An investigation into the parameters affecting the stability of Dithane

• Main Author: Williams, Nadia
• Format: Others
• Language: English
• Published: Nelson Mandela Metropolitan University 2007
• Subjects: Fungicides; Dithane
• Online Access: http://hdl.handle.net/10948/645

Plant diseases caused by fungi are the number one cause of crop loss worldwide. The application of a fungicide which is a toxic substance applied either to prevent the growth of, or to kill fungi is one of the methods by which plant diseases are controlled. Ethylenebisdithiocarbamate fungicides are a group of surface acting fungicides which control a broad spectrum of fungi and their associated plant diseases. Mancozeb, also commonly known as Dithane, falls under the polymeric Dithiocarbamate fungicides which have several sites of toxicity to the fungal cell. The use of Mancozeb as a fungicide is increasing worldwide due to the advantages of low acute toxicity, low production and short environmental persistence. However, it has one major disadvantage, namely its lack of oxidative stability under ambient conditions. One of the objectives of this study was to characterize the Dithane samples supplied by Dow AgroSciences in terms of their active ingredient, metal and stabilizer content, and to study the thermal decomposition behaviour of Dithane. An attempt was made to correlate the active ingredient analyses with the TGA and DSC results to establish whether the thermal stability and active ingredient content of Dithane could be simultaneously determined by thermal analysis. This approach offered the attractive advantage of shorter analysis times thus allowing the elimination of the more tedious analytical methods employed by Dow AgroSciences. Furthermore, Fourier Transform infra-red characterization of Dithane samples and metal complexes containing HMT, Mn and/or Zn was carried out in order to identify the presence of functional groups and to gain some insight into the nature of the bonding of HMT, sulfate and water. A study of the nature of the bands in the FTIR spectra of these complexes was able to highlight the nature of the bonding but could not give confirmation of the structures of these complexes. In addition to this, the amount of HMT present in the said complexes was determined by the FTIR using the standard addition method. A final objective of the study was to investigate the reconstitution of Dithane by investigating the influence of the addition order of the various constituents on the stability of the final product. The addition order was found to have a definite influence on the thermal stability of the final product as well as on the percentage of fixed HMT in the product, and the kinetics of the Mn/Zn exchange.