fungus on Yarrow?? Please advise!!

Asked June 9, 2020, 5:11 PM EDT

I have a Yarrow (Achillea Gold Coronation) devastated by something making the leaves brown. Is this a fungus? I'm assuming it cannot be treated since damage seems so extensive. Or should I try to treat it? If so, with what should I treat it. Next to the Yarrow, I have a Monarda, with a couple damaged leaves. Do you think the Monarda is affected by the same thing as the Yarrow?

Montgomery County Maryland

1 Response

We cannot say for sure what is going on with the plants. We notice that the soil and mulch looks wet around the base of the plants.

At this point we tend to think that this may be an abiotic issue and not disease related. No chemical controls are recommended.
It is possible the plants may be overwatered and there is too much mulch around the base of the stems. Yarrow likes a well drained soil on the dry side. Monarda grows best in a moist well drained soil but can handle more moisture than the yarrow.

Do not overwater. Check the drainage in the area and make sure mulch is no thicker than several inches and away from the base of the stems. Let the yarrow flower, and then cut back to healthy foliage, and remove any damaged foliage.
Monarda - pick off any damaged foliage. Monitor the plants and you can send us more photos if you notice additional symptoms.