Don't know what zone you're in, but in most northern zones at least, I think
the UW-Extension recommendation should apply: Treat for crabgrass with a
preemergent product when the forsythia are in full bloom. Around these
parts (Zone 5), that should take into account the soil temp, which is the
critical point at which the crabgrass seed is ready to germinate.

"Play4abuck" wrote in message
news:xNj2e.11192$jX6.10595@okepread02...
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I bet this is an annual question. I think I have been applying mine to
early, usually after my grass has started to grow and I have mowed it once
or twice.

Here is what I found during my quest for knowledge today! I was hoping to
find a straight forward answer, like some soil temp, but even that advice
varies.

-Start taking your lawn soil's temperature early in the morning. When it
reaches 55 degrees, apply crabgrass preventer.

-Apply crabgrass preventer as soon as established tall fescue and Kentucky
bluegrass lawns green up and start growing well.

-Crabgrass preventer halts the seed-sprouting process. If applied after
this
year's crabgrass germinates, it will have no effect. The only exception to
this rule is a rather new product - dithiopyr - sold in a
herbicide-fertilizer mix called Dimension.

-Apply when temperatures reach around 70 degrees for a consistant period
of
time, typically for more than 2 or three days.

-Apply in early spring before weeds sprout (before temperatures are
regularly in the 80's).

-When the forsythia bushes starting to flower, or the redbud trees start
to
bud, or before the dandelion weed puffs and spreads. (Hell, I don't have
any of these in my yard!)

Anyone want to add their $.02?

Cheers,
Jim