Question:  My dog, a 50 lb. border collie ate/eats lantana leaves.  I dug it out, but more pops up.  To date, over several years, no ill-effects.  Do I induce vomiting or is this only when seeds are available and consumed.  Is toxicity an issue?  Literature and vets give mixed and/or limited information.  Not clear if toxic to canines.  Does it take large amounts such as with farm animals who graze?
Answer:  Nobody really seems to know why dogs go outside and eat plants, or why they choose the plants that they do.  I personally think it's just an enjoyable thing for them, much like we graze the cookie jar.  Although eating lantana has been known to kill livestock in rare instances, it is important to know that they had to eat a LOT of this plant to get sick enough to die from it.  I think the ratio is like 1% of body weight for any toxicity to occur.  So, your 50 pound dog would have to eat a half pound or more of lantana to get really sick, which isn't likely.  You say it has been there a long time and he's still alive with no ill-effects, so I wouldn't worry about it too much.  The unripe green berries are the most poisonous part, but again, it's doubtful that there would be enough to do him any real harm, assuming he doesn't avoid them altogether, which he probably does. One way to be sure he doesn't get the seeds is to just deadhead the flowers as they fade so the plant won't produce any seed.  Another is to just keep at it until you have removed the plant entirely from his grazing grounds.  If you pull it every time you see it spring up, it will eventually give up the ghost and die off.  As far as toxicity, again, he would have to eat a lot of the stuff for it to build up over time and become chronically toxic, so I don't think he is in any danger from that.  In the end, if it bothers you enough that he is eating it, you should get rid of it, but I don't think he is in any mortal danger from the small amount you describe.

Question:  Recently I had to be gone from my home for a extended period of time. My lantana has flourished beyond its boundaries -  this is its second season of growth. The first year it was fantastic and this year it is even more beautiful.  The only problem is I live in a town with sidewalks and it is beginning to hang over or over grow on the sidewalk. My question to you is will it kill my lantana if I trim it back to its boundaries?
Answer:  Go ahead and trim the Lantana as much as you need to.  If you want more plants, use this opportunity to root some cuttings by sticking the trimmings in some potting soil in flats or pots, keep moist in the shade, and let them take root - it takes Lantana maybe 2-3 weeks to take root and start putting out new growth from cuttings.  I had the exact same problem and just trimmed mine back the other day and it looks so much better.  It won't hurt the plant at all, so trim as hard as you need to to make it look good again.