Spongy sections in yard with shallow roots

Asked October 21, 2018, 6:36 PM EDT

I have a few small areas of our north facing yard that feel a little “spongy.” In looking at these sections up close and digging in with my fingers into these spots, the grass roots are extremely shallow...almost a void between the grass and the soil...thus why it feels a little spongy when you walk on them. When first looking at the yard, it doesn’t look obvious. I only noticed it when the grass above it died and then turned brown. It’s odd as the grass doesn’t turn brown in this condition...until it dies due to the void underneath and extremely shallow roots. One lawn company said we have Ascochyta Leaf Blight, but didn’t think that killed grass...was more aesthetic. Another said they thought it was a digging animal, but that result in obvious holes. It doesn’t appear anything is digging under it, and I didn’t see anything like grubs. Just curious if an expert had recommendations?

Arapahoe County Colorado

2 Responses

It's a bit unclear what is happening in your lawn. First, ascochyta leaf blight doesn't occur this time of the year. By a "void" between the grass and the soil, do you mean that the dead grass pulled up easily from the soil - that you could peel the grass up from the surface? It's quite possible that you had an insect called the cranberry girdler (aka the subterranean sod webworm) feeding on the roots of your grass - which will kill the grass and allow it to be easily pulled up from the underlying soil.
These insects are quite difficult to control at this point in their life cycle. You will likely have to reseed or resod the affected area next spring.
It is unlikely that these insects will reappear next year. Their occurrence is sporadic in both time, as well as in where they occur. It's possible that you will never see them again in your lawn. Read more here:

http://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1888&context=extension_curall

Thanks for your reply. For clarification on the void...initially, the grass appears to be fine, but when it is starting to turn brown and die, I can stick my finger into the grass and poke under it...where there seems to be a "void" under this space.

In the past when I have had dead grass...it was simply dead grass with a firm topsoil. In this case, there is a small void under the grass that initially seems to be ok, until it finally dies...I assume since the grass roots are not in firm contact with the soil underneath. When I walk on these particular spaces, it feels "spongy" underneath.

I haven't seen any evidence of the insects noted above, but can check again.

I am going to attempt to try and take a picture later this week to help illustrate. It seems that I almost need to dig a small 12" x 12" section to better illustrate a cross section of the turf.