Figure 1: Purple deadnettle in a wheat field — October 2018 at a yield-reducing population density of around 500 plants per square metre.
Photo: Supplied
Figure 2: The ideal stage of purple deadnettle to maximize control with post-emergence herbicides. Photo taken in late September 2018.
Photo: Supplied
Figure 3: Purple deadnettle on May 2, 2019, that is flowering and beyond the growth stage whereby it could be successfully controlled with herbicides.
Photo: Supplied
Figure 4: Purple deadnettle flowering on May 18, 2019, in the unsprayed control plot.
Photo: Supplied
Figure 5: Purple deadnettle control with a pre-plant application of Eragon LQ + Merge (right) compared to the unsprayed control (left).
Photo: Supplied
Figure 6: Purple deadnettle control with a post emergent application of Refine SG + Agral 90 (left) compared to the unsprayed control (right).
Photo: Supplied
Figure 7: Purple deadnettle control with a post-emergent application of Infinity (left) compared to the unsprayed control (right).
Photo: Supplied
Figure 8: Purple deadnettle seedlings at time of post-emergent application. Notice the large range in size.
Photo: Supplied
Q: I’m seeing more henbit and/or purple deadnettle in my winter wheat crop. Should it be controlled, and how?
A: Henbit and purple deadnettle are often discussed interchangeably 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 spring). Both are hosts to soybean cyst nematodes1 and yield losses of up to 38 per cent have been documented at dense populations (e.g. 155 plants per square metre)2. Most published research evaluating herbicide efficacy has been done on henbit.
Last fall, I evaluated purple deadnettle efficacy with common fall-applied herbicides in winter wheat.
Control of henbit is better with fall-applied herbicides compared to spring. Since most seedlings emerge in fall, it makes sense that herbicides would work better when applied to small seedlings. A Kansas study found a 30 per cent improvement in henbit control with fall-applied herbicides compared to the spring3. A Nebraska study demonstrated the rate of Eragon LQ + Merge had to be doubled in spring to achieve the same level of henbit control achieved with a fall application4.
Effective herbicides:
A Kansas study with Simplicity herbicide (pyroxsulam) provided 80 per cent control when applied to henbit in the fall, but only 49 per cent when spring-applied3. A Kentucky study found that Infinity (pyrasulfotole/bromoxynil) and Refine SG (tribenuron/thifensulfuron) provided greater than 95 per cent visual control of henbit when applied in the fall5. Eragon LQ (saflufenacil) provided greater than 90 per cent control of henbit in studies conducted in Nebraska4.
When I was asked to investigate herbicide effectiveness at controlling purple deadnettle, I couldn’t find anything in the scientific literature, so I focused on herbicides that have been cited as effective on henbit (since both species are from the same genus). The table outlines the herbicides used, application timing, rate and level of control.
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 efficacy was not above 80 per cent 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’s 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.
Application notes:
- 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: two leaf to five to 10 cm tall (Figure 8).
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 Stevan Z. Knezevic, Avishek Datta, Jon Scott, Leo D. Charvat, 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 and Soil Sciences Department, University of Kentucky, Princeton, KY 42445. Accessed May 20, 2019, at wheatscience.ca.uky.edu/sites/wheatscience.ca.uky.edu/files/rr07-08pg40.pdf.
Have a question you want answered? Hashtag #PestPatrol on Twitter to @cowbrough or email Mike at [email protected].
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