Chickweed. Pull it out before it sets seed. Which it will do any minute now.

Thanks for the reply. It's all over the back yard and too much to pull but I'll find something that will kill it now that I know what it is.

Mowing it should help. It needs bare ground so if the grass is thick and you keep mowing before it flowers you should be able to control it. Any broadleaf chemical which will kill it will also kill any other plants apart from grass. Even if you kill these plants there will be a seed bank in the soil so more will grow.

Thanks for the extra info! I was doing a little research and it seems besides trying to deal with it now I should also do something in the fall and next spring to keep the seeds that drop from emerging.

Really you need to be weeding year round. It's not a once and for all or even twice and got all thing. Chickweed can grow, flower and set seed in a couple of weeks so the best way to get on top of it is to keep after it all the time for a year or so. Once you've slowed its progress it will gradually become easier as the seed bank depletes. The old saw 'one year's seeding, seven years weeding' is not far wrong.

In your lawn, any good chickweed killer that's compatible with your grass type will work. For northern lawns, Weed B Gon Clover, Chickweed, and Oxalis works fine.

In the garden...not so much. Hand pull where possible. Spot spray where possible. For spot sprays, you can use WBG like the above or a wide-spectrum weed killer.

In both cases, if you don't plan to seed, you can use a pre-emergent on the lawn and gardens to slowly exhaust that seed bank and keep the chickweed down without having to re-spray a harsher weed killer.

Personally, I use Prodiamine yearly on the gardens (I start seed indoors under lights and transplant seedlings in early May when frost is long over) and in fall in the lawn (to suppress out P. trivialis and P. annua in my case). But there are tons of pre-emergents that work really well on chickweed.

If you do plan to seed (and never seed the lawn in spring anyway, wait until fall) use Dimension in early spring to suppress out weed sprout at the 2-3 month rate. It's actually a little late in many areas, but it'll do some good and at least stop crabgrass...

Oh my! Based on your last msg I think you have issues with watering, mowing, and fertilizing. You may have more fundamental issues, but we need more information to put a fine point on them.

Where do you live?

What kind of grass do you have?

How often and for how long do you water?

When were the last 2 times you used fertilizer, and what did you use?