Asked May 31, 2022, 3:12 PM EDT
Hello, we would appreciate any feedback or advice on diagnosis and treatment for the below situation.
Summary:
Despite practicing proper turf management to the best our our abilities, we are actively experiencing die off of KBG turf. We previously identified 2 potential root causes, an over application of pre-emergent last fall and/or a fungal issue. Last week, however, we found what we believe to be European Crane Fly larvae in the impacted areas, and are wondering if this could be our true root cause.
Background:
We built our house in 2018. In October of 2018, we had approximately 12,000 sq ft of KBG blend sod installed (your typical SE Michigan sod farm blend). Throughout 2019 and 2020, we had no issues with our turf. During these years, I strived to learn and adapt proper turf management practices...watering 1/2 inch every 3-4 days, mowing twice a week at a height of 4 inches, having our soil tested, etc. During these years I fertilized exclusively with Milorganite approximately 4-5 times a year, including a "winterizer" application. We strive to live organically, and no pesticides have ever been applied to our turf. By most measures, our turf was thriving...and neighbors often commented on the health and appearance of our lawn.
In the winter of 2020/2021, our turf appeared green, thick, and healthy. However, as temperatures started to warm throughout March - June of 2021, I noticed a slight yellowing/die back of approximately 500 sq ft of turf in our front yard (facing north east). I struggled to diagnose this, and outside of sharping my lawn mower blades to eliminate this as a source of yellowing, did nothing to correct the problem. By fall of 2021 this section of turf had completely recovered. Also, in the spring/summer of 2021, I became concerned regarding the phosphorus content of Milorganite (soil test showed phosphorus at the top of the recommended range), and switched to a 24-0-6 fertilizer in Spring/Fall, and a 7-0-20 fertilizer in summer.
In November of 2021, I applied 7-0-20 fertilizer as a winterizer. I also applied Prodiamine as a preemergent in October of 2021. Nothing else was applied to the lawn. As winter went on throughout January/February of this year, I noticed a significant browning/yellowing of our turf. It presented itself as almost like an extreme dormancy, and was much more sever than what we experienced in 2021. By late February/early March of this year, our turf was the brownest on our street. This surprised me, as our lawn typically stayed green thought the winter. I thought perhaps this was due to the cold temperatures and lack of snow cover. Indeed, the areas that appeared the most brown were exposed to significant wind, thus blowing away what little snow we had this past winter and exposing the turf. I also considered perhaps I over applied the Dithiopyr (I likely did, as I accidentally applied enough Dithiopyr for 17,000 sq ft to an areas of only 12,000 sq ft), and killed off part of the turf.
As surrounding lawns came out of dormancy in late March/April, it appeared as if ours never did. In fact, just the opposite. As temperatures warmed, our turf got worse. I fertilized an application of 24-0-20 in late April, but this had no impact on the browning areas. I also applied a Spring application of Prodiamine at the recommended rate. The hardest hit area was the 500 sq feet in the front yard where yellowing had also occurred in 2021. But this spring the browning/die off had also spread to rear yard (impacting approximately 2,000 of 8,000 sq ft), and the side yard. Interestingly, the side yard facing south has no damage. The impacted areas are often where our turf was the healthiest and thickest. I raked the impacted areas, thinking perhaps we were hit hard with snow mold. Raking didn't make a difference, as the impacted turf was already dead. With every mow from April through May, the turf appeared worse. Noticing that the die off was spreading with each cut, I applied Scotts Disease Ex in early May. The Disease Ex doesn't not appear to have stopped the problem from spreading. I have also purchased liquid anti-fungal for a second treatment, but have not applied it due to finding the European Crane Fly larvae.
This past weekend, I dug into multiple spots in the turf (near the dead areas) and found no evidence of grubs, sod webworms, etc). We also do not have a dog, and our neighbor's dog does not pee on our lawn. I did however notice that the turf in the dead and near-dead areas had roots only extending 1 -2 inches into the ground, versus 4-5 inch roots in previous years. The brown grass does not pull out easily, such as I would expect from grubs. In addition, the grass shoots appear healthy, until they suddenly turn completely brown in a patchy pattern.
Last Friday I was digging in the turf around my wife's raised garden bed to lay pavers, and found this green worm/grub consistently throughout the area I was digging...perhaps one green grub for every 2-3 inches of soil. There was no damage to the surrounding turf...just the worms in the soil. My wife googled the image of the grub, and determined it was potentially a European Crane Fly larvae. Neither of us had ever heard of this insect, although we do experience the adults during summer. I went back to the browning areas of turf in the front yard, and found the same green grub there, perhaps one worm every six inches or so. Maybe there are more of them than I have found...I can keep digging and report back.
Opon further googling, it seems that European Crane Fly larvae should be present in larger numbers than what I found to experience the type of die off we have. Could this be the cause of the damage? Could I have killed off the lawn with an overapplication of preemergent?
I would like to stop whatever is happening, as the die off of turf seems significant enough (and rapidly increasing) that it doesn't seem likely that it will just going to grow back on its own throughout the season. I also doesn't want to have the same problem next spring We have researched Nematodes as an organic solution, but Google suggests they only have a 50% chance of success.
We are ok with a chemical/pesticide treatment plan if necessary to stop the damage from spreading throughout the rest of June, but will not consider using a chemical that is moderately or highly toxic to birds (my wife has many feeders and has given first names to all of the birds that frequently our yard). Carbaryl seems like a remedy that would stop the European Crane Fly larvae instantly with minimal impact to birds, but it is expensive and hard to come by, and I don't want to apply chemicals without reasonable certainty that I need to. We are not adjacent to any waterways, so we are less concerned with the likelihood of any potential impact to aquatic life or water (at least as opposed to impacting birds). We also have a larger than normal amount of birds picking through our lawn, perhaps for earthworms, perhaps for larvae, I don't know.
I have more pictures available if those would be helpful. Thanks again!
Washtenaw County Michigan
