Preemergent Herbicide Facts Questions from Our Visitors

Paul Asked: I have a question about preemergent herbicide. I recently overseeded my tall fescue lawn. However, I used Scott's Turf Builder with Halts preemergent by mistake. Now my seeds will not germinate. Is there an immediate rescue or am I out of luck for 4 months?

North Carolina
(See Answer Below)

Answer: Hi Paul. I am unaware of any easy method of neutralizing a preemergent after it has been applied. The preemergent forms a barrier over the surface and is not easily removed. However, there is one possibility. Some have suggested applying "activated charcoal", but I have personally never tried it.

You can purchase activated charcoal for lawn use. One web company is

I haven't used a lot of Scotts homeowner products, but while the fertilizer seems okay, I am not impressed by some of their other products they include with it.

For example, my mom has 1/4 St. Augustine grass and 3/4 of her lawn is Turf Type Tall Fescue in the most shaded areas. She applied a Scotts fertilizer that was labeled "For St. Augustine Grass Only" and says it has a herbicide that will kill fescue and other cool season grasses. Apparently she didn't read the bag close enough and she applied it over all her grass, including the fescue. It had no effect at all, no yellowing, nothing on the fescue. Maybe you will have some luck and your grass will grow.

If not that then I suppose you will have to wait until next year. I'm sorry I don't have a better solution for you. Let me know how it works if you try it.

Second Preemergent herbicide Question

Carol Asked: I may have waited a little too long to apply a preemergent to stop crabgrass from growing. I am not certain if any seeds have germinated or not though. Is there any type of preemergent herbicide that will stop seeds from germinating and also kill crabgrass that is already growing?

Carol C.
Norman, Oklahoma

Answer: Hello Carol. Yes, there is a product that will kill crabgrass in the seedling stage and continue to prevent other seeds from germinating. The Product is called Dimension 2EW Dithiopyr Pre-Emergent Herbicide. Click here if you want more information: Dimension Herbicide

This particular preemergent product is a liquid and is mixed with water and then sprayed on the lawn through a garden sprayer, backpack sprayer or larger sprayer if you have one. Be sure you cover all of the lawn, not just the trouble spots for the best results.

You can also get a granulated fertilizer with Dimension preemergent herbicide already added to it if you haven't fertilized yet. You can kill two birds with one stone this way.

Once the crabgrass has grown beyond the seedling stage, Dimension becomes less effective, but will still be effective on weed seeds. Dimension is one of the products professionals use. It is longer lasting than many other brands.

Remember, don't reseed your lawn this spring if you plan to apply a preemergent now. The preemergent herbicide can't tell the difference between the crabgrass seeds and your lawn seed.

Third Question Concerning Preemergent Herbicides

Randy asked: Hello Mr. James. You mentioned that Dimension and Barricade preemergent herbicides will last the whole season. Are the others as good, such as Scott's Halt? Will they work on broadleaf weeds, as well, like dandelions?

Randy Hollister
South Carolina

Answer: Hello Randy. Great questions! First the dandelion question. Dandelions must be controlled with post-emergent broadleaf herbicides, such as Weed-B-Gone, etc.

If you pull them make sure you get all of the root or as much of the roots as possible. If you cut the root in three pieces and plant them it will grow three more dandelions. The root must be removed.

Dandelions are perennials and will go dormant in warm weather, but are very much alive. As far as I know, most preemergents have little effect on the dandelion seed heads. I wish it did.

"Dimension" and "Barricade" are professional preemergents often used by commercial landscapers and turf professionals. I used them as well. Here is a link to check out how the two preemergents work: Barricade Preemergent and Dimension Herbicide.

They are also available to homeowners and will last the whole season. Halt brand may give 5 months of protection at best. If you apply it in Feb., it may stop working in mid summer. You may get some crabgrass that comes through, especially if you had widespread crabgrass before. However, it will probably not be nearly as bad as if you had applied nothing.

Dimension and Barricade work extremely well on crabgrass and foxtails and several other grassy weeds. However, I have found that they don't work nearly as well on broadleaf weed seeds, even though they list them as ones they control. Try "Gallery" preemergent or Preen if you are looking to stop broadleaf weeds from growing from seed. These are much better for broadleaf seeds than many other preemergents.

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