Options for managing grass seeds

The strategies below can be used at different times to manage grass seeds.

Find out more about how these strategies can be implemented on-farm below. 

 Watch video tutorials* on premature shearingwinter cleaningspray grazing and spray topping
Strategy  Timing

Risk is imminent 

This is the high risk period when seed has set - around spring


Two or more months before seed set - around autumn/winter/early spring

Medium to long-term

Three or more months before seed set - summer/autumn 

Selling lambs earlier



Stock movement


Premature shearing 


Harrowing and slashing


Fodder conservation



Strategic grazing



Winter cleaning

Confinement/forage crops


Spray grazing


Spray topping




Pasture improvement

Change flock structure

Change lambing time



Selling lambs earlier

Producing feeder lambs offers a potential solution for properties that cannot avoid seed contamination of finished lambs. Under this system, a smaller lamb is turned off and the late lactation needs of the ewe are better matched to the length of the spring.

Before changing to a feeder lamb system it is important to do some market analysis and production planning to determine if the change will be more profitable. For more information read pages 23-24 of Winning against seeds manual.

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Stock movement

Know when your high risk periods are and avoid mustering or handling during this time. Ensure all lane ways and holding areas are free of grass seeds. This also ties in with the need for a compact lambing period, not only to minimise labour requirements but also to allow early weaning if necessary.

Another way to reduce the amount of grass seed pickup is to provide access to watering points via pathways radiating across paddocks. The pathways can be cleaned chemically or mowed to reduce the amount or height of seed heads. This can help reduce, but not eliminate, grass seed pick-up, as long as sheep are mustered slowly and not disturbed by dogs during the high-risk seed dispersal period. Similarly, moving lambs on cool, damp mornings will reduce pick-up.

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Premature shearing
Shearing before grass seeds become a problem reduces grass seed pick-up and seed penetration of the skin, although it won’t completely eliminate seed pick-up.

Shearing alone should not be relied upon as the sole strategy to minimising the impact of problematic seed species. The degree of seed pick-up is partly related to wool length and type. It is also related to the timing of wool removal before the high-risk seed dispersal period, with the barest sheep during this period having the lowest levels of skin penetration from seeds, and subsequently, having the highest weight gains.

It is important to weigh up the cost-benefit of shearing lambs, especially Merinos, against other approaches that avoid the need for premature shearing. Shearing prime lambs purely for market preference is questionable as premiums or discounts often do not absorb the extra cost of shearing.

Many trials have shown that, when grass seeds are not an issue, shearing does not increase growth rates of young sheep when compared with leaving them woolly. In practice, shearing itself may well depress weight gains in the short term, especially if followed by inclement weather.

Lambs and weaners can be shorn as a short-term response to grass seeds in the lead-up to seed set.

When considering the cost-benefit of premature shearing of lambs, take into account the:

  • potential skin value gained for shorn lambs when they are sold
  • cost of shearing
  • wool income
  • risks associated with not shearing such as seed contamination, flystrike and belly dags in a feedlot situation

Harrowing and slashing

Grass seeds can be knocked to the ground by dragging harrows or implements such as old tyres across a grassy pasture late on a hot day. While this reduces the seed contamination risk, there is still potential for some seed pick-up because the grass seeds have not been removed from the system. To reduce seed pick-up, use shorn sheep to graze these paddocks.

This practice is best used as an interim approach while long-term strategies are put in place or where adequately clean areas can not be achieved through other means.

Sale-stock grazing harrowed pastures need to be monitored carefully for seed pick-up and removed from the paddock immediately if seed contamination becomes evident.

Machinery and equipment used for harrowing needs to be inspected for weed seeds thoroughly and cleaned before removing it from infested paddocks. This is especially necessary for paddocks containing Chilean needle grass (Nassella neesiana) as it is readily spread by attachment to machinery.

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Fodder conservation

Fodder conservation can assist in seed control by removing grass seed heads from a paddock and creating a grass seed-free environment for grazing stock. When conserving fodder such as hay or silage, plan early, apply adequate fertiliser, use timely insect and unwanted weed control.

After harvest, follow-up with glyphosate or heavy grazing to stop regrowth from developing seed heads.

Conserving fodder provides a source of quality feed that can be used to finish lambs in a seed-free environment such as a feedlot.

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The risk of grass seed infestation of sheep and lamb carcases, skin and wool is often a transitory event, for which short-term containment in a feedlot or small paddock can be a viable management option.

The most important aspect in regards to using feedlots as a management tool is to ensure lambs are free of grass seeds prior to entering the feedlot. Grass seed management must be addressed before this stage, including seeking assurances of seed status when purchasing lambs.

While an elaborate establishment is not required, the area needs to be clean, adequately sloped and well drained. Shade and shelter are also required to minimise the risk of cold or heat stress. Adequate separation distance should be maintained between the feedlot and any sensitive receptors such as houses, waterways or public areas.

