Thanks for the question.  I will be glad to help you. But first two questions for you. How do you know sod webworms are the specific cause of your lawn issues? Secondly, have you actually seen any larvae on the grass?  If so, try and take a picture of them and send to us. 

Many thanks. We appreciate you consulting with us. 

Thanks for getting back to me. Yes, timing is critical in controlling them.  The larvae are susceptible to treatment at only a certain temperature. Can you tell me what the current temperature is in the underlying layer of thatch?  By the time you see adult morhs, it’s too late. Please describe what types of treatments you have done. If insecticides were applied, do you know their specific names?  I ask this question because it has been shown that certain insecticides are ineffective against them. 
Will look forward to your response so that we can develop an effective treatment strategy.  Thanks

Thank you for that information.  I am consulting with a colleague from the U’s Entomology Department regarding your webworm situation.  I anticipate having a complete analysis for you by Monday (5/6/24).  For what’s it worth, these are the insecticides that the U recommends for treatment against webworm larvae:

Thanks again for your patience. 

Good day .  Just a brief update after talking to my entomology colleague. Imidacloprid 2f seems to be inefficient against webworms. Will provide documentation on 5/6. Unfortunately it is very lethal against most sucking insects. This would include friendly pollinating insects. Not something that is very environmentally friendly. How many years have you been using it?  If for several years, this would explain why you have been unsuccessful in getting rid of webworms. The challenge continues.

With your assistance, we will resolve things. Thanks. 

Thanks again for your patience. I have been inundated with over 30 thirty questions since Sunday (5/5/24) and have been attempting to do my due diligence to them all. Yours included.

My Entomologist colleague first suggested to me that you should be apprised about the life cycle of sod webworms. Although to a point of pain you may already be aware of this, the following site will get us started:

https://entomology.unl.edu/turfent/documnts/swebwrms.shtml - :~:text=Life History,-May to mid-June.

There are a few take away lessons here:

1). Only the larvae (caterpillars) are susceptible to insecticides. I suspect that you already knew this. The larvae that will soon be hatching (late May, early June) originate from eggs that were laid last fall and are now hatching. These hatched larvae will make their presence known by the appearance of white moths. You are probably familiar with this. These adult moths will quickly mate and lay eggs. These eggs will result in larvae appearing in late July and early August.

2). You have two windows in which to intervene in this process: NOW and then in July. But please keep in in mind that you will be dealing with two moving targets. A single intercession, perhaps what you have done in the past, will not suffice. New larvae will constantly be emerging over a period of time in both windows. I suspect that in the past only one application of insecticide was done. If so, I’m not surprised that it proved ineffective. This not a one-time event.

3). Be prepared. You may not be completely rid of this pest. Moths from adjoining properties may fly into your property and lay eggs. In other words, despite your best efforts in 2024 be prepared for the presence of sod webworms in 2025. There is nothing you can do to prevent this.

My suggestions based upon information given to me from my colleague:

1). In the areas of your grass that may now be turning brown, rake it extensively, gather debris up, and discard in the trash.

2). Apply an insecticide that contains one or more of the ingredients mentioned in the following:

https://extension.umn.edu/yard-and-garden-insects/sod-webworms

3). Apply this insecticide ASAP.  Follow the application instructions on the label. Then wait a couple of weeks (maybe until early June 2024?) and make a second application of insecticide.

4). Keep watching for the appearance of any moths. If any appear, that would be a signal to do another application of insecticide. Even in the absence of moths, a second insecticide treatment in mid-July would be a good precautionary step.

I apologize for not getting this to you sooner. Good luck and please get back to us with any questions.

Thanks for your question.

There is really no difference between using granules or liquid insecticide. Also from an environmental perspective, it doesn’t make much difference. What might be different is the application wording that might appear on the product label. Read it carefully. You should also be consistent in only using liquid or only using granules. Do not mix the two together.

Again thank you for consulting with us.

Glad to have been of assistance.

Please keep us informed as to the progress of things.  Best of luck and good wishes.