How to Prevent and Treat Powdery Mildew 

For any of us that grow close to the coast or in areas that get lots of morning dew or cool summers, powdery mildew is all too familiar.  It is a white (sometimes slightly grey) substance that looks like dust on the leaves.  It typically shows up on the underside of the leaf first, then spreading to the entire plant.  Powdery mildew is a fungal disease caused by many different strains of fungi. Fungicides can be used to as a treatment but we here at San Diego Seed Co. like the old adage “an ounce of prevention is worth a pound of cure”.  Meaning, we like to understand why something occurs in the garden or on the farm and then try and prevent it from happening in the first place. We are lucky enough that many times we can produce a whole seed or food crop with no insecticides, fungicides or any sprays”. This is because we are so keen on prevention.  Here is what to know about powdery mildew.

Unlike the common misconception powdery mildew does not need moisture to continue to grow. In fact, you will notice on your squash plants that it is actually the end of season that the plant gets really infected with powdery mildew.  Here are our prevention measures.

  1. Always grow the plant in a sunny location
  2. Provide good air circulation by pruning excess foliage- this is our number one prevention measure for a wide range of garden issues
  3. Don’t over fertilize as this causes excess foliage growth
  4. Don’t overhead water- this is our number two prevention measure for a wide range of garden issues

Ok, so you have powdery mildew, now what do you do?

You can prune off infected leaves from many veggie and flower plants. These should not be composted! You should also practice good garden hygiene and disinfected your pruners after cleaning out infected plants.  Another common suggestion is that you can “wash” off the spores in the midmorning. This is very true but some considerations should be made so that it does not lead to more damage. This is only recommended for areas that warm up during the day. If you live on the coast this must be done on a very warm sunny day. Inland areas have more days of the year like this.

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