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Risk of using herbicide before laying sod?

Posted by tskm 9 (My Page) on
Sun, May 20, 07 at 15:30

I once laid a sod lawn and was soon plagued with grass weeds coming up through it. I swore I would do things differently the "next time". The next time has now arrived.

I recently killed with Round UP herbicide a bermuda grass invested lawn. I now plan to rotor till the native soil and add in some gypsum and compost, grade it and roll it. But before I lay the new sod (90% tall fescue and 10% Kentucky bluegrass)I wanted to thoroughly pre-irrigate the soil to activate the weed seeds and rhizomes near the soil's surface. Once they do, I plan to zap them with Round Up.

My concern is will the Round up residual in the dead new growth of weeds hurt the new sod that I plan to lay. I am being told different things?

How about if I use a pre-emergent herbicide instead? But will that kill the new growth of weeds from rhizomes? And most importantly will it harm the new sod?

My situation does not sound unique to me. Often people lay sod on soil that is not weed seed/rhizome free. What is the common practice when doing this?

I am not seeking well intentioned speculation as to the best course to take. Rather I hope to hear from knowledgeable people that have encountered my type of situation before and speak from personal esperience.

Thank you all very much.

Follow-Up Postings:

RE: Risk of using herbicide before laying sod?

Don't roll it. Rolling will tightly knit the surface, making the sod roots difficult to penetrate. You want the soil friable, not compacted.

Spread your compost and mix it in during the grading with a rake. That's good enough. If you till, there are thousands of weed seeds you could be bringing to the surface but never get them to germinate on this attempt. Plus, there are other disadvantages to tilling.

I don't exactly know what you mean by "thoroughly pre-irrigate" but make it about a week of shallow watering maybe twice a day. That's what weeds like, not saturation.

Roundup is not persistent in the soil. You can lay your sod one week after spraying the weeds. The herbicide will get into the growth of any plant it touches, not anything the chemical does not touch.

I don't know of a pre-m herbicide that controls germination of any weeds likely to grow this time of year. Pre-m only prevents weed seeds from germinating. Depending on which pre-m herbicide used, some will impede growth in early stages - shortly after germination. Just best not use it in this instance.

Just food for thought, you risk of alienating and never benefiting from some very knowledgeable people when you exclude them like that. Think about also, there may be someone who has done it before but doesn't mean it's the right thing to do.

RE: Risk of using herbicide before laying sod?

Beware of the pre-emergent chemicals. Some prevent root development and are unable to distinguish the roots of your sod from the rest. If you can get (almost) everything germinated and growing and you can wait until everything is at the 3-leaf stage (14-21 days), then you will have made the timing right for an application of glyphosate (2oz. of the 40% concentrate per gallon of water). Please wait for another 7-10 days to allow the chemical to get translocated to all parts of the plants and then lay the sod. And if you think that I sound like I've done that, you would be right; 30 acres of it.

RE: Risk of using herbicide before laying sod?

If you had a lot of bermuda, I would error on the side of caution. It is a very persistent weed and often requires multiple treatments of roundup. The general plan I would suggest would be - roundup everything. Wait 1 week. Use a string trimmer to cut off all the dead topgrowth and then rake it up. Water everything well to see what regrows. Wait 2 weeks. Roundup anything green. Wait 1 week. Use a string trimmer to cut off all the dead topgrowth and then rake it up. Then lay the sod.

If you just had some easy to kill weeds, you can usually get away with just killing them off, clearing the soil and then immediately sodding. Sod is thick enough that the seeds underneath will generally be unable to germinate.

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