Abstract:
In this research, a series of glasshouse and field
trials were carried out to re-evaluate the chemical control
of torpedograss (Panicum repens l.), with an intention to
reduce the cost involved, either by improving the activity of
the genera 11 y recommended he rb i c ide, glyphosate, with
modified spray formulations, or by introducing new generation
novel systemic 'graminicides', sethoxydim, f1uazifop-P or
ha1oxyfop-methy1.
G 1yphosate" sethoxydim, ha10xyfop-methy1 and
f1uazifop-P applied as foliar sprays were evaluated for
torpedograss control under both glasshouse and field
conditions. In general, glyphosate and sethoxydim at the
rates of 2.0 and 4.0 Kg/ha achieved superior control of the
grass, suppress ing 90-95% regrowth 30 days after treatment
and achieving 95-100% rhizome bud ki 11. The performance of
f1uazifop and ha1oxyfop , as measured by regrowth suppression
was significantly less at these rates, although the latter
two herbicides also caused 90-95% kill of rhizome buds. Rates
below 1.0 Kg/ha of all four herbicides gave insufficient
regrowth suppression and bud ki11 and could not adequately
cont ro 1 we 11 estab 1 i shed matu re plants. Of the herbicides
tested ha10xyfop-methy1 showed the least phytotoxic effects
on the grass.
The effect of the quality of water used as the
carrier volume had a significant effect on the performance of
glyphosate. G1yphosate activity was enhanced greatly when
de-ionized water was used instead of 'well' water to prepare
the spray solutions, an effect attributable probably to the
presence of cations in the 'well' water. Reduction in carrier
volume from 600 L/ha to 300 L/ha did not alter the glyphosate
activity significantly.
The influence of several additives on glyphosate
phytotoxicity was studied under glasshouse conditions.
G1yphosate was 1ess phytotox i c when app 1i ed in 100 mM
solution of calcium chloride and zinc sulphate, while the
addition of magnesium sulphate or anmonium bicarbonate, did
not alter glyphosate activity. Of the amonium salts added
to the spray solutions, only ammoniumsulphate and urea at
0.5% enhanced the glyphosate activity.
Non-ionic surfactants "AGRAL-90", and SURFACTANTN" both at 0.1% and 1.0% very significantly increased the
performance of glyphosate, indicating that surfactant use
should become a general recomnendation with glyphosate. A
number of selected petroleum and vegetable oils used as
adjuvants did not make significant alteration of glyphosate
activity. When the pH of the spray solution was altered,
glyphosate at pH 6 exhibited the best phytotoxic activity
against the torpedograss.