Investigating the causes for poor control of Crassocephalum crepidioides (Thandam pillu) weed by Glyphosate in the Uva region
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Date
2015
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Uva Wellassa University of Sri Lanka
Abstract
Weed management in tea field is great importance among other agronomic practices as weeds are the
number one pest and they can lower the productivity of tea by 10 to 50 percent due to their
competition for light, space, water and nutrients. Various weed management practices are used in tea
cultivation such as manual, mechanical, cultural, chemical, and biological methods. Chemical weed
control is the most convenient and effective methods among the various weed management
techniques available. Unlike manual weeding, chemical weed control minimizes soil erosion and
largely eliminates the loss of plant nutrients, which were carried away in the weeds removed from
the field and less labour required. Other than normal classifications, weeds can be grouped as
common weeds, hard-to-kill weeds and favorable herbs. Among the weeds Thandam pillu was
considered as a common weed, but it is becoming a hard-to-kill weed. It was already become resistant
to Paraquat herbicide and now there are complaints that it is difficult to control even by Glyphosate
herbicide. Recent investigations under up country conditions have shown that such poor control is
attributed to the dosage of Glyphosate applied and the age or growth phase of weeds, (Pre matilake
and Nawarathne, unpublished). Therefore, the objective of the present study was to elucidate the
possible causes of poor control of Thandam pillu weed under Uva region.
Materials and methods
An experiment was carried out at the Uva Wellassa University during July-August 2014.
C.crepidioides weed plants at five different growth phases such as 3-4, 5-6, 7-8, 9-10 and > 10 leaf
phase, were collated from Ury Estate and they were planted randomly on raised beds, (30 plants per
each growth phase) and left for 2 weeks to established. Two Glyphosate (36%) dosages (5 ml/L and
3 ml/L) were sprayed on plants by isolating the plant to prevent contaminations with other plants. An
untreated Control was also maintained. Herbicide application was done as drenching application, by
using hand sprayer during morning. The degree of chlorosis, wilting of leaves, scorching and drying
of leaves and leaf fall occurred at 7, 14 and 21 days after application (DAA) of Glyphosate. Thandam
pillu weed was observed and rated. Dead plant percentage, dry weight of viable plants and recovery
of plants were recorded at 21 DAA.
Results and Discussion
Chlorosis was more prominent at 7 DAA and it occurred at significantly higher rate with Glyphosate
at 5 ml/L than at 3 ml/L at 3-4 and 5-6 leaf growth phases. Leaf wilting was more prominent at 14
and 21 DAA and it occurred at significantly higher rate with Glyphosate at 5 ml/L at all five growth
phases. Scorching and drying of leaves took place at the same rate with both Glyphosate at 5 ml/L
and at 3 ml/L at 3-4, 5-6 and 9-10 leaf growth phases. However, symptoms were more severe with
Glyphosate at 5 ml/L than at 3 ml/L at 7-8 and >10 leaf phases. Leaf fall also occurred more severely
with Glyphosate at 5 ml/L than at 3 ml/L at 7-8 leaf phase. Mean percentage of dead plants of
C.crepidioides was significantly higher with Glyphosate at 5ml/L than that of 3ml/L at all growth
phases. There was no death of the weed after phase 3 onwards with Glyphosate at 3ml/L and at phase
4 and 5 with Glyphosate at 5ml/L.
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Keywords
Agriculture, Export Agriculture, Tea Industrials, Tea Technology, Glyphosate, weed