Journal of Research in Weed Science

Abstract Glyphosate is an effective post emergence herbicide for weed control in tea. However, dose and timing of any new formulation need to be evaluated before being its recommendation to the growers. The weed flora of the experimental field was composed of Ageratum conyzoides (21.9%), Ageratum houstonianum (21.3%), Chromolaena adenophorum (13.0%), Bidens pilosa (9.6%), Lantana camara (6.2%), Cynodon dactylon (6.0%), Fragaria vesca (5.6%), Imperata cylindrica (5.2%), Polygonum alatum (5.1%) and Erigeron canadensis (5.1%). The new formulation glyphosate 71% SG was found to be comparable to the existing formulation glyphosate 41% SL against Ageratum conyzoides, A. houstonianum, Chromolaena adenophora, Bidens pilosa, Fragaria vesca, Polygonum alatum, Erigeron canadensis, Imperata cylindrica and Cynodon dactylon in reducing their population upto 120 days after application (DAA). Glyphosate 71% SG did not show any toxic symptoms on tea crop and tea leaf yield was similar as under standard formulation used in the present study. Glyphosate 71% SG (ammonium salt) sprayed at 6 kg/ha gave highest tea leaf yield (1940 kg/ha) which was statistically similar to the Glyphosate 71% SG (ammonium salt) applied at the rate of 3 kg/ha (1895 kg/ha). It was also comparable to the market sample. Uncontrolled growth of weeds even for a one season reduced tea leaf yield by 48.5%. The bulk density, water holding capacity, moisture content, soil pH, electrical conductivity, available NPK and organic C were not influenced significantly at harvest. The test herbicide glyphosate 71% SG and the market sample glyphosate 41% SL had increased the population of total bacteria, fungi and actinomycetes at harvest over their initial population. However, there was a slight decrease in the population of this microflora immediately after the application of herbicide not due to the herbicide but owing to seasonal variation as the differences between treatments were not significant.

Abstract The bio-efficiency of imazethapyr and its ready mix combination products with pendimethalin and imazamox against weeds, their effect on growth, yield and phytotoxic effects on black gram and residual effect on succeeding mustard crop were studied during 2013-14. Significantly lower weed count and dry weight was recorded with application of imazethapyr + pendimethalin (pre-mix) at 800 g/ha, pendimethalin at 1000 g/ha and imazethapyr + pendimethalin (pre-mix) at 900 g/ha. Imazethapyr + pendimethalin (pre-mix) 1000 g/ha and 800 g/ha, pendemethlin 1000 g/ha and imazethapyr 50 and 70 g/ha (pre emergence) behaving statistically similar with pendimethalin 1000 g/ha (pre emergence) and hand weeding at 20 and 40 days after sowing resulted in significantly higher seed yield of black gram. Seed yield of blackgram was negatively associated with total weed count and weed dry weight (P≤0.01). With every one weed increase per square meter, the blackgram seed yield was expected to reduce by 16.8 kg/ha. Net returns, B:C and net returns over weedy check were highest under imazethapyr + pendimethalin 900 g/ha. The economic threshold levels i.e. No m^-2 and g m^-2 with the weed management practices studied varied between 1.7 – 18.0 m^-2 and 1.0-10.0 g m^-2. Imezethapyr + pendimethalin 1000 g/ha and imazethapyr + imazamox 50 g/ha had lowest weed persistence index (WPI). Imazethapyr + pendimethalin 900 g/ha resulted in highest crop resistance index. Weed management index (WMI), Agronomic management index (AMI), and Integrated weed management index (IWMI) were highest following imazethapyr 40 g/ha. Overall impact index (Ii) was highest under imazethapyr 50 g/ha followed by imazethapyr + pendimethalin 900 g/ha, imazethapyr + pendimethalin 1000 g/ha and pendimethalin 1000 g/ha. Weed index (WI) indicated 70.8% loss in yield of blackgram. The residual effects of herbicide treatments on succeeding mustard crop were not observed.