Eric Yu, Extension Educator – IPM Crops, Dave Nicolai, Extension Educator – Crops
As harvest approaches, now is a good time to scout fields and field edges for weeds that escaped earlier control. Mowing fence lines, field edges and other non-crop areas can help prevent weeds from producing seed and reduce the potential for weed seeds to move into fields during harvest.
Despite the drier conditions across much of Minnesota this year, weeds continue to emerge and develop in fields and along field edges. Take time now to identify and manage these weeds before they produce additional seed and replenish the soil seedbank.
Waterhemp is especially important to manage because it can produce viable seed within 10 days of pollination and is capable of producing hundreds of thousands of seeds per plant (Bell & Tranel, 2010). Preventing weed seed production from even a few plants can reduce future weed pressure, for example lambsquarters has been reported to produce up to 30,000 seeds per plant.
When scouting, also check field entrances, roadsides, waterways, shelterbelts, low areas and other locations where weeds may have escaped control.
Mowing is less effective once mature seed is present, but it can still prevent additional seed production. Do not assume that all seeds present on a plant are mature and viable, because the timing of seed development varies by species. To avoid spread of weeds from the field edges, keep grassy margins and driveways mowed frequently enough to prevent seed production. Regular mowing will also force perennials to put energy into shoots rather than into roots or rhizomes that spread into the field.
If practical, clean harvest equipment after working in heavily infested fields or patches before moving to clean fields.
Be particularly alert for unfamiliar or potentially noxious weeds such as Palmer amaranth. Early detection and removal of a few plants is much easier than managing an established infestation. For more information, see Preventing Palmer amaranth in Minnesota.
Walk field edges and problem areas now, mow weeds before mature seed develops, and mark significant weed patches before harvest. Pay particular attention to weeds concentrated along field margins. If a weed is more abundant near the edge of a field and less common farther into the field, the field margin may be an important source of new weed seed. In these areas, additional management of fence lines, field borders, or other adjacent areas may help reduce future weed problems.
Even under this year's dry conditions, weeds have the potential to produce large quantities of seed. Preventing seed production and limiting seed movement now can reduce weed pressure and make management easier in future seasons.
Hill EC, Renner KA, VanGessel MJ, Bellinder RR, Scott BA. 2016. Late-season weed management to stop viable weed seed production. Weed Science 64:112–118.
Bell MS, Tranel PJ. 2010. Time requirement from pollination to seed maturity in waterhemp. Weed Science 58:167–173.
Ditommaso A, Mohler CL, Teasdale JR. 2021. Manage Weeds on Your Farm-A Guide to Ecological Strategies. SARE Handbook Series16.
Despite the drier conditions across much of Minnesota this year, weeds continue to emerge and develop in fields and along field edges. Take time now to identify and manage these weeds before they produce additional seed and replenish the soil seedbank.
Scout for escaped weeds
Many weeds in corn and soybean fields are flowering or developing seed. Pay particular attention to waterhemp and other pigweed species, giant and common ragweed, kochia, common lambsquarters and annual grasses.Waterhemp is especially important to manage because it can produce viable seed within 10 days of pollination and is capable of producing hundreds of thousands of seeds per plant (Bell & Tranel, 2010). Preventing weed seed production from even a few plants can reduce future weed pressure, for example lambsquarters has been reported to produce up to 30,000 seeds per plant.
When scouting, also check field entrances, roadsides, waterways, shelterbelts, low areas and other locations where weeds may have escaped control.
Mow before seeds mature
If weeds along field edges have not yet produced mature seed, mowing can substantially reduce viable seed production. Research conducted in Michigan and Delaware found that terminating several common weeds before seed maturity reduced viable seed production by 64 to 100%, although results varied among species and timing (Hill et al., 2016).Mowing is less effective once mature seed is present, but it can still prevent additional seed production. Do not assume that all seeds present on a plant are mature and viable, because the timing of seed development varies by species. To avoid spread of weeds from the field edges, keep grassy margins and driveways mowed frequently enough to prevent seed production. Regular mowing will also force perennials to put energy into shoots rather than into roots or rhizomes that spread into the field.
Minimize weed seed movement during harvest
Combines are an effective way to move weed seeds within and between fields. Before harvest, identify significant weed patches and consider harvesting relatively clean areas first and weedy areas last. This can reduce the opportunity for seeds to be spread throughout otherwise clean portions of the field.If practical, clean harvest equipment after working in heavily infested fields or patches before moving to clean fields.
Be particularly alert for unfamiliar or potentially noxious weeds such as Palmer amaranth. Early detection and removal of a few plants is much easier than managing an established infestation. For more information, see Preventing Palmer amaranth in Minnesota.
Take action before harvest
The window for preventing weed seed production is closing quickly. For example, under short day late summer conditions, pigweed species flowering can occur in three weeks with seeds maturing three weeks later. Redroot pigweeds continue to flower and produce mature seeds until frost. To detect mature seeds, rub a portion of the flower cluster between your fingers and look for hard black seeds.Walk field edges and problem areas now, mow weeds before mature seed develops, and mark significant weed patches before harvest. Pay particular attention to weeds concentrated along field margins. If a weed is more abundant near the edge of a field and less common farther into the field, the field margin may be an important source of new weed seed. In these areas, additional management of fence lines, field borders, or other adjacent areas may help reduce future weed problems.
Even under this year's dry conditions, weeds have the potential to produce large quantities of seed. Preventing seed production and limiting seed movement now can reduce weed pressure and make management easier in future seasons.
References
Hill EC, Renner KA, VanGessel MJ, Bellinder RR, Scott BA. 2016. Late-season weed management to stop viable weed seed production. Weed Science 64:112–118. Bell MS, Tranel PJ. 2010. Time requirement from pollination to seed maturity in waterhemp. Weed Science 58:167–173.
Ditommaso A, Mohler CL, Teasdale JR. 2021. Manage Weeds on Your Farm-A Guide to Ecological Strategies. SARE Handbook Series16.
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