Investigations on new fungicidal systems for control of bark rot on Hevea brasiliensis

Abstract

The efficacy of Bark Rot fungicides is significantly impared by frequent rains. The present investigation was therefore undertaken to examine the possibility of increasing the efficacy of panel fungicides by incorporating them in rubber latex. Several didithiocarbamates containing metal ions, chemicals such as zinc oxide and formaldehyde and fungicides recommended for Bark Rot control were used singly or in combination, in in vitro trials. Zinc oxide and Zinc dithiocarbamates were of limited use, while others gave satisfactory results. The influence of rubber serum, on the activity of the chemicals and fungicides was then examined. It was shown that all the materials tested except Ziram inhibited te growth of the fungus. Prevulcanised latex was not found to be suitable as an adjuvant under laboratory conditions. However, satisfactory result were obtained when fungicides were incorporated into high ammonia field latex and high and low-ammonia centrifuged latex. The use of preserved latex as an adjuvant with Antimucin and Thiram (TMTD), singly or in combination, was investigated under field conditions. Infection occurred on tapping panels which were inoculateed after removal of scrap, although fungicides were applied prior to inoculation. Disease also occurred on panels, when the inoculum was removed a week after inoculation, but its spread was arrested when fungicides were applied, indicating that continued applications of fungicides could limit the spread of the disease. Panels which were tapped and protected with Antimucin at the time of collection of latex, when inoculated 4 hours later, without removal of scrap, showed less infection. The significance of these findings, in relation to the control of Bark Rot and the influence of these fungicides on the yield are discussed.