Good morning, and thank you for your question. As it happens, this question was sent to another master gardener and her response is copied below. She provides a link to the Department of Entomology at Cornell and, after accessing that site, I found that Kyle Wickings is the entomologist who specializes in animal and insect impacts on turfgrass. Becky, the initial master gardener, asks questions that will help the Cornell expert in giving you the correct diagnosis. I hope this information helps you.
Jeanne


Hello!

At this size, the holes were most likely caused by an insect. Without additional information, it's difficult to say what insect it might be--perhaps ground nesting bees or wasps, or even ants (without mounding). Are you seeing any specific insect activity in the area? Do you know when the holes first appeared?

As a reference, the article as this link has photos of the entry points of ground bee nests: https://entomology.cals.cornell.edu/extension/wild-pollinators/native-bees-your-backyard.

I believe that the insect burrowing is a result of the thin turf, rather than the cause. The insects are taking advantage of the direct access to the soil.

Some additional information about the turf might help sort out the problem. Unfortunately, that means I'm going to ask a bunch of questions. When did you first notice the change in the turf? How much do you water this area? How often and how much fertilizer do you apply? Have you had the soil tested? If so, do you know the soil texture? Does the area drain well? How many hours of sun does it receive?

Regards,

Becky Irey Replied June 12, 2018, 12:57 PM EDT

Thank you so much for your reply. In response to some questions below, we have only lived here for two years. We have never treated the lawn. We have had significant amounts of rain this summer so no need to water. We have not noticed any significant bug or bee population but have noticed many birds in this area and have noticed at times hoards of birds, possibly a hundred or more, on the backyard lawn, apparently feeding on whatever is under the grass and possibly causing the holes. We have never applied fertilizer, there is no drainage problem and we get sun from late morning through the early evening. Wondering if we need an entomologist or a lawn specialist to try to solve this problem?

Hello again,
There's a lot of information to follow, so please be patient with me. I found quite a bit for you to read so that you can try to identify what's causing your grass to yellow and what's attracting those birds. I hope this additional information helps you to discover what's causing the problem in your yard and that you can remedy it without the use of chemicals. For information on lawn care, please go to: https://extension.psu.edu/lawn-management-through-theseasons#:~:text=In%20most%20cases%2C%20turfgrasses%20benefit,or%20late%20summer%2Fearly%20fall.
Jeanne

There are quite a few insects that birds will eat from turf. Among them are grubs that will be devoured by crows, starlings, grosbeaks, magpies, robins, and blue jays. Other insects include big caterpillars, beetles, other medium and large insects and spiders they find near the ground. Blackbirds, bluebirds, sparrows, crows, wrens, and other birds get a lot of protein by hunting out these insects.

If you have grubs (that chew on the roots of grass), you'll be able to rip up sections of lawn with ease. You wouldn't know, without digging, that you have them. 

For those choosing a more natural grub treatment as to how to get rid of lawn worms, there are several options available. All of which are considered safe and effective. These include milky spore, neem oil, and nematodes — available at most garden centers.

Once lawn grubs have been detected and treatment is necessary, you need to know when to apply grub worm treatment. The best time for treating grub worms is in late summer or early fall while the grub worms are still small and close to the surface.

Although caterpillars aren’t damaging in small numbers, when a caterpillar population grows excessively, they can become a significant issue for your lawn and other plantings. These caterpillars mainly feed on your grass. When they are young, they feed on the upper surface of the grass blades, leaving off-color spots. Adults will eat entire sections of leaves, causing large unsightly, brown spots. 

You can use the drench test to see if they are the culprit for the brown spots on your lawn. Combine dishwashing liquid and water and pour it over one square yard of your lawn. Count the number of caterpillars that surface. If you have more than fifteen per square yard, you likely have an infestation.

American robins, red-eyed vireos and Carolina wrens are very fond of caterpillars. Yellow warblers greedily consume larval lepidopterans, which make up about 60 percent of the warbler's diet.

Chinch bugs feed on the grass blades causing the grass to turn a yellowish color then a brown color and then it dies. Once the grass dies, the chinch bug moves on to the next blade. Because they feed on all types of grass, chinch bug damage tends to appear as patches of brown grass with healthy blades mixed in. 

Chinch bugs are born in May, so their destructive phase begins in early summer as they continue feeding, but you may not notice the damage until late summer. A full-grown Chinch body is less than ¼-inch long and has a dark red to black body, white wings, and a white dot on its back. Nymphs are easily recognized by their bright red color and white band across their abdomen. Both adults and nymphs produce a strong odor that often gives them away, especially when pest numbers are high or they are crushed underfoot.

You will typically find Chinch bugs on lawns at a rate of fewer than 10-15 bugs per square foot of lawn; however, it is vital that you do not underestimate these small bodies.
The right conditions (extreme heat and drought) can cause the population to multiply to over 100 bugs per square foot of lawn. Evidently, these bugs can do extreme damage to your lawn if left untreated. 

There are a few ways you can tell if your lawn has cinch bugs. The first way we recommend is by simply using a magnifying glass and your bare hands. 
Since these little bugs do no harm to humans, there is no need to worry about getting bit. You can find these pesky insects best by spreading the grass near the soil on the outer edges of your lawn and searching the thatch layer.

You may also examine the surface of the soil and the undersides of grass stolons, which are root systems that extend above the ground. The other way is to use a coffee can. Here’s what you’ll need to do:

1. Cut the bottom and top lids off a coffee can.
2. Push the can into the ground using a twisting motion.
3. Fill the can with water.
4. Wait for approximately 10 minutes.
5. See if any chinch bugs float to the surface.

Beneficial Insects Controlling Chinch bugs Include
Earwig, Ground Beetle, Rove Beetle, Assassin Beetle; Minute Pirate Bug, Ants, Spiders, and Parasitic Wasps. Quite often these beneficial insects are misidentified and are needlessly killed with insecticide.

A number of parasitic wasp species lay their own eggs inside the chinch bug's eggs. Ants and spiders devour their eggs too. Encourage these beneficial insects to reside in your yard by avoiding the use of broad-spectrum insecticides and planting lots of kinds of flowers to offer them nectar and pollen.

A healthy population of songbirds including your yard as part of their territory can go a long way to keeping chinchbugs under control. Songbirds that eat chinchbugs include: Bluebird, Cardinal, Catbird, Finch, Phoebe, Robin, Song Sparrow, Flicker, Woodpecker, and the Wren.

What can you do? For a moderate chinch bug infestation, vacuuming the lawn is the easiest solution and one of the most effective ones, too. First, rake the grass thoroughly starting 2 feet out from the edges of the affected area, working from the edges toward the center. Use a wet-vac to vacuum the entire area you raked, then water the lawn.

Another way to treat infestations in limited areas, spray down the affected areas using the hose end sprayer along with mildly soapy water, paying close attention to the border between the damaged grass and the healthy grass. Spread a white flannel sheet over the area and wait around 15 minutes. Pull the sheet back, and you should see the bugs attached to it. Remove them and put them in a bucket of soapy water.

To get a more wide-spread infestation under control, sprinkle a fine layer of diatomaceous earth over the lawn. This natural substance kills chinch bugs and other damaging insects, but won’t harm earthworms, plants, pets or people. Nature can help you clear up moderate infestations, too.

Thank you so much for this thorough and very helpful information!!

Sent from my iPhone



You're very welcome. We're here to help - 
Jeanne