How to manage grass seeds

There are no easy answers to grass seed control, but the good news for producers is there are grass seed management options available to suit all production systems.

Sheep industry consultant, Geoff Duddy, said sheep producers who successfully managed seeds relied on a combination of short, medium and long-term strategies.

“Although grass seeds only threaten livestock a few months of the year (late spring through summer is the risk period) controlling them needs to be a year-round focus,” Geoff said.

“Grass seed management should be part of good pasture management regardless of the time of year.”

He said it was important to assess the best combination of agronomic, grazing or management strategies for the season, and for individual production goals.

If seed has set and there are no seed-free paddocks, short-term options include:

• Feedlotting – relocate stock out of seedy paddocks to avoid grass seed contamination.
• Early turn-off – only if sheep are seed-free (don’t make seeds someone else’s problem).
• Strategic grazing – this enables priority stock, such as lambs, to graze low-risk paddocks.

Effective strategies to employ a couple of months before seed set include:

• Spray topping – If paddocks with problem annual grasses are identified early in the season, graze heavily over spring and remove stock two to three weeks before grass maturity (for uniform grass seed heads). Apply a non-selective herbicide between head emergence and the milky doughy stage (depending on chemical used) to prevent seed set.
• Spray grazing – Spray broadleaf weeds when they are 6-8 weeks old with a low rate/ sub-lethal dose of a selective herbicide. Plants wilt, increasing sugar levels and palatability. After 7-10 days, graze the paddock at 4-5 times the normal stocking rate. Avoid grazing pasture below 3cm to prevent damage to desirable plants. This technique is most effective in the two weeks after spraying.
• Premature shearing – Shear before seed set to reduce grass seed contamination of wool. This is also a good long-term option for producers who don’t wish to use chemicals (or have resistance issues), or if all paddocks have a seed risk.
• Winter cleaning – To manage pastures badly infested with silver grass, and to a lesser extent barley and brome grass, spray before they set.
• Mechanical control – Harrowing or slashing long pastures reduces the likelihood of grass seeds entering the eyes of sheep, and works well in conjunction with early shearing.

Producers can also implement longer-term options, such as:

• Fodder crops and improved pastures – Replace problem grasses with more productive and nutritious feed. Grazing management and soil fertility are important to maintain a competitive, improved pasture that will keep weed invasion to a minimum. Options include oats or a combination of oats and vetch, barley and vetch, and pulses (peas, beans, vetch).
• Genetics – Selective breeding enables lambs to reach target weights early, so they can be sold before the main grass seed period.

“Even keeping 1-2 paddocks seed free may be sufficient to substantially reduce the impact of grass seeds on your operation,” Geoff said.

He added that producers should be aware that efforts to provide ‘clean’ pastures can be undone by not paying attention to uncontrolled grass seed.

“Seed pick-up risk can be reduced by keeping all laneways, holding areas, tree lines and sheep camps free of grass seeds and avoiding mustering or handling stock during high-risk times.”

Grass seed management calendar

More information:

• Grass seeds resources: Winning against seeds booklet and video tutorials
• Your agronomist can provide information about appropriate herbicides to use in spray topping and winter cleaning

Tip:

A trial lamb kill can test the effectiveness of grass seed management. This involves processing small lines (20–30 head) of representative lambs to predetermine the likelihood of seed infestation. Producers can use this feedback about grass seed incidence to make better on-farm grass seed management decisions. This strategy has been promoted in South Australia for many years, but the distance to processors in other states can make trial kills unviable.