I have shining geranium in a 5 Acre wooded horse pasture. It is covering approximately 1/4- 1/3 of the pasture. How do you recommend getting rid of it? My neighbor has honey bees and is concerned about chemical impact on the bees. Thank you!
As you have noticed, it is aggressive and can quickly take over an area.
This species is a winter annual which means plants emerge in fall and grow throughout the spring. You'll want to get a jump on this now, ideally before flowers set seed, because seed shed - although entertaining with it's forceful ejection mechanism! - greatly worsens the problem.
If chemical control is needed, one possibility is Escort XP (metsulfuron), another is triclopyr, both are registered for use in small pastures to control broadleaf weeds. The addition of a surfactant will help efficacy of the herbicides.
Spraying at sundown is a good tactic to reduce bee exposure.
I highly recommend consulting section W.1 of the PNW weed management handbook, it is written by a much better expert on the topic than myself, and has some very helpful tips. Here is a link to that document: https://pnwhandbooks.org/weed/pasture-rangeland/small-pastures
Good luck and thanks for using Ask-an-Expert,