When do I apply preemergence weed killer to my lawn?

Scott's sells a fertilizer with HALTS, a preemergent treatment. The label says to treat the lawn when the ground temperature reaches 65 degrees. Since most people do not measure ground temperature, the label says to apply in the spring when the forsythia blooms. Near Chicago, where I live, forsythia blooms fairly consistently in early to mid April. I have been advised by some that this is too early to apply preemergent treatments. In my experience, however, it is better to apply too early as opposed to too late - once the seeds from last year's crop of a widespread crabgrass infestation germinate, you are done. Several other sources cite a ground temperature of 55 - 60 degrees for applying preemergent treatments, supporting my "better earlier than later" advice. An article on the web by Purdue University specialists also suggests to apply early (as early as March 1 for northern Indiana), as the application will still be effective all season.

Scotts fertilizer has a type with a preemergent (crabgrass) preventive ... HALTS I think they call it.

In the mid-Atlantic, they say apply while the forsythia is in bloom.

If you're overrun now, pay a kid in the neighborhood to pull it up manually. Apply the Scotts/HALTS next Spring.

Get chemical called Atrazine. The only downfall

with this pre-emergence weed controler is that

you will need to apply it in Feburary while the grass

is dormant. Otherwise it will kill your grass. After you

spray it, it will have a residual control on weeds and

will kill them. You can find it at a agriculture chemical

dealer and I think at Wal-mart or Home Depot.