Fall Control of a Red Clover Cover Crop

042913_2028_HaveILostAn2I have had some questions about red clover cover crops, when to kill it off and what is the best method to kill the clover.  A good stand of red clover can provide as much as 65 lb. of N per acre for next year’s corn crop as well as help dry the soil in the spring by “pumping” moisture out of the soil. However, this may take a while and delay spring land work and planting.  Proper timing and control in the fall is important to optimize your time in the spring.  The following information is from Mike Cowbrough at OMAFRA.

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 short changing your nitrogen credit for next spring.

Managing options for red clover

Fall plowing is the only effective tillage operation for managing red clover. If your preference is to use less aggressive tillage (e.g. chisel plow) or no-till, then a herbicide burndown is needed. Research conducted by the University of Guelph has consistently shown that the best and most cost effective herbicide for controlling red clover is dicamba (e.g. Banvel II, Oracle, Hawkeye) applied at 250 mL/ac. 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.

Can I Reduce the Rate of Dicamba or Use 2,4-D Instead?

When dicamba rates were reduced to 300 mL/ha (125 mL/ac), red clover control was unacceptable.  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 has not significant improved control of red clover when compared to glyphosate alone. 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.

Red Clover Control and relative cost of various fall management strategies.

Treatment

Rate/ac

Control

dicamba

250 mL

99%

glyphosate (540 g/L)

+ dicamba

500 mL

+ 250 mL

99%

fall plough

95%

amitrol

1670 mL

90%

glyphosate (540 g/L)

+ amitrol

500 mL

+ 1000 mL

90%

glyphosate (540 g/L)

1.34 L

85%

2,4-D Ester (700 g/L)

500 mL

65%

Source: Dr. Peter Sikkema, Dr. Clarence Swanton and Dr. François Tardif
* Control evaluated in April following the fall applications

What about Volunteer Wheat?

Since dicamba won’t control any volunteer wheat, glyphosate will need to be tank-mixed. The lowest labeled rate of a glyphosate 540 g/L concentration (i.e. Roundup Weathermax) that can be tank-mixed with dicamba for the control of volunteer cereals is 0.5 L/ac.