Black Leaf Spots on Sweetgrass
Answered by: Conrad Richter
Question from: John Reed
Posted on: August 9, 2003

The sweet grass I ordered and planted has developed little pin head size black spots that are rounded and hard on the leaves. Any ideas as to what this is and what to do about it. The plants have really spread and are growing well other than these spots.

The spots are most likely a symptom of a fungal disease. There are many leaf spot diseases that attack grasses. We have never seen this black pinhead-like disease on our sweetgrass plants so we cannot offer any advice based on first-hand knowledge of the problem. I checked all of our plant disease sources but nothing turned up for Hierochloe odorata (sweetgrass). I suspect that because sweetgrass is a wild plant of little economic importance (except to American aboriginals) little is known about the diseases that attack it.

You have several courses of action available to you:

1. Send a leaf sample to your local agricultural or horticultural extension office. Many extension services in the United States will arrange for experts to diagnose plant diseases. Even if the extension service is not familiar with the host plant or the disease, they may be able to identify the fungus using diagnostic keys. Sometimes plant diseases are quite common, attacking many species of plants, and your local expert may recognize it as one that attacks other grass species in your area.

2. Do nothing. Some diseases are self-limiting, meaning that they clear up on their own. They may manifest because so unusual enviromental conditions such as drought or excessive rain. Or, they may not be damaging enough to warrant heavy intervention with chemical fungicides that may put people and animals at risk.

If you do decide to have the disease identified please let us know what the diagnosis is.

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