Torpedograss (Panicum repens L.) control with lower rates of glyphosate

Abstract

The effect of glyphosate [N‐(phosphonomethyl) glycine] applied as foliar sprays, on the shoot growth, regrowth from ‘crown’ and rhizome bud‐viability of perennial torpedograss (Panicum repens L.) was studied. In general, rates of 1.0–4.0 kg a.i./ha killed 80–100% of aerial shoots and suppressed 90–100% of regrowth from treated plants. Rates above 1.0 kg a.i./ha also killed 80–97% of rhizome buds within 7 days of spraying. Rates below 1.0 kg/ha gave insufficient regrowth suppression and bud‐ kill and were not adequate to control well‐established, mature plants. Plant age was a factor which affected glyphosate control of the weed, and while the young plants under 8 weeks of age were effectively killed by lower rates, the killing of older plants up to 20 weeks of age required rates above 1.0 kg/ha. Although rhizome length was not a major factor influencing the killing of rhizome buds by a range of rates of 0.5–4.0 kg/ha, the results of several experiments indicated that a rate close to 4.0 kg/ha was needed for a 100% kill of all rhizome buds in well‐developed rhizome systems. At 2.0 kg/ ha, the herbicide required a minimum of 6 h duration on torpedograss foliage to reduce regrowth significantly. With a lower rate of 1.0 kg/ha, significant regrowth reduction took place only after the herbicide had been on the foliage for 72 h. Superior control of torpedograss was obtained by split, sequential applications of glyphosate within the range of 0.5–2.0 kg/ha, compared to one full‐rate application. A split application of a total dose of 1.5 or 2.0 kg/ha completely prevented regrowth, and achieved 85 to 95% bud‐kill.

Keywords:

• torpedograss
• Panicum repens
• Chemical control
• low‐rates
• split‐applications
• glyphosate