Although the best time of year to apply herbicides for the control of broadleaf weeds is during the fall, most people are not willing to wait that long in order to treat for weeds, especially once dandelions begin to emerge and produce their familiar yellow flower. If spring applications of herbicides are going to be made for control of perennial broadleaf weeds, such as dandelion, white clover, and plantain, it is best to target the herbicide application when the plants are extremely young. For that reason, you may notice yard services applying broadleaf herbicides in the next few weeks, even if you don't yet see a sea of yellow blossoms in the turf.
Control of broadleaf weeds is most often accomplished with a three-way combination of the herbicides 2,4-D, 2,4-DP, MCPA, MCPP, triclopyr, clopyralid, and dicamba. 2,4-D, MCPA, and triclopyr are generally more effective on dandelions, while 2,4-DP, MCPP, and clopyralid are more effective on clovers. Dicamba is better for difficult broadleaves such as thistles. Usually a three-way herbicide will have 1 or 2 compounds from each grouping (e.g. 2,4-D, MCPP, and dicamba). Ester formulations are generally more effective at this time of year. However, as temperatures warm (above 60-70 degrees) volatility of esters results in a drift hazard and so amine formulations become more appropriate choices. New this year from PBI Gordon are broadleaf herbicide combinations with a herbicide called carfentrazone, which is reported to result in faster burndown of the targeted weeds. There are also options for preemergent control of broadleaf weeds (check the labels for Gallery ¥, Dimension ¥, pendimethalin, Barricade ¥, and Ronstar ¥). Remember, though, that preemergent herbicides are for control of annual broadleaf weeds (such as pigweed, spurge, oxalis, and knotweed) and will not result in good control of perennials.