Zone 5
Mature Perennial garden, morning sun, mid-afternoon shade. Soil is clay, but I have amended it in recent seasons with sheep manure.
Very wet, cold spring this year.
Leaves of Shasta daisies, brown-eyed Susans and coneflower are either covered in small brown spots, or being devoured by some pest (full of holes). See picture below of brown spots. Please advise what I am dealing with and how to best save my plants. Could they be two separate issues?
Thank-you for consulting Toronto Master Gardeners.
Without a photo of the leaves with holes, it is difficult to be certain, but it is likely that all of the damage you are seeing on these perennials is caused by some kind of leaf spot. This can be either a fungal or bacterial disease. It is not always possible to tell the difference with the naked eye. One of the fungal ailments common to the 3 plants you have named is septoria fungus. This causes round or irregular spotting which can sometimes spread into blotches taking over the whole leaf. Spots can cause the leaf matter to die out causing holes in the leaves.
The cool, wet weather of the Toronto spring were ideal for the growth and spread of fungal infections. Mature gardens such as yours can be prone to fungal spread because they often have poor air circulation.
Fungicides can be useful, but they are a preventative rather than a cure so not really useful in your situation. The best approach is to ensure good air circulation by pruning plants back so that foliage can dry off. When watering, try not to splash water on the foliage. If a large percentage of the leaf mass on the plants is infected, you can cut back the plants, but this is not usually necessary. Most often, the perennials will withstand the onslaught and just suffer the problem of unsightly leaves.
The following link provides some general information about leaf spot and other fungal diseases: