It looks like crab grass from here. This is an annual grass with broad, ugly
blades that tends to sprawl out like the arms of a crab and look like hell.
Most weed chemicals designed for lawns are specific to killing broadleaf
plants (dicotyledons), because most weeds are dicots while grass is a
monocotyledon and thus unaffected by this type of poison. The problem with
crab grass is it is a monocot, not a dicot (being just another species of
grass), so will not be killed by these chemicals. On the other hand, if you
use grass-killing chemicals, they will kill not only the crab grass but also
the desired lawn grass.
Crab grass has to be controlled with a pre-emergent chemical that kills the
seeds. This works by killing only seeds, not adult plants. Since crab grass
is an annual, it has to come up from seed fresh each year. You have to put
down the crab grass killer prior to the sprouting of the seeds, i.e. in very
late winter. Once they have sprouted it's too late.
For this year you could get a spray bottle of grass killer and spot spray
the individual crab grass plants, but this is going to be a lot of work
judging from the number of them you have in the photos. Or you could put
down a broad-spectrum like Roundup that kills everything, then replant the
entire lawn with new grass seed. It takes surprisingly little time to get a
fully mature lawn this way -- with water, sun, and warm weather, it can take
as little as six weeks from the time you plant to the time the new lawn is
mature. (If you go for sod it will be much more expensive, and half of it
will probably die anyway.)
Utopia in Decay -- The future is coming to get you.
I have a major problem controlling this trouble weed on my backyard.
I have sprayed the whole area with the liquid weed control I bought at
my local Home Depot two times but it did not appear to work. Perhaps,
I did not use the right one.
Could some body help me indentify the type of weed and hopefully
advise me what kind of weed control I should use.
Thanks in advance,
Here are link to the images I took: