"I read the instructions and it says not to seed for 4 weeks after applying. "

"Do you think I can apply this stuff and safely do an overseed in a week or 2?"

No.

"If there is a pre-emergent in it, will the core aeration nullify this effect and allow me to successfully overseed?"

No. This isn't interfering with germination by blocking the seeds from getting established. It's killing the new grass that isn't established well enough to withstand the weed killers. Don't apply it after the seed germinates, either, until you've mowed the new grass at least three times (preferably four times).

Thanks, bp! I didn't realize this stuff stayed in the ground for so long I guess. Figured a couple weeks with some rain would take care of it. Do you know which of the active ingredients are the pre-emergent? I guess I could spot RU some of the areas instead.

"which of the active ingredients are the pre-emergent?"

None of them, that is a post-emergent spray for weeds that have already sprouted and actively growing. You are right, I would go ahead and spot RU some of the areas.

"None of them, that is a post-emergent spray for weeds that have already sprouted and actively growing."

Thanks! Wow, that seems counter-intuitive...I can seed after applying a product that kills everything but not after a product that kills weeds. I guess I'll return the product or just save it for later use. Thanks again.

Sulfentrazone is a preemergent herbicide. Interesting that the label doesn't make that clear.

Here is a link that might be useful: label

Yeah, some labels clearly show the product as a pre-emergent. Is there any OTC weed killer I can use and still seed in a couple weeks? Thanks!

"Is there any OTC weed killer I can use and still seed in a couple weeks?"

If you want to kill everything, you can use glyphosate (Roundup is the best know brand name). I've heard of people planting within days (I think one person seeded within hours) of using that.

I'd rather not kill everything...there is some decent grass under this unknown weed.

You're right jayk, I guess I overlooked the Sulfentrazone ingredient (oops, my bad).

seven333, do you know if the weeds are broad/narrow leaf, annual/perennial? I assume they are some type of narrow leaf, since you got the crabgrass killer. Either way, selective OTC post emergent lawn weed killer labels say to wait 3-4 weeks to seed after application, or to wait until the 3rd-4th mowing to use weed killers on newly seeded lawns. I really don't blame you for not wanting to kill everything, especially if the weeds can be controlled with pre/post emergents.

firstandgoal...I'm really not sure what the weed in question is. It's lighter green than the rest of the lawn and grows faster. I posted a picture on another site but don't know if I'm allowed to link that thread here. Part of me thinks it's Poa Annua, another part thinks it's crabgrass but it's still growing upright. Don't think the weed killer would take care of it if it was annua anyway.

So in reading these comments it appears that it's safe to overseed your lawn in the spring at least 4 weeks after it has been applied? Correct?

Who knows? The comments were made 7 years ago. They may have changed the active ingredient 3 times since. Best to read the label on the bottle.