A:   Controlling broadleaf weeds in grass-alfalfa pastures can be challenging. There are a few options available that can provide some level of control. The commonly used herbicide, 2,4-D, would be very effective on many annual weeds that appear in irrigated pastures, such as marestail, lambsquarters, pigweed, and mustards. But as you are aware, this could result in some damage to the alfalfa. I have seen some producers use lighter rates of 2,4-D in mid to late May and have reported good weed control with only moderate damage to the alfalfa and most of the alfalfa did recover. However, this can be risky for the alfalfa. Timing of the herbicide application is important, aiming for when the weeds are small. For severe annual and perennial weed infestations, another option can be to use full rates of the herbicide with the intention that the alfalfa may have to be reseeded. It can be interseeded into grass pastures and will re-establish fairly easily. There are 2 herbicides, Butyrac and Butoxone (2,4-DB), that are formulated to control broadleaf weeds in grass-alfalfa mixtures and will have little or no effect on the alfalfa. However, there is a 60 day restriction on using the forage. Other management factors that can help reduce weed populations include maintaining a strong grass stand. This would be associated with the irrigation and fertility management and rotational grazing where about 5 to 6 inches of residual stubble height is left in a paddock for quick regrowth.