A beautiful stand of red clover can provide as much as 75 kg of nitrogen per hectare (when at 40 cm tall) for next years corn crop. However, if the clover crop is not “killed off” in the fall, then preparing a suitable seedbed to plant next years crop in is often significantly delayed resulting in reduced yields. A review of different strategies to control red clover in the fall are presented below.
When is the best time to retire the red clover stand?
A research project conducted by Dr. Steve Bowley (University of Guelph) demonstrated that red clover gains significant root biomass during the month of October. Therefore killing off the stand in September could be shorting your nitrogen credit for next spring.
Managing options for red clover
Tillage: Fall plowing is the only effective tillage operation for managing red clover (Figure 1). If your preference is to use less aggressive tillage (e.g. chisel plow – Figure 2) or no-till, then a herbicide burndown is needed.
Herbicides: Two studies have evaluated red clover control in the fall and are summarized in Tables 1 and 2. Research conducted by the University of Guelph has consistently shown that the best and most cost effective active ingredient for controlling red clover is dicamba (e.g. Engenia, Xtendimax) applied at 500 mL/ha (or 200 mL/ac – refer to Figure 3). Glyphosate + Distinct (dicamba/diflufenzopyr) has also provided excellent control of red clover (Figure 7). The application timing of dicamba in many of these trials has gone into to mid- to late-October. This is also an opportune time to manage perennial weeds (using a glyphosate + dicamba tank-mix). The key is to ensure that the air temperature at application is greater than 10 ºC, and that the nighttime temperature after application stays ideally at 5 ºC or greater.
Table 1. Red Clover control (% visible) the following spring after fall applied treatments at the Elora Research Station
| Treatment | Rate | Control |
|---|---|---|
| dicamba (600 g/L) (e.g. Engenia) | 0.5 L/ha (0.2 L/acre) | 99% |
| glyphosate (540 g/L) + dicamba (600 g/L) | 1.25 L/ha + 0.5 L/ha (0.5 L/acre + 0.2 L/acre) | 99% |
| fall moldboard plough | 95% | |
| glyphosate (540 g/L) | 3.35L/ha (1.34 L/acre) | 85% |
| glyphosate (540 g/L) + 2,4-D ester 700 (660 g/L) | 1.67 L/ha + 1.25 L/ha (0.67 L/acre + 0.5 L/acre) | 70% |
| chisel plough | 65% | |
| 2,4-D ester 700 (660 g/L) | 1.25 L/ha (0.5 L/acre) | 65% |
Table 2. Red Clover control (% visible) the following spring after fall applied treatments at Ridgetown and Huron Park Research Stations.
| Treatment | Rate | Control |
|---|---|---|
| glyphosate (540 g/L) + Distinct | 1.67 L/ha + 288 g/ha (0.67 L/acre + 115 g/acre) | 96% |
| glyphosate (540 g/L) + dicamba (600 g/L) | 1.67 L/ha + 0.5 L/ha (0.67 L/acre + 0.2 L/acre) | 93% |
| glyphosate (540 g/L) | 3.35L/ha (1.34 L/acre) | 75% |
| glyphosate (540 g/L) + 2,4-D ester 700 (660 g/L) | 1.67 L/ha + 1.25 L/ha (0.67 L/acre + 0.5 L/acre) | 72% |
| glyphosate (540 g/L) | 2.5L/ha (1 L/acre) | 70% |
| glyphosate (540 g/L) | 1.67 L/ha (0.67 L/acre) | 62% |
Can I Reduce the Rate of Dicamba or Use 2,4-D Instead?
When dicamba (600 g/L) rates were reduced to 250 mL/ha (100 mL/ac), red clover control was unacceptable (refer to Figure 4). 2,4-D (660 g/L) has been inconsistent in recent public trials when applied alone at 1.25 L/ha (500 mL/ac). The addition of 2,4-D to glyphosate (Figure 6) has not significantly improved control of red clover when compared to glyphosate alone (Figure 5). However, over a decade ago, Dr. Clarence Swanton (University of Guelph) observed effective control of red clover with fall applications of glyphosate + 2,4-D. A possible explanation for the difference in red clover control between studies is that a non-ionic surfactant at 0.5% v/v was added to the glyphosate + 2,4-D tank-mix in the Swanton research, whereas it was not included with any of the trials summarized in tables 1 and 2.