It is important to determine the nutritional requirements of different classes of sheep during the containment period.

Dry ewes, rams and wethers will maintain condition on lower quality feeds while weaner lambs and replacement ewe lambs have higher nutritional requirements for maintenance and growth. Ideally, seek professional advice about the most cost-effective ration to feed until paddock feed once again becomes an option.

Read the report, National guidelines for the design and management of lamb feedlots and containment areas, for detailed information.

Key management factors include:

  • slowly introducing lambs to grain before placing them in the feedlot to prevent grain poisoning (acidosis)
  • a suitable vaccination program before entering the feedlot
  • providing calcium and salt in the form of a loose lick if the diet is cereal based
  • providing a constant supply of fresh water and cleaning troughs regularly to maximise water intake
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Strategic grazing

Use grazing management to manipulate pasture composition and reduce the total number or height of seed heads to minimise their impact on young sheep. Manipulating pasture composition and ground cover in conjunction with improving soil fertility effectively controls and reduces the impact of grasses such as wire grass, spear grass and silver grass.

Heavy grazing, burning or slashing, undertaken either individually or in combination during emergence of seed heads, will reduce seed set. With appropriate rest periods, other more desirable species can then out-compete problem species and improve pasture productivity.

Grazing management to control seeds from annual grasses is most effective where pastures maintain a strong perennial base. Perennials have the greatest capacity to respond after grazing and supply feed to maintain weaners, even after heavy spring grazing has removed problem seed heads.

To achieve this, lock up paddocks for 30 days after heavy late winter and early spring grazing to synchronise seed head development in annual grasses.

After the annual grasses have reached the  jointing stage - when nearly all tillers have noded but before they have produced seed heads - graze the paddocks down to 800-1,000kg dry matter/ha with at least 200 DSE/ha over four to five days. This is preferably carried out with cattle, worm-free wethers or dry ewes. Re-stock the paddock with weaner lambs or lactating ewes when pastures reach target levels of 1,500kg of high-quality green dry matter/ha.

During spring, with pasture growth rates of 40-80kg dry matter/ha/day, it will only take two weeks to reach this target, after which it could be stocked with either 20-40 weaners/ha or 11-22 lactating ewes/ha. Rotational grazing is recommended on lucerne pastures.

Heavy grazing during late winter and early spring will also potentially lengthen the vegetative stage of the grasses and improve their summer nutritive value. The effect on annual grasses is the reduction in the height and size of the seed heads, which leads to a reduction in seed pick-up and their impact on the eyes of young sheep.

This grazing management strategy can be effectively used in extensively grazed lower rainfall areas, where chemical control may be limited to sheep camps and the only pasture improvement option may be lucerne at 20–30 plants/m2. However, such grazing management, which tends to increase tillering, is also likely to increase the number of barley grass seed heads and attention to seed management must be strict.

Making silage, which is similar to heavy grazing during the stem elongation phase, can be used to prepare high-quality grass seed-free pastures for weaner sheep. It will be less effective in long-flowering grasses (such as silver grass).

In northern New South Wales and southern Queensland, expanding the area of improved perennial pastures or manipulating wiregrass dominant pastures to more favourable Wallaby grass (Austrodanthonia spp.) and Weeping grass (Microlaena spp.) dominant pastures will significantly reduce the impact of problem grasses on farm profit and production. This is achieved by strategically burning the pastures in late winter or early spring, before heavily grazing pastures during summer and autumn. This leads to increased vegetative growth of the wiregrass during the summer-autumn  period, and with concurrent rotational grazing during the winter it will encourage the dominance of Wallaby grass and Weeping grass.

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Winter cleaning

In lucerne and annual pastures the winter cleaning approach, conducted when soil moisture conditions are good, can result in virtually grass-free paddocks, and the control of many broadleaf weeds.

In addition to providing grass seed-free areas for lambs, winter cleaning also has the added benefit of increased pasture growth. The removal of grasses from the pasture results in the pasture becoming legume dominant. This can lead to potential stock losses due to redgut if fibre is not provided in the diet. Contact a veterinarian for local recommendations.

Annual pastures: Winter cleaning of annual pastures can be done relatively early in the season. For removal of grasses (except silver grass) from a medic pasture, various grass herbicides can be used. Broadleaf weeds can also be targeted relatively early, conserving moisture and nutrition for more desired pasture plants. Contact your local agronomist to determine specific herbicide and management options.

Lucerne: Mature lucerne stands can be cleaned of grass and broadleaf weeds using high rates of products like Sprayseed®, Simazine® and Diuron®. Raptor® can be used when it is not desirable to temporarily burn Lucerne stands for weed control. This chemical is very soft on lucerne and when applied early, controls silver grass and a number of other grasses effectively. It does this whilst not taking out veldt grass - so the end result is a lucerne/veldt pasture.

