and Release Mechanisms of Polymers Containing Pendant Herbicides," Controlled Release Pesticides, ACS Symposium Series 53, 112-125, H.B. Scher, ed., Washington, D.C., 1977. 

Dextran mixed with PVP and poly(vinyl acetate) was crosslinked with epichlorohydrin to fonn beads containing herbicides. Controlled release of herbicnles. Rehab et at., 1991... 

The concept of fibrous polymer formulations was extended to the delivery of aquatic herbicides (56). Several herbicides including Diquat, Fluridone, and Endothal were spun into biodegradable poly-caprolactone. Monolithic fibers and a modified monolithic system were produced with levels of herbicide from 5 to 60% by weight. Laboratory and field trials showed efficacious delivery of the active agent. Fibers provided both targeted localized delivery and controlled release of the herbicide to the aquatic weed. 

B. M., Price, M. W., and Stoner, W. C., Jr., Polymeric-pellet delivery systems for controlled release of aquatic herbicides, Toronto Controlled Release Society, Proc. 14th Int. Symp. Control. Rel. Bioact. Materials, 291-292, 1987. 

Chemical-based products cover a broad spectrum of materials and forms, ranging from molecules to appliances. Table 16.1-1 shows the various product functional forms, along with examples in major application areas. Examples highlighted in italic are those discussed in this book. Most small molecules such as BTX (benzene-toluene-xyxlene) are sold to chemical and allied products industries while a limited number such as refrigerants and solvents are for sale in the consumer market. In contrast, multicomponent liquid mixtures such as liquid shampoo, semi-solids such as cream and paste, and structured solids such as controlled release herbicide are often sold directly to the consumers. Business-to-consumer sale is even more prevalent for ready-to-use devices and appliances such as diagnostic kits, drinking water filters and air cleaners. 

A controlled release herbicide based on Metribuzin attached to poly(vinyl alcohol) has been reported via an isocyanate reaction as shown in Equation 18. Data on the release rate has been published (54). 

McCormick, C.L., D.K. Lichatowich, and M.M. Fooladi, "Controlled Activity Pendant Herbicide Systems Utilizing Chitin and Other Biodegradable Polymers," Proceedings of the 5th International Symposium on Controlled Release of Bioactive Materials, pp. 3.6-3.17, Gaithersburg, MD (1978). 

The polystyrene latexes produced from concentrated emulsions have been used as carriers for the controlled release of herbicides [160], The release of 2-(2,4-dichlorophenoxy) propionic acid (2,4-DP) was found to depend on the water concentration, increasing with increasing dilution of the latex. High conversion to polymer was required to prevent a large initial release of herbicide on dilution however, a significant initial burst was still observed at almost complete conversion. This was reportedly due to dissolution of 2,4-DP at, or near, the surface of the latex particles. 

Application of several types of lignin sulfonates as carriers in connection with reactive herbicides (21-23) permits the development of effective controlled release (CR) preparations. The properties of chemically bound lignin 2,4-D-based herbicides are summarized in Table XI. 

It can be concluded that lignin sulfonates modified by reaction with herbicide functionality (21-23) can be used as potential carriers for controlled release herbicides. This application of lignin sulfonates offers several advantages both for agriculture and for the environment. 

Substances other than enzymes can be immobilized. Examples include the fixing of heparin on polytetrafluoroethylene with the aid of PEI (424), the controlled release of pesticides which are bound to PEI (425), and the inhibition of herbicide suspensions by addition of PEI (426). The uptake of anionic dyes by fabric or paper is improved if the paper is first catonized with PEI (427). In addition, PEI is able to absorb odorizing substances such as fatty acids and aldehydes. Because of its high molecular weight, PEI can be used in cosmetics and body care products, as well as in industrial elimination of odors, such as the improvement of ambient air quality in sewage treatment plants (428). 

Boydston, R.A. (1992). Controlled release starch granule formulations reduce herbicide leaching in soil columns. Weed Technol., 6 317-321. 

Riggle, B.D. and D. Penner (1988). Controlled release of three herbicides with the kraft lignin PC940C. Weed Sci., 36 131-136. 

The main use of PVC is for intravenous bags. However, PVC has been used in the controlled release of volatile insecticides, herbicides, pheromones, and perfumes by diffusion through a PVC membrane of multilaminated stripes. A monolithic matrix device of PVC can be prepared by mixing PVC particles with a suitable plasticizer and an active agent, followed by heating of the mixture in a mold. A solid PVC matrix is obtained from the subsequent cooling. 

Piletska, E. V. Turner, N. W. Turner, A. P. F. Piletsky, S. A, Controlled release of the herbicide simazine from computationally designed molecularly imprinted polymers, J. Controlled Release. 2005, 108, 132-139... 

The controlled release of various types of herbicides have been studied by many workers and has been summarized elsewhere (4-6, 23). Less Is known, however, about the controlled release of herbicides for land plants than for aquatic plants. Previous studies by other research groups have reported that Isocyanate modified polymers, made from chltln, cellulose or poly(vlnyl alcohol), hydrolyze slowly In aqueous media to release the corresponding aniline derivative (17,24,25). No data appears to be currently available on how effective these agents are as herbicides. 

Controlled release of agrochemicals (e.g., by hydrolysis of a polymeric ester) can offer the advantages of constant level, smaller dose, reduced evaporation loss, lower toxicity, longer life, decreased environmental pollution, and reduced effect on nontarget species by wind or runoff.20 Systemic pesticides are preferred. This ensures protection of the growing tip of the plant. For weed killers, this means that it is not necessary to hit every leaf of the plant with the herbicide. Pesticides are often applied on a spray schedule according to the calendar as a prophylactic measure. Chemical pesticides are used 98% of the time. 

At the time of writing, the applications of biodegradable polymers are confined mostly to the field of agriculture, where they are used in products with limited lifetimes, such as mulch films and pellets for the controlled release of herbicides. The synthetic polyesters used in medical applications, principally polylactide and poly(lactide-co-glycolide), while claimed to be biodegradable, are degraded in the body mainly, if not entirely, by chemical hydrolysis. There is little evidence that the hydrolysis of these polyesters of a-hydroxyacids can be catalyzed by hydrolase or depolymerase enzymes. 

In the beginning, spheronization had been primarily used in the pharmaceutical industry as a final forming method for formulations with high active loading. A spherical particle was needed for coating with a thin polymeric material for controlled release (see also Section 10.1). Today, spheronization is also applied for animal medicines, herbicides, enzymes, specialty fertilizers, advanced ceramics, and many more. 

A number of natural biopolymers containing pesticide active groups have been in the market for the purpose of developing ideal controlled release formulations for fungicides and herbicides. These biopolymers have been derived by natural exudation. Several factors appear to be important in governing the rates of release of active moieties. These factors include environmental conditions as well as the effects of the biopolymers compositions, properties and chemical structures, and the simulated conditions necessary to prolong the activity under suboptimal conditions such as the pH and temperature. 

Some patents refer to the controlled release of certain pesticides [58, 59]. Matolcsi et al. [60] used j8-CyD to prepare inclusion compounds with benzenesul-fonylurea derivatives with herbicidal or plant growth regulator properties [61], obtaining a prolonged controlled release of the active ingredient. Ikeuchi et al. [62] prepared inclusion complexes of triazole derivatives which presented potent insecticidal activities at low concentrations for an extended period. 

Degradable materials also offer new perspectives in agriculture (e.g., the controlled release of fertilisers, insecticides and herbicides)... 

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