Around this time of year, I always see a large number of pastures being mowed for weed control, not hay production. Have you ever stopped to think about what it costs to mow a pasture? Mowing is costly, and pastures that have weed problems this late in the growing season have no chance for optimum weed control.
The following table shows the cost of mowing versus applying herbicides. All herbicide treatments except Grazon P+D are more economic than mowing. However, Grazon P+D is the only herbicide listed that offers significant residual weed control, which is worth the additional cost when weed infestations are severe.
The majority of pasture weeds are annual broadleaf species that can easily be controlled in the spring with a single herbicide application. A timely application of 2,4-D amine or a Banvel and 2,4-D tank mix controls annual weeds before they have time to reproduce or, more important, compete with your warm-season forage. Eliminating weed competition for nutrients and moisture in the spring is critical, since over 60 percent of the summer's forage is produced from May through June. Mowing does not stop weed competition through the spring and will not stop weeds from producing seed. Even after being mowed, the cut plant can finish its life cycle and produce viable seed. Mowing in the summer is for aesthetics only. It does nothing to enhance forage production. Weed competition has already done its damage, and by late June a majority of pasture weeds are mature. Mowing tops the valuable forage, taking the most nutritious portion of the plant.
I do not recommend an annual herbicide application. Herbicides should be applied to get a handle on a weed problem in the spring. Typically, with good soil fertility and grazing management programs, weed populations decrease over time. Providing sufficient levels of fertility while maintaining a forage stubble height of at least 3 inches in introduced pastures produces grass. Applying herbicides controls weeds; it does not produce grass. Concentrating inputs on forage production and grazing management instead of weed control will produce a greater return for your investment.