Turfgrass Mystery: what happened to this green?


This is a MiniVerde ultradwarf bermudagrass green in the western part of Japan.

These photos were taken on 1 and 2 October. For a closer look at the grass, click on the image below:


At this location, the average air temperature for the previous three months had been 27.7°C in July, 30.3°C in August, and 26.3°C in September. Those are almost optimal temperatures for the growth of ultradwarf bermudagrass. It rained a lot in July, 454 mm, and then August and September saw 70 and 139 mm of rain, respectively.

In the worst area of the green, it looked like this:


However, it would seem that the weather in the preceding three months had been almost ideal for the growth of ultradwarf bermudagrass. 

The mystery is, what happened to make the green look like this? 

Here is one more photo. In the foreground is the mysterious MiniVerde green. In the background is a manilagrass (Zoysia matrella, called korai in Japan) green, that seems to be fine by comparison.

This was a tough mystery to solve, with many guesses, ranging from disease, to localized dry spot, to salt damage, to scald from hot topdressing sand, and many more. This damage was actually caused by application of the fungicide tebuconazole. I don’t usually expect to see fungicides having this effect on grass, so I found this a difficult mystery to solve myself. Here is the correct answer.

Thanks to everyone who helped to solve this. I have seen damage, sometimes severe, on ultradwarf bermudagrass greens in multiple countries in Asia after they have been sprayed with DMI fungicides (such as propiconazole or tebuconazole) at the label rate. Difenoconazole is supposed to be safer. For more information about DMI fungicides and bermudagrass greens, see this article by Dr. Monica Elliot: Bermudagrasses vulnerable to injury from some DMI fungicides.

In this situation, the tebuconazole damage was compounded by uneven application of the product. In the photos above, one can see various patterns of heavy or light application. The application method was similar to below, using a tanksha sprayer and applying the product with a hand wand.

I should give some partial credit to these responses also, for correctly identifying that the application method applied a product unevenly.


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