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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.

    How Herbicide Resistant Weeds Spread

    Spread via field machinery is a primary way that herbicide resistant seeds spread from field to field and across state lines. While driving through an infested field, it is very easy for weed seeds to get stuck in small nooks within combines, mowers, and tillage equipment. Combines are a particular source of seed spread, because:

    1) They go through fields during the time of year when escaped weeds are producing seed

    2) They harvest whole plants including the weeds, and

    3) They have many small spaces where seeds can hide.

    If herbicide resistant weeds have survived management attempts and remain at harvest, it is important to thoroughly clean the combine after harvest and to harvest infested fields last. Do not use combines that have recently been in infested fields. In severe cases, producers have chosen to forgo harvesting fields with heavy infestations of Palmer Amaranth or waterhemp in order to avoid spreading the seeds to other fields. For more information on preventing weed dispersal via equipment, please visit our tips for preventing the introduction of resistant weeds.

    Seed, Grain, and Seed Mixes

    When bin-run cash crop seed is purchased from agricultural areas where herbicide resistant weeds are present, weed seeds mixed in with the cash crop seed can be transported to other fields at planting. Best management practices advise only planting certified crop seed. Certification programs are state-specific but always require diligence to ensure that harvested crops do not contain problem weed seeds. Some states have noxious weed laws in place to discourage the distribution of contaminated seed. If contaminated seed mixes are planted, it is quite likely that the weed seeds will germinate and start an infestation in that field. It is highly recommended to aggressively scout and control weeds after planting to ensure that any weeds in the seed mix are not allowed to reproduce and further spread.

    Case study: As of September 9, 2016, Iowa State University weed scientists have confirmed the recent introduction of Palmer amaranth to 28 Iowa counties. In 20 of these counties, introduction occurred via the establishment of native seed mixes for conservation plantings. In the remaining eight counties, the weed introduction was traced back to conventional farm operations. According to Meaghan Anderson, ISU Field Agronomist, hand-pulling individual plants as early as possible is the preferred method to eliminate the weed in conservation plantings. She goes on to say:

    “The establishment of Palmer amaranth in conservation planting across the state is unfortunate. However, the long-term impact of the contaminated seed mixes can be minimized by responding accordingly. Seed mixes purchased from several seed producers/vendors have been the source of Palmer amaranth. Fields planted with native seed mixes earlier this spring should be scouted as soon as possible to determine if Palmer amaranth is present. If found, there is still time to minimize seed production and the risk of Palmer amaranth spreading into crop fields in the area. Since some viable Palmer amaranth seed is likely present, take appropriate precautions to prevent moving seed from source fields with mowers or other equipment.”

    Palmer amaranth in Iowa counties was found as early as October 31, 2016; date of infestation varied depending on setting (conservation or agricultural land, or railroad right of way).

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