Crabgrass: Two Professionals Disagree

[Jed1]

This is in SE Wisconsin. Newer seeded lawn (Kentucky Bluegrass, Tall & Fine Fescue, Rye) w/irrigation system. Sandy soil. A lot of crabgrass.

One local lawn care company wants to spray a post-emergent control now, then return and slit-seed by the end of September, then use pre-emergent in the spring (in addition to fertilizer & broad leaf treatments). Their theory for slit-seeding is that the die-off of crabgrass will be so significant that the bare areas will be noticeable and will facilitate soil heating in the spring, thus breaking down the pre-emergent barrier. This will be an expensive option.

The company that installed the lawn disagrees, and says to fertilize and treat the broad leaf weeds now, then use a pre-emergent next spring. They believe that fertilizing and good mower height will encourage the turf to spread and crowd out the crabgrass.

These are both reputable firms. Any suggestions?

[mngrassguy]

They are both right. Option "A" will produce a greener, healthier lawn faster. Option "B" will cost less but take a much, much longer time to get there. Expect cg to get better each year but you will battle with it for awhile.

[heybruck34]

Fescue won't crowd out the crabgrass- just the opposite. That being said- the thicker grass you have, the less crabgrass will germinate from seed.

Pre-emergent is the key for crabgrass- I would go with option A- a 2 pronged attack is always best. CG is a very tough weed to control.

[Grandview]

I am just north of you so I have a little insight. I would not do any post emergent now. Crabgrass quit growing three weeks ago. The overseeding question is tougher to answer without seeing the lawn. There is no harm in waiting to see if over seeding is needed. I would fertilize at least twice this fall and mow at 3 inches or higher. Broadleaf weed control should also be done if the lawn has been mowed at least three times. You can put the lawn on a good fertility program for a year and see what happens. I have walked away from lots of overseeding jobs by telling customers lets try a good fertility program for a year. After the year 90% of the time over seeding is no needed. Bluegrass can fill in some big areas.

[AI Inc]

I would ignore the crabgrass for this yr as it will be dieing off. Overseed with just seed and starter fert. Pre emergent next spring. Thinking long term you will always have crabbgrass probs untill that sand situation is taken care of.

[Marcos]

I would ignore the crabgrass for this yr as it will be dieing off. Overseed with just seed and starter fert. Pre emergent next spring. Thinking long term you will always have crabbgrass probs untill that sand situation is taken care of.

I ditto Al Inc's input.

Grassy annuals certainly will be on their way out (turning purple) in your area within maybe a week or two.

I would have it aerated 1st very thoroughly, THEN have it slice-seeded starting an hour or so later (minimum).
What this does...is allow the slice-seeder's blades to 'chop into' the deposited soil cores that were left all over your lawn by the aerator, thus increasing the % of seed-to-soil contact during the operation significantly!
Make sure that you mow your lawn relatively 'close' before they do this!
It will help them see what they're doing much better, and relieve stress on the equipment. But most importantly, it will help keep your EXISTING turf from later 'competing' your newly germinated seed 'to death'. :waving:

[Jed1]

Thanks to all the professionals for their advice on this. There were different views, but I'll go with the pre-emergent route next year and talk to the original contractor about over-seeding now, and see what he thinks. He has a good handle on this situation, and has done well so far. Anyway, I pushed one of those slit seeders around at my previous house, and no way am I doing THAT again! :)