Spreading weed seed

Tips to Stop Spreading Weed Seed During Harvest

Weeds can spread in a variety of ways, including on farm equipment. As you move harvest equipment from field to field, be aware of the potential to spread weed seed – especially if uncontrolled weeds are known or suspected to be herbicide resistant.

Some steps that can be taken to prevent the spreading weeds when moving harvest equipment from one field to another are listed below.

  • Clean new-to-you equipment so someone else’s weeds are not introduced to your farm.
  • If possible, harvest fields with excellent weed control first.
  • Harvest fields where weeds are or might be herbicide resistant last.
  • Harvest around areas with extremely dense weed populations.
  • Slow the combine to ‘self clean’ between fields:
    • run the unloading auger empty for a minute or two
    • open grain elevator doors, rock tramp, and unloading auger sump then run the separator with maximum air flow and suction

    It is very difficult to completely remove weed seeds from harvest equipment. However, taking a few minutes to reduce the number of seeds on your harvest equipment may save time and money in the future.

    Harvest Weed Seed Control

    At harvest time, weeds that have escaped season long management often have mature seed still attached to the parent plants. These weed seeds can enter the combine along with the cash crop, exit the back of the combine as chaff (small plant pieces and weed seeds), and be spread across the field, as well as from one field to another. It seems a waste to spend all year spraying weeds with expensive herbicides only to reward the survivors at harvest by spreading their weed seeds out for next year.

    An excellent way to stop weeds in their tracks is to collect these weed seeds at harvest and either destroy them or deposit them in a known location where they can be monitored and controlled later. Soybean, wheat, and other crops harvested with a grain header are ideal choices for harvest weed seed control (HWSC). Other crops such as cotton and corn need further equipment development to make HWSC a viable option.

    If you are considering adding harvest weed seed control (HWSC) to your weed control program there are excellent resources on the WeedSmart website to help guide you through the initial decisions and the implementation of this important weed control tool.

    3 steps to get it working for you

    1. Decide which system fits your farm best.

    2. Get maximum weed seed into the header.

    3. Know how to manage the collected weed seed.

    What is Harvest Weed Seed Control?

    Choose The Best System For You

    Which system is best?

    HWSC is being rapidly adopted in Australia and other countries around the world. There are six systems currently being used on Australian farms and they have been initially developed by farmers.

    Research has demonstrated that all are very effective weed seedbank management tactics for a range of weed species, achieving over 80 percent control and for some nearly 100 percent.

    See HWSC in Action

    Over 80% weed control for species that retain seed at harvest

    Crop residue management

    There are six systems currently used to collect and manage weed seed at harvest. They can be grouped according to the way crop residue is managed: chaff only or chaff + straw.


    Chaff carts are a tow-behind unit on the combine that collects the weed seed-laden chaff, which can then be placed into piles that are later either grazed by livestock, burnt, or both and sown through the following season. Chaff carts are often chosen for use on mixed cropping and livestock farms in Australia as the chaff is an excellent livestock feed; however, spreading manure back onto fields can allow for further seed spread.

    Chaff lining funnels the chaff and weed seeds into narrow rows behind the combine, where the residue is left to overwinter. The weed seeds are exposed to natural elements that can lead to weed seed decay and predation. Typically a follow-up herbicide application is required. – Chaff lining is usually considered a good entry-level HWSC option.

    Chaff decks (chaff tramlining) are similar to chaff lining, but place the chaff in one or both of the combine’s wheel tracks. The added compaction from the wheels can be beneficial in controlled traffic systems.

    Impact mills run the chaff through a mill that pulverizes (destroys) the weed seed, which is then spread across the fields. This technology is usually considered the ultimate in HWSC.


    Bale direct collects all the crop residue directly from the combine and compacts it into large bales suitable for sale.

    Narrow windrow burning collects all of the crop chaff and straw residue, and funnels it into narrow rows in the field. These rows are burnt to destroy the weed seed. This method is effective but removes all of the crop residue from the field.

    Learn More About Each System in This Research Report

    Calculate the cost

    While each HWSC tactic is similarly effective in collecting weed seeds , they vary considerably in capital and ownership cost, nutrient removal costs, operational costs, and labor costs. Some HWSC tactics involve the purchase of substantial machinery – such as an impact mill, chaff cart, or chaff deck – but the operational and labor costs might be lower than methods such as narrow windrow burning, which involves low set-up costs but higher nutrient losses and labor costs associated with burning. Chaff lining is often chosen as the best entry-level tactic that requires minimal set-up cost, no additional labor and minimal nutrient loss or redistribution. To calculate the cost of each method for your farm you can use a calculator developed by WeedSmart’s Peter Newman. Download the calculator or learn more @ Calculating the cost of HWSC for your farm.

    Spreading weed seed

    Weeds reproduce and spread by many methods and may have special adaptions to assist their dispersal. These include seeds, spores, runners and separated root and shoot fragments. Nature plays a big part in spreading weeds over small distances in wind and water. Humans, unfortunately, are by far the worst offenders at spreading weeds, particularly on dirty tools, machinery, vehicles, clothing and transported animals. Some of the more common methods of weed spread and methods used to prevent this are discussed as follows:

    Stock Feed – Contamination of hay and grains with wet seeds is one of the most common means by which weeds are spread. Feeding animals in a confined area or in one paddock reduces the risk of weeds invading the rest of the property.

    Stock – Weed seeds ingested by stock can remain viable after passing through the digestive tract. New stock should therefore be confined to one paddock for a week after arrival. This allows time for any viable seeds that have been ingested by the stock to be expelled. Seeds which are sticky or spiny can spread on the animals, for example in sheep fleece.

    Machinery – After using machinery in weed-infested areas ensure they are thoroughly cleaned. Weed seed can be transported in tyres and in other road materials.

    Soil Disturbance – Minimise the amount of soil and vegetation disturbance when carrying out work. Disturbed ground creates an ideal seed bed for both existing and introduced weed seeds to germinate.

    Humans And Animals – Check your own clothing, socks, cuffs, jumpers, boots etc. after walking through weed-infested areas. Remove and destroy and seeds you find. Dogs and cats can also disturb seeds in their coats, as can wild animals, particularly vermin such as foxes and rabbits. Birds also transport seeds when they feed on wet fruits and seeds such as blackberry and cotoneaster.

    Garden Escapees – Many weeds were introduced to Australia as ornamental plants or for herbal medicine, which have since “escaped” from our gardens and become wild. For example – pampas grass, broom, Spanish heath and cotoneaster. It is best to avoid “weedy” species when choosing plants for your garden.

    Water And Wind – Wet seeds entering waterways or drains can be spread to new areas downstream. On windy days when plants are seeding, the wind can easily disperse the seed quite some distance. Many weed species have seeds especially adapted to be carried by the wind.

    Explosive Projection – Many weeds such as gorse disperse their seeds through explosive projection. The seeds are encased in pods, which can be thrown up to several metres from the parent bush.

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