Q: I’m seeing more henbit and/or purple deadnettle in my winter wheat crop? Should it be controlled and what can be done to control it?
A: Both henbit and purple deadnettle are two weeds often discussed inter-changeably because they look similar, are from the same genus (Lamium) and have similar emergence patterns (mainly in the fall, but henbit will also emerge in the spring). Both species are hosts to soybean cysts nematodes1 and yield losses of as much as 38% have been documented at dense populations (e.g. 155 plants per square metre)2. Most of the published research evaluating herbicide efficacy has been done on henbit. In the fall of 2018, I evaluated purple deadnettle efficacy with common fall applied herbicides in winter wheat.
Control of purple deadnettle or henbit is better when herbicides are applied in the fall compared to the spring. Since most seedlings emerge in the fall it makes sense that herbicides would work better when applied to small seedlings and a couple of North American studies demonstrate this. A Kansas study found a 30% improvement in henbit control when herbicides were applied in the fall compared to the spring3. A Nebraska study demonstrated that the rate of Eragon LQ + Merge had to be doubled in the spring to achieve the same level of henbit control that was achieved with a fall application4.
Figure 3: Purple deadnettle on May 2nd, 2019 that is flowering and beyond the growth stage whereby it could be successfully controlled with herbicides.
What herbicides are effective? Simplicity herbicide (pyroxsulam) in a Kansas study provided 80% control when applied to henbit in the fall, but offered 49% when applied in the spring3. A Kentucky study found that both Infinity (pyrasulfotole/bromoxynil) and Refine SG (tribenuron/thifensulfuron) provided over 95% visual control of henbit when applied in the fall5. Lastly, Eragon LQ (saflufenacil) provided over 90% control of henbit in studies conducted in Nebraska4.
Control of purple deadnettle in one Ontario study: When I was asked to investigate herbicide effectiveness at controlling purple deadnettle, since I could not find anything in the scientific literature, I decided to focus on herbicides that have been cited as being effective on henbit since both species are from the same genus. Table 1 outlines the herbicides used, application timing, rate and level of control.
Table 1. Herbicide, application timing, rate used and visual control the following spring after application.
| Herbicide | Application Timing | Rate | % Control |
| Eragon LQ + Merge | Pre-plant | 59 mL/acre + 400 mL/acre | 90 |
| Infinity | POST | 330 mL/acre | 70 |
| Refine SG + Agral 90 | POST | 12 g/acre + 0.2% v/v | 70 |
Pre-Plant Application: September 28, 2018. air temperature: 11°C
Post-emergent Application October 26th, 2018, air temperature: 1°C
Weed stage at post-emergent applications: 2 leaf to 5-10 cm tall (Figure 8)
Figure 8: Purple deadnettle seedlings at time of post-emergent application, notice the large range in size.
Bottom Line: Based on limited data of only one trial during one field season, the pre-plant application of Eragon LQ + Merge provided the best control of purple deadnettle. Both Infinity and Refine SG + Agral 90 suppressed growth of purple deadnettle, but the efficacy was not above 80% visual control. Poorer control with Infinity and Refine SG compared to other reports could be attributed to cool air temperatures that occurred at and following application. It is possible that Eragon LQ provided better control of purple deadnettle than Infinity or Refine SG because the seedling plants were smaller and the air temperature higher at the time of application.
Citations:
1 J. Earl Creech, Jared S. Webb, Bryan G. Young, Jason P. Bond, S. Kent Harrison, Virginia R. Ferris, Jamal Faghihi, Andreas Westphal and William G. Johnson 2007. Development of Soybean Cyst Nematode on Henbit (Lamium amplexicaule) and Purple Deadnettle (Lamium purpureum) Weed Technology, 21:1064-1070.
2 Shawn P. Conley and Kevin W. Bradley. 2005. Wheat (Triticum aestivum) Yield Response to Henbit (Lamium amplexicaule) Interference and Simulated Winterkill. Weed Technology, 19:902-906.
3 Seshadri S. Reddy *, Phillip W. Stahlman and Patrick W. Geier. 2013. Downy Brome (Bromus tectorum L.) and Broadleaf Weed Control in Winter Wheat with Acetolactate Synthase-Inhibiting Herbicides. Agronomy: 3, 340-348.
4 Knezevic, Stevan Z. ; Datta, Avishek ; Scott, Jon ; Charvat, Leo D. 2010. Application timing and adjuvant type affected saflufenacil efficacy on selected broadleaf weeds
Crop Protection, 29(1): 94-99.
5 James Martin, Charles Tutt, and Dottie Call. HERBICIDE EVALUATION OF HENBIT CONTROL IN NO-TILL WHEAT . Plant & Soil Sciences Department, University of Kentucky, Princeton, KY 42445. Accessed May 20, 2019 at https://wheatscience.ca.uky.edu/sites/wheatscience.ca.uky.edu/files/rr07-08pg40.pdf