Confinement/fodder crops

Fodder crops enable lambs to be removed from pasture with potential grass seed problems into clean paddocks. Fodder crops are usually sown between winter and early spring. Staggered sowings enable lambs to be fed on one area for a set period and then moved into a fresh paddock.

A late-season option in dryland areas may be grazing mature grain crops rather than green herbage but be wary of associated health risks.

Along with animal production benefits, fodder crops improve the nitrogen and organic matter content of the soil and certain crops can assist in root disease control. There are many fodder crop options, enabling a choice that is best suited to the environment and production system.

Fodder crops include:

Oats, or a combination of oats and vetch: Using herbicides to manage grass weeds in this mix can be difficult, other than hay freezing at the optimum time. If involved in cropping, this fodder crop is best sown into a clean paddock from the previous season where Simazine® and Verdict® have been used to reduce silver grass and geranium (Erodium spp.).

Barley and vetch: Chemical control of grass weeds is easier with this mix but take care with barley during grain fill. Hay freezing is also an option for weed control. 

Pulses: Pulses, such as peas, beans and vetch ,allow easy control of grass weeds but some broadleaf weeds can be an issue, making it best to sow pulse crops later in the season. 

While this can reduce herbage quality, if the crop is allowed to mature before grazing, animals will benefit from the high protein content of the seed.Ensure the associated health risks are managed with fodder crops containing grain and that grass seed set is controlled in all non-arable areas, such as fence lines and gullies. Fodder crops allow higher stocking rates of at least 10-20 lambs/ha (15-40 DSE/ha), depending on whether maintenance or growth is required. Stock health issues when grazing fodder crops must be considered and management options such as deferred grazing, supplementation and increased dietary roughage should be considered. It is best to seek advice to avoid some of the potential pitfalls in growing and feeding them.

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Spray grazing

Spray grazing reduces broadleaf weeds, including Erodium, enabling more productive pasture species to dominate. It can be done in conjunction with a red legged earth mite and lucerne flea control program. Pastures can become grass dominant so careful attention to seed management of the riskier grasses is important.

Spray grazing uses sub-lethal rates of selective herbicide to increase the palatability of broadleaf weeds. After a one-week withholding period, sheep are placed in the sprayed paddock at high stocking rates to graze out the broadleaf weeds over the following two weeks. The higher the stocking rate, the lower the rate of herbicide required. After two weeks, the palatability of broadleaf weeds declines.

While spray grazing can be relatively inexpensive, the use of sub-lethal herbicides requires an effective strategy to be successful. For example, if growing conditions are not suitable for chemical uptake, the impact of spray grazing can be less effective. Developing an understanding of medic and/or subterranean clover and weed growth stages will aid the success of spray grazing. Subterranean clover is more tolerant to hormone-based herbicides than medics.

Having a good plant nutrition program in place can enhance the effects of spray grazing, as the desired pasture species are able to grow away from the chemically suppressed and heavily grazed weeds and out-compete undesirable grass weeds.

Spray topping

Spray topping involves spraying pastures during spring with low levels of knockdown herbicide to prevent viable seed set. Ideal conditions and timing are critical to the success of this technique. Although cheap, success is often low and too much seed ‘escapes’, therefore this approach is increasingly not the answer for managing grass seeds.

Spray topping works best when pastures have an even seed head emergence, but this is often not easily achieved over large areas or with low stock numbers. Heavy grazing before spray topping will encourage synchronised flowering of weeds after which low rates of either Glyphosate® or Paraquat® can be used to thwart seed set.

In paddocks where seed head emergence is not uniform, higher herbicide rates will be required which will effectively hay-freeze the pasture.

Spray topping is most effective on weeds with a short flowering period as this increases the likelihood of the weeds flowering at the same time. Where a mixed sward is present, it is best to target the most damaging weed species and time the chemical application to coincide  with seed head emergence. Attempting to control multiple weed species with a single application will compromise the control of all species.


Moving lambs from grass seed areas, before seed set, to an irrigated pasture system is another option to minimise the risk of grass seed contamination. However, to ensure this is a profitable alternative, do a budget before establishing an irrigation system. Requirements for irrigation depend on pasture type, climate and soils and it will be important to determine the optimal irrigation schedule for each region and production system.

Irrigating perennial pastures extends the time green feed is on offer. Carry out a soil test to determine nutrient requirements and apply phosphorous and nitrogen to increase pasture production. Perennial pastures respond best to rotational grazing.

Only irrigate pastures with good plant composition. Irrigating poor pastures is highly inefficient.

