Pennyroyal is mainly a weed of moist pastures and turf, although it can tolerate some summer dryness. It is often not noticed until summer when conditions can be quite dry as this is when it flowers most prolifically, making it very noticeable. The other noticeable thing about pennyroyal is the strong smell of mint given off from the foliage when it is crushed or cut. This mat-forming species is normally not wanted in turf. Likewise, in pastures livestock are not keen to eat it, so it can begin to dominate the pasture if soil conditions are moist enough to allow it to do so. If lactating cows do eat this weed, milk tainting can occur.
Pennyroyal is a perennial weed, it has creeping stems with roots along them to hold it tightly to the ground. I forms dense mats of vegetation within pastures and lawns. When it is flowering, the flowers are quite distinctive, with purplish- blue flowers clustered around the base of the leaves.
In pastures, we find that 24-D is effective with 60-70 % control. However this should be applied during spring or autumn when the weed is actively growing, not it summer when it is very visible due to the flowering but not necessarily growing very actively.
For spot treatment Tordon Brushkiller will provide good control when applied through a knapsack.