Wheat Stubble Weeds and Red Clover

"Cheap nitrogen" seems like an oxymoron, unless you have a nice stand of red clover following wheat harvest. The challenge becomes getting as much growth, and therefore soil nitrate next spring from that red clover, while managing weeds, volunteer wheat and ultimately the red clover. Failure to do so will negatively impact planting, establishment and the yield for next year's corn crop.

Managing the Red Clover

Fall plowing is the only effective tillage operation for managing red clover. If your preference is to use less aggressive tillage 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 (i.e. Banvel II or Oracle) at 250 mL/ac (refer to Figure 1). 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 + Banvel II 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?

No. When dicamba rates were reduced to 125 mL/ac, red clover control was unacceptable (refer tp Figure 2). 2,4-D (660 g/L) has never provided control of red clover in pubic research trials when applied at 500 mL/ac.

Table 1. Red Clover Control and relative cost of various fall management strategies.

Source: Dr. Peter Sikkema, Dr. Clarence Swanton and Dr. François Tardif
* Control evaluated in April following the fall applications
** Relative to the Average cost (100) of all treatments in Table 1.

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.

Managing Annual Weeds

Annual weeds will typically start to flower and set seed very shortly after wheat harvest. Some producers have successfully "clipped" the red clover to cut off the flowering annual weeds. The red clover then grows back and provides a cover that reduces the amount of annual weed re-growth and germination of new plants. Failing that, the next step would be a tillage pass or herbicide application to manage both. So you will have to make a decision. Do you want to minimize weed seed return (i.e. manage now) or do you want to maximize red clover growth (i.e. manage late September, October)?

Figure 1. Red clover control in April with dicamba applied in late October at 250 mL/ac.

Figure 2. Red clover control in April with dicamba applied in late October at 125 mL/ac.

Figure 3. Red clover control in April with 2,4-D Ester applied in late October at 500 mL/ac.