Monthly Turfgrass Roundup (April 2014)
A note on light and grass selection in warm-season areas

Turfgrass Mystery: the case of the island incident

This mystery comes from the Westman Islands. For an overview of turfgrass in Iceland, see this report and these photos.

When I visited the Westman Islands GC, most greens looked as above. The grass was healthy at the end of summer. But there were a couple greens that had some bare areas, as shown below.

Green1

A closer look at the bare areas revealed this appearance.

Green2

The mystery is this: what caused the grass to fail in some areas? I wouldn't wish this pernicious problem on anyone.

The answer is nematodes, and Dr. Brett Morris identified exactly what has happened:

 Partial credit for a right answer goes to Nadeem Zreikat from Campbell Chemicals, who guessed disease or nematodes, which I didn't think was specific enough. If you click on the photo above, you will see the bare area has Festuca rubra growing in it but not Poa annua, although one can see a few plants of Poa annua in the surrounding areas. 

In looking at the root system of the Poa annua, one can find root galls caused by Subanguina radicicola.

Gall

The nematode damage to the root system of the Poa annua makes it more susceptible to stress, especially when the grass is maintained with low nitrogen applications to favor the desired Festuca rubra.

 

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