What to do about powdery mildew

Q:  I’m seeing that white, powdery mildew developing on the leaves of my peonies, garden phlox, lilacs, roses, squash.  Should they be treated and what is safe to use?

A:  Powdery mildew is a fungus, an opportunistic, but seldom fatal garden disease.  Mildew favors warm days and cool nights that result in dew on the leaves.  Moisture from overhead sprinklers can also contribute.  Good cultural practices to discourage mildew include:

• Proper sunlight.  Sun loving plants grown in the shade will be weak and  vulnerable. 
  

• Keeping foliage dry.  Water at the soil level rather than overhead.  If you must water with overhead sprinklers, do so during early morning hours so the foliage will dry quickly. With evening watering the foliage stays wet all night.
  

• Air circulation is important.  If plants are too crowded, air doesn’t circulate well which will favor mildew development.  Prune crowded plants to encourage better air circulation or make plans to move plants farther apart the next year.
  

• Some plants are just prone to mildew regardless of cultural efforts.  Monarda, some varieties of garden phlox, peonies, lilacs, and squash to mention a few.  First examine and correct your cultural practices. 
  

GreenCure is probably the safest organic fungicide. It’s registered “For Organic Production” and it works.  Prophylactic applications of sulphur or copper fungicides BEFORE the mildew shows up are another method of controlling chronic mildew issues, but be careful not to overapply. 

To repeat, powdery mildew rarely kills plants.

Keith Funk is handling our Q & A this year. You may have visited one of Keith’s Denver area gardens on a tour or know him from his years at Echter’s and now at Nick’s Garden Center. For 30 years he’s been heard every Saturday morning from 7-9 with fellow Wise Guy, Jim Borland, on the Garden Wise Radio Show on Legends 810AM.