How to use pre-emergent and overseed in Fall

Asked August 2, 2019, 4:33 PM EDT

I live in Commerce City and I have Kentucky Bluegrass on my lawn.
I want to overseed and add a pre-emergent herbicide in the Fall.
But, I am unsure about when to do each and how. Do you have any suggestions?

I heard that Prodiamine 65 WDG is good to use. But, I am open to other options.

Adams County Colorado

3 Responses

Sorry for the extremely slow response to this. I believe you already talked to one of our master gardeners about this issue. However, the short answer is the when and how will depend on the product and the weed you are trying to control. In terms of "when" the biggest consideration is that you get the product down before the weeds you are trying to control germinate. For most of the annual weeds that you would normally be trying to control in a lawn setting this means late winter or early spring. There are some cool season weeds which germinate in the fall but most of these are not huge issues in lawns. You also need to make sure that you don't put the product down so early that it breaks down or otherwise becomes ineffective. The label of the specific product you are using should give you information regarding how long it provides effective control.

"How" these products are applied depends on their formulation. Normally, they will either be in a granular form you use a spreader to apply or a liquid form applied through a sprayer or hose-end system. You can often times find the same chemical in different formulations.

Prodiamine is a fairly common preemergent herbicide which is often used to control weedy annual grasses and broadleaf’s. You should get good control most of the season if you apply it late march to early April. Read all instructions on the label of any pesticide you apply and be sure to follow them including wearing all prescribed protective equipment.

Thanks for the reply. I already planted seeds now and the instructions say 60 days after planting I can apply Prodiamine so I will apply in October when the ground temp is at 55 degrees.

For the fall you say apply in late March or early April. When would you overseed Kentucky Blugrass for the Spring. I'm thinking January or February. What are your thoughts?

If you are going to make a spring application of a preemergent you will likely not be overseeding that spring. Even if you put out the seed early as you suggested the seeds won't germinate till the soil temperatures warm up. You would need to watch for them to actually germinate then apply the product 60 day later. By then you will likely have missed your window for cool season weed control.