Mildew in the Garden

The spring rains have returned to haunt us in the garden now that the summer humidity is here. Powdery mildew, one of several summer challenges facing our gardens, has arrived.

Powdery mildew is a fungal disease that affects a wide range of plants. It is one of the easier plant diseases to identify, as its symptoms are quite distinctive. Infected plants display white powdery spots on the leaves and stems. The lower leaves are the most affected, but the mildew can appear on any above-ground part of the plant and may spread up and down the length of the plant.

I commonly see it on perennials and annuals this time of year, such as zinnia and phlox. This year it had a very good start with all of our spring rains and I am seeing it on a wide variety of plants, including lilac and amelanchier shrubs. Even my own!

Not to worry though, powdery mildew will not cause permanent damage to your plants. And while there is no treatment at this point, there are a few steps you can take next year to mitigate its reappearance:

  • Keep good airflow around your plants, pruning, thinning and transplanting to maximize the movement of air.
  • Water with in-ground or drip water systems, or only use sprinklers in the morning or early afternoon. Do not water in the later afternoon or evening.
  • Make sure at risk plants are planted with enough bright sunlight to discourage the growth of the mildew.