Brown /rust on leaves of my hydrangea

(Question)

I have brown/rust marks on the leaves of my hydrangea.  It is three years old and in a sunny location.  Do you have any ideas what I can do chemically or naturally to remedy this?

(Answer)

Leaf spots, as you describe them can be a problem on all types of Hydrangeas.  These can be caused by several fungi which typically thrive in the kind of wet weather we have experienced this summer.  Depending on the type of Hydrangea you have, one of several common fungus could be the cause of the rusty spots, so it important to correctly identify your plant.

As these fungi usually only cause an aesthetic problem and rarely kill the host plant, I suggest you try to keep them in check with good cultural practices.   Try this before considering one of the fungicides still available at reputable nurseries under the Ontario Cosmetic Pesticide Ban.  Good cultural practices would include clearing up all plant debris from the ground around the plant, keeping the leaves dry by avoiding overhead watering and only watering early in the day so that any water on the leaves has time to dry before nightfall.  Also, ensure good air circulation around your plants by pruning back neighbouring encroaching plants, and replenishing nutrients in the form of compost in early spring or late fall.