Powdery Mildew on Garden Sage: What to do

A Garden Sage Dilemma

When powdery mildew arrives on garden sage, what can be done? After all, you grow your sage to be consumed so why would you want to treat it with fungicide and thereby plan on consuming chemical residue.  If left untreated, the plant will likely succumb to the disease.

The Diagnosis

Powdery mildew on garden sage appears as the temperatures increase in late spring. It is a fungal disease.  In the early stages, it looks like dusty white spots on the upper surface of the leaves.  As it develops, entire leaves will be coated with the fungus and it leads to leaf drop and deformed new growth. Untreated, it can eventually kill the plant.

Good Cultural Treatment

Prevention of disease is always the best first step.  Ensure that sage is planted in a full sun situation with good soil drainage and excellent air circulation.  In the case of powdery mildew on garden sage, good air circulation must be continually monitored.  Poor pruning habits can lead to dense foliage which is a problem: instead of taking the tips of many the branches for culinary use, take a few branches entirely.  This will lead to a more open plant and allow for better air flow.  If you see the first signs of powdery mildew, pluck affected leaves individually and then assess the plant as a whole, it may need thinning.

Emergency Measures

If you find that you are fighting an epidemic of powdery mildew on garden sage, there are a few relatively safe treatments to employ. Numerous fungicides are rated for use against powdery mildew, but keeping in mind that you want to eat the leaves you will want to select wisely. A few safe bets from the garden center include neem oil, sulfur dust, or the biological fungicide Bacillus subtilis (Serenade Garden Disease Control).  These treatments are proven effective against powdery mildew and leave very little residual effect once they dissipate.  Keep in mind, these applications should not take the place of good cultural practice.  Always ensure good preventative maintenance, even when treating with a fungicide. This will minimize the amount of treatment needed to cure the problem.

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