Powdery Mildew

Powdery Mildew starts out as whitish spots that spread quickly until the entire leaf is covered. The white powdery growth is a fungus that with time becomes gray to tan/brown felt like patches. Leaves may become stunted, curled, chlorotic and eventually wither and dry up.  powdery mildew

Moderate temperatures and high humidity help develop the disease. The pathogen also favors hot days, cool nights, high humid (85%)  conditions and the change of season. Each mildew pathogens is specific to its host, the mildew that attacks gerbera daisy will not spread to cucumbers.

powdery mildew on zinnia

Fungicide treatments and preventative controls

Depending on the severity, spraying it with a baking soda formula is effective as a preventative when applied regularily.  For active infections spray daily for a week.

1. Mix 1 TBsp each of  baking soda and horticultural oil (dormant oil/vegetable oil) or a few drops of liquid soap to 1 gallon of water.  Spray weekly making a new mix each time.  It will not elliminate the disease but help control it.

2. Mix 1 tsp baking soda with a few drops of vegetable oil in 1 quart of water. Spray or paint on the leaves.  Works on houseplants, cucurbits & roses (balck spot).

3.Another suggestion is  a solution of 1/3 milk and 2/3 water and spray on plants. Use every other day.

4.I also heard of mixing 1 tbsp of pine sol to 1 gal of water as a mildew spray.

Neem Oil is also affectective in controling powdery mildew infections. Use 1 oz (2 Tbsp) of Neem oil and 1/ 1/2 tsp of dishwashing detergent to one gallon of water. Spray once a week for two weeks. A combination of Neem oil and baking soda is the safest control method.

Chemical Fungicide sprays

Use chemical sprays such as Benomyl (systemic fungicide) sulfur/fungicidal soap or Safer’s garden fungicide. Spray early in the growing season as a preventative or as soon as symptoms appear.
A synthetic fungicide Baylaton sold as Strike also works on powdery mildew.

Always follow label directions, to make sure the product is approved for specific plants.  Early detection works best. Once the disease takes hold, it is difficult to control.

Cultural preventatives 

- remove the infected leaves
-do not crowd the plants
-provide good air circulation
- keep plants well watered and stress free
-grow resistant plants when available
-avoid  fertilizing with too much nitrogen - succulent new growth can be succeptible .