Tom's Blog

Monday, April 23, 2012

Indian grass: Major frost damage

On the early morning of April 12, 2012 much of the Indian grass (Sorghastrum nutans) at Pleasant Valley Conservancy suffered major frost damage. Most of the south slope as well as the mesic and wet-mesic prairies below Pleasant Valley Road were seriously damaged. The south slope looked like it had been sprayed with glyphosate! The photo above is typical.

None of the cool-season grasses seem to have been affected. Also, other warm-season grasses such as little bluestem, prairie dropseed, and big bluestem are apparently fine.

The early warm weather was certainly responsible. Warm-season grasses such as Indian grass generally do not start making significant growth until mid-May, but the unusual warm weather this spring got everything started early. After our very early burn on March 13, there was over a week of very fine weather, and Indian grass had a chance to get started well.

The freeze that hit the Indian grass was probably early in the morning on April 12. I don't have good temperature readings for PVC, but the temperature dropped to 24 F at the nearest available weather station, at Lone Rock, Wisconsin. The micrometeorology of the south slope is complex, and only the lower more open parts seemed to be affected. However, the planted prairies below Pleasant Valley Road really took a hit. (The photo above was taken in the Crane Prairie.)

We did not actually notice the effect until a week later, when all of the lower part of the south slope had patches of brown. I am not sure why Indian grass was particularly hit, but in general warm-season grasses are quite cold-sensitive.

 Most of the forbs did not seem to be seriously affected, although as the photo here shows the edges of the leaves of prairie dock were noticeably brown. This was the only Silphium affected, as compass plant, cup plant, and rosin weed seemed fine.

We haven't lost our Indian grass for good. There should be plenty of dormant buds that survived the frost and will start growing. However, growth will certainly be delayed and it will be interesting to see what our Indian grass stands will end up looking like this year.

I did an extensive literature search but was unable to find any research on the cold-sensitivity of  Indian grass.

Prairies and savannas are not the only areas affected by the early warm weather this year. Fruit-tree growers have also suffered. And maple syrup production was almost zero.


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