Hello David,

I checked a random granular lawn herbicide with a popular brand name. The active ingredients are 2,4-D, Mecoprop-p and Dicamba. The manufacturer states that you should wait three weeks after application before planting seed. Sorry, but we cannot recommend any specific product. A quick journey through your favorite big box store or nursery will afford you dry granular fertilizers that will work. Just read and study the instructions including the safe to seed time.

Since the herbicides will be effective whenever the weeds are green and actively growing you can apply herbicides until late fall. You should generally wait for 6-8 weeks after seeding before you apply herbicide. So, if you seed right now, it would be safe to apply herbicide mid to late October. Some years we might still have weeds green and growing at that time.

Alternately, if you apply the herbicide now, you can seed early to mid September which puts you in the perfect time to grow grass sed in the fall in Michigan. This is your best option.

Here is an MSU article on fall lawn seeding: https://www.canr.msu.edu/news/six_steps_to_fall_turfgrass_establishment

Hope this helps.

Many thanks for your reply!

On second thought, it appears from the photo that I'm dealing with annual weeds(?) that should be killed by the first frost(?). If that is, in fact, the case, should I wait until early September to mow low and bag the clippings, followed by overseeding? Forget the weed treatment altogether?

Thanks again,

Dave

Hello Dave,

You are correct. That is crabgrass and it is a summer annual. Once it goes to seed it will die back and you can overseed in mid-September.

There are herbicides that are effective as post-emergent crabgrass control (mesotrione, quinclorac), but they may have waiting periods after application before you can safely seed. You would need to research crabgrass post emergent control and choose your overseeding mixture to determine any necessary waiting time based on the grass varieties in the mixture.

Do you normally apply crabgrass pre-emergent herbicide? It is very effective at controlling outbreaks like you are experiencing. Products that can be obtained at your garden center or big box store are usually crabgrass pre-emergent herbicide mixed with spring fertilizer. They are highly effective when applied at the correct time. I usually watch forsythia bloom (the yellow spring shrubs) as a good indication that it is time to apply. However, there is a much more scientific method. Go to the MSU Growing Degree Days Tracker (https://gddtracker.msu.edu/) , enter your zip code and click on Crabgrass PRE in the right panel. This will show you color bands of when the appropriate time to apply the herbicide product is in your area.

Good luck with your project and hope this helps.

Again, thank you so much!

I believe you answered the question that follows, so excuse my need for confirmation. Based on my situation, would I be better served by not bothering to address the annual weeds at this stage? Given that they are going die back, the concern about competition with the new seedlings for resources seems to be less of an issue.

To answer your question, I was a regular user of the crabgrass preemergent but couldn't this year because I overseeded in the spring. I certainly will going forward. 

Again, I can't thank you enough for your assistance. This service is wonderful.

Take care,

Dave

Hello Dave,

For future reference, there are pre-emergent products that are safe for seeding grass and preventing crabgrass germination.  They contain mesotrione.  You can find them at your local garden center.

My only concern is the coverage of the crabgrass at the optimal time to seed.  Its prostrate habit covers a lot of the soil.  But the crabgrass should be declining when you seed and it will not compete with the seedlings.  I would be careful to get good seed to soil contact.

Best of luck.