Weed competition takes on tropicals
From the April 2008 edition of Agriculture Today.
Annual summer grass weeds are one of the biggest threats to successful establishment of tropical perennial grasses, particularly in Northern NSW where liverseed, barnyard and stink grass are tough competitors.
When tropical grass pastures cost in excess of $300 per hectare to establish, annual grass weed control becomes a high priority.
Many successful growers allow two years of annual summer grass control prior to planting the pasture, which is now backed up by a recent experiment as part of the Co-operative Research Centre for Future Farm Industries.
The fallow weed control experiment was conducted by researchers at NSW Department of Primary Industries’ Tamworth Agricultural Institute on the Manilla property "Leaholme", owned by the Faulks family.
Comparisons were made between three treatments - two summers of weed control, one summer of weed control and weed control in the spring prior to sowing on November 26, 2007.
A bandseeder with press wheels was used to sow Bambatsi panic into a prepared seed bed as it was easier to distinguish from the annual grasses liverseed and barnyard.
Fourteen days after sowing there was on average of 320 Bambatsi plants per square metre (see table).
With less than two summers of annual grass control, the population of liverseed and barnyard grass severely affected the establishment and early forage production of Bambatsi panic.
Dry matter production of Bambatsi was reduced by 59 per cent with one summer of control and by 91pc with only the spring prior to sowing used to control annual grasses.
"The experiment is yet to have a second assessment but I do not expect any improvement in the weedy plots," NSW DPI researcher, Dr Greg Lodge said.
"This summer was ideal for the establishment of tropical grasses but in tighter seasons the risk of failure will increase."
As there are no selective herbicides for annual grasses in establishing tropical grass pastures, summer grass control over two summers before sowing is essential to reduce the competition impact.
The weed seeds of liverseed and barnyard grass are easily distinguished in a handful of soil so a quick check could save you money.
Contact Lester McCormick, technical specialist pastures (North), Manilla, 0427 401 542.
