Sounds like you are doing good work for your EX! lol!

To me that sounds about right, the speedzone, or most broadleaf herbicides, are contact kill only and have almost no soil residual. Since the seed you put down was... seed, there was no part of it to absorb the chemical, no foilage, no root yet. By the time it did germinate the speedzone was long gone on the soil surface and had done it's job translocating thru the actively growing plants that were there

 

Just FYI

I applied a blanket app of Speedzone at 1.5 fl ozs. per K to a 2000 sq. ft. area of my ex's lawn and slice seeded it 1 hour later with turf type tall fescue. Had germination in 6 days. This was 3 weeks ago and new grass is ready for first cut. How about that?

David

A little risky but I'm glad to hear it worked. I am guessing that by slit seeding you had enough seed down a 1/2 inch or more in the soil that the herbicide didn't affect it, but seed higher in the soil profile probably didn't fare as well. Thanks for the post, I will be a little more daring in the future.

 

Most selective broadleaf herbicides do have a residual, I believe. Speedzone is an ester formulation (of systemic herbicides and a small amount of carfentrazone-ethyl, a contact herb..) and the label says to wait a week before seeding. Most amine formulations recommend waiting 3 to 4 weeks such a Trimec, Three-way, Momentum, etc.

However, as long as the herbicides aren't contacting the soil in excessive amounts you could realistically seed as soon as the the chemical dryed, if the weed canopy is thick enough.

I have spot-sprayed broadleafs in yards with Momentum using a backpack with a fan tip, core aerated (lawn dry by the time I finished), and spread seed with great results.