One of the activities for the chapter on weed ecology was the following:
"Visit your lawn. Choose three weeds and identify. After you've identified them, discuss the implications of these weeds in your lawn. Now visit the edges of your lawn, perhaps in the food garden bed or your ornamental plant beds. Find three weeds there and identify. Are they the same as the lawn weeds you saw? How do you manage these weeds in both situations (lawn and other)?"
I would say the main problem weed in my back yard is Florida betony (cool-season perennial). When we first bought our house, I didn't know what it was. In the summer, digging in the ground, I would find these white tubers - I didn't put the two together at the time. For some reason they are almost exclusively in my back yard, so I don't do too much with them. Since I know they are perennials and grow from those white tubers, pre-emergent herbicides will not work. After doing some research on control methods, it appears there are a couple of post-emergent herbicides that will work, depending upon your grass type. I have a good bit of bahiagrass in the back yard - which, to me, is a weed in itself - so I mostly leave it alone. It take a different approach when it comes up in my garden. When I see the tubers I get rid of them, and I tend to hand-pull the shoots when I see them, hoping that, if I pull them enough times, it will exhaust the plant.
I used to have dollar weed (warm-season perennial) around my vegetable garden, but I was very vigilant about pulling it up overtime I saw it. It's not a problem anymore. It became a problem in one of our landscaped beds out front, but it was easy to get rid of. The stolons were growing in the top layer - mulch/compost, and it was easy to hand-pull. Long strings of it came up out of the loose mulch. I notice from the photo that it's in the turf as well, but I can tolerate that.
I've been pulling up spurge around our vegetable garden all summer. It's a warm-season annual that I've begun to notice a lot this year. It grow outward from a taproot, hugging the ground. It looks like it covers a large area, but all you have to do is pull it up from the single root and it's all gone.
The past year or so, I've gotten a little purslane in our vegetable garden. I was curious about it, because it have very succulent stems and leaves. It's a warm-season annual related to Portaluca. Like other weeds in my garden, I try to hand pull weed now - since I Roundup-ed my pole beans last summer!
There is another plant that resembles dollar weed, that I believe I have in my yard as well. It's called dichondra and it must get confused with the other because it's mentioned in the dollar weed article on the HGIC website. From what I've seen, it is more of a clumping type of plant. I could be wrong.
There were other weeds I could mention, but these were the ones I knew the most about. I'm sure a lot of people know what this weed is in the photo - I'm am just drawing the biggest blank. I'll post the answer when someone tells me on the message board, but until then, I'll be in the dark. Comment, if you think you know!