Green Dragon, please do some reading about the Knotweeds before you waste your time trying to 'mulch' it to death. This plant can push up through asphalt. It spreads by rhizomes(it has no taproot)that are far reaching. Any piece left on the ground or in a compost pile can root. Plants need to be cut back to prevent flowering/seeding while your trying to deal with it. It grows extremely fast. Whatever method you choose, it will take perseverance. Here is a link that might be useful: one of many info sites

You might need to examine the seat switch just to make sure it is not activating when you lean in the seat or hit bumps. It could be a loose connector on the seat switch or even a broken wire there.

I'm totally against herbicides,on principal. The D##NED things are apparently working their way into food crops by now,and there just is no need for them. My woodland /wild "garden" is full of some of the worst plant thugs known to man: brambles, vitalba, ginestra (broom)...in comparison to these ,the weedy trees are like petunias , lol. All you have to do is cut them level with soil and cover the offenders with cardboard,and put mulch on top of it. If it's really bad, use several layers of cardboard. If it's really, really bad,use black plastic. Roses are extremely sensitive to herbicides, but in any case, these things-herbicides- are poisons,and we don't want to be spreading about more poison in our world,now, do we? No, we don't.

It looks exactly like St. Augustine to me. It also looks like you need to sharpen your mower blade - those blades are torn pretty bad.