Thanks for the question.

What you observed with your turf is a classic symptom of Japanese Beetle grub activity. See:

https://www.mda.state.mn.us/plants-insects/japanese-beetle

https://extension.umn.edu/yard-and-garden-insects/japanese-beetles

http://www.minnesotaseasons.com/Insects/Japanese_beetle.html

The grubs that caused this turf damage came from eggs in the soil that had been deposited in June 2022 by adult beetles. During late July and early August of 2022 these eggs hatched into small grubs that began to destroy the roots of your grass.  This caused the grass to die and be easily pulled up. 

You indicated that your lawn received grub control treatments. When, precisely, did these treatments occur? If they were done in May and/or June of 2022, these treatments would have been relatively ineffective. The grubs (from eggs laid in 2021) that existed in your turf at that time were too large to be affected by any chemical grub pesticide.  It would have been a waste of both time and money. Effective grub control treatments have to be performed when grubs are in a very small stage.  Additionally, some grub control procedures are relatively ineffective even if done at that time. Other procedures can be effective. See:

https://thegoodearthgarden.com/japanese-beetle-control/ - :~:text=For Japanese Beetle grub control,as any signs are evident.

https://biologicco.com/blog/why-late-summerearly-fall-is-the-best-time-to-treat-for-white-grubs/

In short:

1). The turf damage in 2022 was done by grubs that hatched from eggs laid in late June 2022 by adult beetles;

2). The effective treatment window for preventing this damage would have been late July to early August 2022. Spring 2022 treatment would have been largely ineffective as small grubs would not have been present.

3). Most likely there are now Japanese beetle grubs in your soil. There is no treatment for them at this time nor will there be any effective treatment for them in early 2023.

4). The existing grubs in your yard will develop into adults in June 2023. These adults will mate and deposit eggs.

5). Do grub control in late-July, early-August 2023 to minimize 2023 turf damage.

6). Ask your lawn service exactly what type of control measures they did in 2022, when they were done, and precisely what types of chemicals were employed. Compare these chemicals with the effective chemicals listed in one or more of the above suggested sites.

Good luck and please get back to us with any additional questions.

As you can see from the scanned service tickets, Davey treated for grubs on 6/24/22 and 8/17/22.  I don't know which of the three products applied is for grub control.  So, to clarify, the insect control product (nematodes, for example) is only effective when the larvae are very small?  Is there any point in re-seeding the lawn in the spring if there are larvae in the ground now that will hatch?  My concern now is when to re-establish the turf and how to prevent it from being damaged again.

Thank you in advance for clarification.

Thanks for the reports from Davey. 

The treatments on 6/24/22 and 8/17/22 were identical with respect to what was applied. In both instances a liquid fertilizer was applied that consisted of 12% nitrogen, 0% phosphate, and 6% potassium. This is shown under “Fertilizer Applied”. Bandit 2F is an insecticide that kills a variety of insects including Japanese Beetles. However as I looked further into this insecticide it seems to be effective only against adult beetles and not grubs. The Quin-Way 75 DF is a general herbicide intended for weed control. Three-Way is also a herbicide for weed control. In short, there did not seem to be anything in these two applications that would deal with Japanese Beetle grubs. Although you mentioned nematodes in your response, and these would have an impact upon grubs, there does not seem to be any inclusion of nematodes in either of these two applications. Perhaps you had nematodes applied to your yard by some other vendor? Or maybe you were just mentioning nematodes but not implying that they had been applied to your yard?

Will look forward to your response for further clarification. Many thanks for your time.

I have again looked over your treatment sheets.  I see that "grub control" WAS checked on both sheets.  I inadvertently missed this during my initial review.  Unfortunately it did not specify the nature of this control.  This is an important piece of information in order to determine how effective this treatment might have been.  Will continue to research this..  Thanks for your patience.

In further looking at your treatment sheets, we believe that the 6/24/22 grub treatment may have been relatively ineffective. At that time most of the grubs previously existing in the soil had either entered into a pupal stage and/or already matured into adults. The 8/17/22 grub treatment was done at an appropriate time period. However without knowing exactly what comprised this grub treatment, it is difficult to assess its effectiveness. Whatever was done did not appear adequate to control the grubs given what you subsequently observed with your turf.

With respect to future grass seedings, it would appear likely that in spring 2023 there will be grubs present in your yard. They will be at a large stage and relatively resistant to chemical grub control. These large grubs should not do significant damage to your turf at that point and we would encourage you to do some reseeding in the spring. Then pursue some type of chemical grub treatment in early to mid-July. See the following:

http://cues.cfans.umn.edu/old/extpubs/7664japanese/DG7664.html - :~:text=Preventative chemicals should be applied,they pupate (Figure 3).

Please get back to us if you have any further questions. Good Luck!!