Apply adequate stocking rates to maximise pasture production and maintain perennial pastures in their productive vegetative phase through late spring to early summer. It is important to know the pasture growth curve. A well balanced pasture with little weed infestation can be stocked at 16-25 DSE/ha throughout late spring and early summer, and will provide enough feed to finish 2-3 lots of feeder lambs to trade specifications.

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High performance genetics are an essential input for every sheep business. The increasing use of Australian Sheep Breeding Values (ASBVs) by seedstock breeders enables commercial breeders to predict the genetic performance of sires more precisely.

Using ASBVs, terminal sire ram breeders are averaging 5% genetic gain each year. Maternal and Merino ram breeders are also improving their rates of genetic gain. By increasing animal growth rates genetically, livestock can be turned off at a younger age and before grass seeds become a problem. Alternatively, if seed set allows, animals can be grown on to heavier weights at the traditional turn-off time.

Lambs with high growth rate potential also make better feeder lambs and will be of benefit in areas where grass seeds force producers to move lambs into an intensive finishing system or to sell lambs on to a specialised lamb finisher.

Where alternate finishing systems such as lucerne, fodder crops or lotfeeding are available, high growth rate lambs minimise the time required on the more expensive feed base. Lambs that grow faster also tend to have better feed conversion rates. While growth rate is the key trait influencing profit when selecting prime lamb sires, it needs to be balanced in relation to fat and muscle. Similarly, a sire’s overall genetic package needs to be assessed in relation to the ewe flock.

When considering prime lamb dam selection, consider weaning weight and maternal weaning weight (milk) ASBVs. Ewes with superior ASBVs for these traits will wean lambs heavier at the same age enabling earlier finishing before seeds become a problem.

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Pasture improvement

Pasture improvement uses management practices to promote healthy soils and plants. It is important that pastures receive the best possible start and are maintained to ensure they can out-compete undesirable species in the stand.

When done properly, pasture improvement assists in grass seed management, and delivers the added benefits of being able to carry more stock that are healthier, grow faster and are more fertile. In addition, pasture improvement offers fodder conservation opportunities and the ability to set up paddocks to regenerate year after year.

Before embarking on pasture improvement, ensure the correct grazing management can be applied to maintain persistence and competitiveness of the sown pasture plants.

Critical steps in sowing a new pasture include:

  • determining why the old pasture has run down (grazing strategy, nutrition, seasonal) and ensuring these problems are rectified
  • preparing the new pasture the year before by reducing seed set of unwanted species
  • undertaking soil tests to determine nutritional needs
  • allowing run-down pasture and weeds to germinate and spraying with knockdown herbicide and insecticide
  • inoculating legume seed and sowing into a moist seedbed with adequate fertiliser
  • monitoring emergence of insects and slugs
  • considering broadleaf weed control
  • grazing to promote tillering, seed set in the first season and long-term persistence
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Change flock structure

Changing flock structure in a wool enterprise to increase the proportion of wethers can minimise the amount of grass seed-free country required for lambing ewes or weaners. Increasing the proportion of wethers in a flock will increase total wool production and minimise the number of sheep in the most susceptible classes. However, the ideal structure to maximise profit per hectare will depend on bloodline productivity and the comparative ratio of wool to meat prices.

In a prime lamb enterprise, flock structure can only be adjusted marginally by increasing ewe  reproduction rates. Higher reproduction rates will mean fewer ewes need to be run to produce the same number of lambs.

If this is carried out at the same time as increasing the lambs’ genetic potential for growth rate and improving ewe maternal traits, the same amount of lamb (kg) can be produced per hectare with fewer ewes. These improvements can allow lambs to be weaned earlier and run on prepared seed-safe high-quality pastures.

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Change lambing time

A compact lambing of five to six weeks also reduces the potential scope of the grass seed problem. It enables all operations to be completed (and stock movements minimised) before the high-risk seed dispersal period. For example, completing lamb marking and allowing time for wounds to heal prior to the high-risk period, provides the flexibility to early wean lambs onto seedsafe pastures if necessary.

Lambs weighing as little as 12-15kg can be weaned onto high-quality improved seed-safe pastures but once weaned need to gain weight as quickly as possible until they reach at least 45% of their mature weight. Large pasture areas are not necessary. Considering that spring pasture growth rates can be more than 40-60kg dry matter/ha/day, these paddocks can stock 30-40 weaners/ha without impacting on growth rates or pasture quality and quantity.

Bringing lambing forward to avoid problems is an expensive way to address grass seed problems.

An autumn or early winter lambing always incurs a stocking rate penalty, higher supplementary feeding costs, lower fertility rates in ewes and lower lamb growth rates. Lambing at this time also tends to generate the lowest levels of profitability in prime lamb and wool producing flocks, especially if operating on perennial pastures.

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*The grass seeds video tutorials were produced by Meat & Livestock Australia and supported by the South Australian Sheep Advisory Group.

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