Uncontrolled weeds in soybeans can cause significant yield losses, making early management of winter annuals important. These weeds germinate in late summer or fall, overwinter as seedlings or rosettes and resume growth early in spring. Dense patches can complicate planting, compete for moisture and nutrients and replenish the weed seedbank.
Some common weeds in soybean fields can also host soybean cyst nematode (SCN). That makes fall weed control more than a field-cleanup practice. Identifying and controlling species such as purple deadnettle, henbit and field pennycress can remove living hosts that allow SCN to persist or reproduce between soybean crops, strengthening an integrated SCN management program.¹
How soybean cyst nematode and winter annual weeds are connected
Soybean cyst nematode does not need winter annual weeds to survive between soybean crops. Its eggs can remain protected inside cysts in the soil. However, certain winter annual weeds in soybean provide living roots that SCN can infect, potentially allowing the nematode to reproduce when soybeans are not growing.
Six common winter annual weeds in soybeans have been identified as SCN hosts:
- Purple deadnettle
- Henbit
- Field pennycress
- Shepherd’s purse
- Small-flowered bittercress
- Common chickweed
Purple deadnettle and henbit are considered the strongest hosts. Greenhouse research found that both supported SCN populations comparable to or greater than those found on SCN-susceptible soybeans.²
Controlling these weeds will not eliminate SCN, but removing alternative hosts can help limit additional reproduction and strengthen a broader management program.
Control strategies for winter annual weeds in soybeans
Many weeds look similar from afar, but their control methods vary. Learning how to properly identify these SCN hosts is critical.
Here are the characteristics to look for when scouting these SCN hosts:
Purple deadnettle
One of the strongest hosts for soybean cyst nematode, purple deadnettle has square, hairy stems, reddish-purple upper leaves and reddish-purple upper and lower leaf petioles.
Henbit
Like purple deadnettle, henbit is a strong host for SCN. Both have square stems, slightly hairy egg-shaped leaves and small purple flowers nestled in the upper leaves. However, unlike purple deadnettle, henbit has petioles on the lower leaves but not on the upper leaves.
Field pennycress
Field pennycress is considered a moderately strong host for soybean cyst nematode. It begins as a light-green rosette and develops round, notched seedpods.
Shepherd’s purse
Shepherd’s purse is a relatively weak host for soybean cyst nematode. It has deeply lobed leaves and heart-shaped pods.
Small-flowered bittercress
Similar in appearance to field pennycress and shepherd’s purse, small-flowered bittercress is a weak yet feasible host for soybean cyst nematode. It has oval leaflets and long, narrow pods.
Common chickweed
Even though it is a relatively weak host for SCN, common chickweed cannot be overlooked as a winter annual that can harbor SCN. It grows low with branching stems and a single row of hairs.
Winter weed control options
Understanding how to scout for and properly identify winter annual weeds is critical. As already noted, though many winter annual weeds may share similar physical features, methods for controlling them often differ.
Apply fall burndown to remove SCN hosts
Scout after harvest and target emerged winter annuals while they are small, green and actively growing. Fall burndown can prevent seed production, reduce spring biomass and remove living roots that may support additional SCN reproduction. Sharpen® herbicide provides broad-spectrum burndown of broadleaf weeds while Verdict® herbicide may fit preplant or preemergence programs.
Consider tillage and the complete SCN program
No-till and reduced-till fields require close scouting because winter annuals are not disrupted by tillage. Tillage may suppress emerged weeds, but it can also move SCN-infested soil within a field.³
Regardless of production system, combine winter annual weed control with soil testing, resistant soybean varieties and nonhost crop rotation. Always read and follow label directions.
Experts are available to help you with your weed control and SCN management decisions. Reach out to your seed retailer, a nearby extension office agent or a seed company professional like your regional BASF representative.
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Endnotes
- Basnet, Pawan, et al. “Reproduction of Soybean Cyst Nematode Populations on Field Pennycress, Henbit, and Purple Deadnettle Weed Hosts.” Agronomy, vol. 12, no. 9, 2022, article 2027. doi:10.3390/agronomy12092027. www.openprairie.sdstate.edu/plant_faculty_pubs/386
- Mock, Valerie A., et al. “Winter Annual Weeds and Soybean Cyst Nematode Management.” Purdue Extension, www.extension.purdue.edu/extmedia/ws/ws-36.pdf.
- Chen, Senyu, et al. “Soybean Cyst Nematode Management Guide.” University of Minnesota Extension, reviewed 2021,https://extension.umn.edu/soybean-pest-management/soybean-cyst-nematode-management-guide.
