IN THE battle to reduce weed numbers, incorporation of oaten hay in a rotation has proved very effective in depleting weed seed banks.
This result has emerged from research, supported by growers and the Federal Government through the GRDC, which was conducted by the Alma and Tarlee Land Management Groups in the lower north of SA.
According to agronomist Tony Craddock of Rural Directions, who worked with the groups for the four years of the project, oats are competitive with weeds; they enable the use of alternative herbicides to control herbicide-resistant ryegrass and, during haymaking, ryegrass seedheads are cut and removed from the paddock.
"The groups have found, however, that for haymaking to be effective, control of regenerating rye grass seedheads is essential," Mr Craddock said. "While not as effective as hay, the groups' research has also shown canola to be very useful in depleting, or at least not increasing, the weed seed bank."
The groups arrived at some answers on other strategies as well.
Crop-topping - this has transformed pulses from being a weak link in the rotation, as far as herbicide-resistant ryegrass management is concerned, to a strong one. Mr Craddock said that peas, for example, proved well suited to managing herbicide-resistant ryegrass. They were optimally sown later in the cropping program, allowing control of early ryegrass germinations, and tended to mature earlier than beans, lupins and lentils, allowing crop-topping to be conducted with less impact on yield.
Competitive cereals - blow-outs in seed-bank levels were often associated with crops of poor competitive ability such as Yallaroi durum and Janz wheat. Mr Craddock said even varieties recognised as having good competitiveness suffered blow-outs when drought, herbicide damage or poor establishment impaired their competitive ability.
High risk - beans or lentils followed by Yallaroi durum were found to be high-risk sequences and, to overcome this, farmers now crop-topped or windrowed their beans and had switched to the more weed-competitive Tamaroi durum variety.
Pastures - first-year pastures proved a weak link in managing the ryegrass seed bank because they were less competitive and farmers were reluctant to heavily graze or spraytop them. However, where pasture phases of two years or more were practised, ryegrass seed-bank levels were significantly reduced in nearly all of the paddocks monitored. (See also lucerne case study, this page.)
According to Mr Craddock, spray-topping in managing ryegrass in pastures was more effective when the pastures were mechanically topped before spray-topping, as more even ryegrass seedhead emergence occurred.
"Behind the scenes, the growers in the project all use high seeding rates, ensure good crop nutrition and aim for timely sowing to maximise competitiveness with weeds," Mr Craddock said.
"There is also a high level of attention to detail - such as control of 'escapes' after hay cutting, strategic grazing to prevent ryegrass seedset, and care in applying herbicides at optimum timings and rates.
"Despite all this, things go wrong and blow-outs in the ryegrass seed bank sometimes occur and so, each autumn, group members review graphs of their weed seed-bank trends. But overall, "there is no doubt the strategies they have adopted are working".
Program 3 Contact: Mr Tony Craddock 08 8842 1103