Pre-emergent works by stopping germination. It needs to be in place
by late April, generally before the 2nd or 3rd mowing. After that
it's too late.

Once the plants are established, the most effective treatment is
Aclaim, but it's not available as a retail product. The arsenic based
crabgrass killers sold retail take a couple applications to kill the
crabgrass and usually wind up killing grass too.



Dave in The Ozarks wrote in message . ..
I understand that Crabgrass Preventives are supposed to be applied in
early Spring and that they work by sealing the soil surface so that
the seeds don't germinate.

I live in the SW corner of Missouri. My lawn is a mix of
fescue/bluegrass/rye. I applied Scotts with Halts in the spring. No
crabgrass had come up until the last 2 or 3 weeks - Now there is quite
a lot of it. Now I'm applying Weed B Gone crabgrass killer to it,
but that weems to really weaken and even thin the other grass.

Can pre-emergent like Scott w/Halts be applied later in the season?
If I applied it in early June would it prevent emergence in June and
July?

Thanks,
Dave in the Ozarks