Powdery Mildew, My Constant Companion

Mushrooms are the darlings of the fungal family.  With relatives like black spot and athlete’s foot, it doesn’t take much to garner praise.  But it’s mushroom’s evil cousin – Powdery Mildew – that takes all the fun out of fungus for me.

Judging by the look of my garden, you’d never guess the depth of my dislike for Powdery Mildew.  It’s everywhere I turn, like an unwanted suitor that can’t take the hint.  I’ve toyed with the idea of declaring the area a theme garden, entitled “Zone de Mycete”, which is French for “Field of Fungus” (everything sounds better in French).  Better yet, I’ll claim the mess as a scientific experiment.  That’s one benefit of having a degree: mistakes/disasters can always be chalked up as research.

It starts with an innocent dusting of white powder on leaves.  In this frosty haze, millions of spores cluster, disrupting photosynthesis.  The spores grow root-like structures, known as haustoria, which feed on the plant’s epidermal layer.  Before you know it, those dusty-looking leaves will be turning yellow.  Then you’ll have dried and brown leaves, and disfigured shoots and flowers.  Attractive, right? 

Amongst the white spores, you’ll find a smattering of black dots.  These are the overwintering fungal bodies, and they are your assurance that Powdery Mildew will return next year, unless you get cracking on some control.  Prevention is the first and best step with mildew, so why don’t you grab the hot dogs and marshmallows and build a Powdery Mildew bonfire?  Composting infected plant material is a big no-no, unless you want your own fungal theme garden.  So rake it up and burn it, or suffer the consequences.

Powdery Mildew doesn’t infect every plant, but there is a good supply of susceptible hosts.  I don’t know if I was subconsciously trying to create a fungal habitat, but I certainly did plant a good number of carriers on the north side of my home.  The first victim was Lilac (Syringa).  Beebalm (Monarda) and Honeysuckle (Lonicera) were the next to go, and Honeysuckle has by far had the worst of it.  Research assures us that Powdery Mildew isn’t fatal, but there are some fates worse than death.

Powdery Mildew on Honeysuckle

Catalpa and Columbine (Aquilegia) joined the party this year, and unless I quit procrastinating, I’m sure more will join in the fun.   Hybridizers are developing resistant strains, so consider that when making plant selections.  I’m aware of a number of resistant cultivars for Phlox and Roses, both of which are highly attractive to fungi. 

Powdery Mildew on Columbine

Powdery mildew lurks in shady spots with poor air circulation.  True to its nature, the epicenter is on the north side of my home.  There, the shade gives fungus a foothold.  However, I can hardly believe that there is poor air circulation there.  We live at the north end of a proposed wind farm and there are few spots on our property not affected by gusty farm breezes.  Apparently, I have a very determined case of PM.  Lucky me. 

When I think of fungus, I think ‘moist and damp’, but Powdery Mildew thrives in a dry environment.  In fact, a daily spray of water from your garden hose will keep it at bay.  Another preventative is a weekly baking soda spray (1 tablespoon each of baking soda, vegetable oil and dishwashing liquid mixed in one gallon of water).  Spray the concoction in the morning, preferably on an overcast day.  A fresh batch must be made each week….no saving the leftovers.  This treatment will prevent mildew from forming and spreading, but will not kill existing colonies.