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Central Iowa Crop Update
Updates from an agronomist and weed nerd in central Iowa.
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In this issue:
- Harvest and Grain Storage Resources
- A New Weed To Watch: Asian copperleaf
- Not Too Late for Weed Control
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Harvest and Grain Storage Resources
Harvest is in full swing in central Iowa and it sounds like progress is going well and yields are about as expected (or maybe a little higher?!). Safety and accuracy in data collection is always front-of-mind this time of year. Check out the resources and information below.
Corn grain moistures still seem to be quite high, which makes sense due to the later planting and long relative maturities many plant. For those who don't have the capability to dry grain on farm, be sure to monitor fields for stalk integrity in the coming weeks.
Soybean harvest is moving along as well. I have been hearing primarily about two issues: (1) soybeans at harvest moisture with green stems and leaves still on the plants and (2) soybean plants that appear harvest ready but have green pods and beans.
- Soybean plants with tough stems and leaves require sharp sickle bars and patience to move through the field at a slower speed.
- Harvesting when the soybeans themselves are at the right moisture is the right move, whether that requires slowing speeds a bit or waiting a bit longer.
Slowing down harvest is always a concern, but harvesting soybeans that are too dry is a concern as well. Soybean dry down rate is very quick once they reach maturity as shown in this 2017 ICM News article. UNL had a nice summary of potential yield losses just from moisture loss in soybean several years ago and it was reprinted on the No-Till Farmer website in 2016 with some more information (see table below); note these numbers are strictly from moisture loss in the beans harvested, not accounting for increased shatter losses.
| Moisture Level |
Potential Yield Reduction |
| 12% |
1.14% |
| 11% |
2.25% |
| 10% |
3.30% |
| 9% |
4.40% |
| 8% |
5.43% |
Soybeans that caught (or will catch this weekend) frost, like replant areas, may have more shatter issues and green soybeans that affect grading. Additionally, moisture meters may read low on these after a frost event. Read more about frost on soybeans here.
Some sources have reported discolored hilums on soybean seed, in some cases enough to result in dockage for a higher than allowable % soybeans of other colors (SBOC) to qualify them for #1 grading. This appears to be associated with some Enlist soybeans, though it is likely to have an environmental component in addition to a genetic one. If you notice discolored soybean hilums during harvest, especially if you get docked for them at market, please let me know! Read more about this issue here.
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A New Weed To Watch: Asian copperleaf
Acalypha australis (Asian copperleaf) images taken on Sept. 29 in Grundy County. Images courtesy of Robin Pruisner and Bob Hartzler.
Please keep an eye out for a new weed spotted in eastern Iowa in the past several years. We know very little about Asian copperleaf (Acalypha australis) but we need to learn where it is in order to begin understanding how it is behaving in our environment. This species is native to parts of Asia and Australia and is known to have biotypes resistant to HG 9 (glyphosate) and HG 14 (fomesafen) herbicides in its native range. More detail is available in this ICM News article but a summary is below too!
- History in Iowa: It was first spotted in a corn field in 2016 in Black Hawk County and found in a soybean field in Grundy County this fall. Both infestations had fairly consistent stands of the weed.
- Identification: annual species reproducing by seed; most plants reach only 18" tall, erect plant with alternate lanceolate to ovate-shaped leaves that have serrate (toothed) leaf margins; several Acalypha species are found in Iowa, but this species has circular to heart-shaped bracts surrounding the flowers
- All other Acalypha species found in Iowa have deeply lobed bracts (see image comparison)
- Requested Action: The Iowa Department of Agriculture and Land Stewardship and Iowa State University are requesting help in determining how widespread this weed is. Please keep an eye out for this species through harvest. If you suspect you've found an infestation, please contact IDALS at 515-725-1470.
Acalypha australis (right image) has circular to heart-shaped bracts while other Acalypha species in Iowa have deeply lobed bracts surrounding flowers. Images courtesy of Bob Hartzler.
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Not Too Late for Weed Control!
The weather is very favorable for treating weeds still this fall. Check out the resources below for more information on treating winter annuals and perennials like dandelion yet this fall in crop fields and on treating biennials and perennials in pasture, hay, and non-crop areas. Now is a fantastic time to treat weeds like musk thistle and Canada thistle. I even wrote an ICM News article last summer on spring treatment of Canada thistle, but the product recommendations remain the same.
Other points to keep in mind
- Aim to treat when daytime temperatures are at least in the 50s, avoid treating immediately after frost, and take advantage of the sunniest part of the day to spray when possible.
- This next week would be an excellent time to treat for biennials and perennials.
- Herbicides can still be very effective after a (or even several) frost event(s). Continue to keep in mind the principles of treating like warm temperatures and making sure plant foliage is in good condition to absorb herbicide. See this article for more information!
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