Abstract:
The usage of agro chemicals on food crops is getting restricted day by day with the sanctions set by the institutes
devoted in food security, mainly due to the disclosure of their harmful residual effects on human health. Thus,
several Commercial Tea Plantation companies have voluntarily suspended the use of many Herbicides on Tea under
their charge, which are still permitted to use in Sri Lanka. Intense emergence of Herbicide tolerant weed species on
treated areas was noted in the mean time, although this crucial factor had been remained un-noticed as a result of
frequent manual weeding under taken by the Tea estates under various other accounts such as plucking, fertilizer
application, mossing and ferning green manure etc. Therefore, an investigation was carried out to ascertain the
affectivity of Herbicides recommended for Commercial Tea Plantations, over a period of 24 months in
Hapugastenne Tea Garden, Maskeliya, since year 2012 at five different elevations, with five replicates set at each
elevation. Results show that over 20 weed species out of 23 acutely problematic weeds which cause great damage to
Tea crop, are entirely tolerant to Diurone, Paraquat and Glyphosate and cannot be controlled by using said
Herbicides. It was further revealed that such weed species have the ability to turn a Tea Plantation into a totally
unproductive and economically non-viable unit within a time period of one to two years depending on the herbicide
tolerant weed species present. These weeds are capable of suppressing the growth of the Tea bushes by making them
stunted in growth with poor bush frames, turn the foliage yellowish and induce defoliation, unless they were
removed completely by manual uprooting
