Powdery Mildew

Powdery Mildew

Disease Description:

Powdery mildew is a fungal disease which is known to affect a wide variety of plants including those grown in the home and home garden. Many types of fungi are known to cause powdery mildew but two main ones, L. taurice and S. macularis, are responsible for most powdery mildew outbreaks for the home gardener.

Symptoms and Damage:

Powdery mildew is one of the easiest diseases to spot making it somewhat easier to treat. This disease is characterized by white powdery spots on the stems and leaf surfaces. The heaviest areas of infection will be on the lower leaves but can be appear anywhere on the plant.

Growth of the plant will be diminished as the light intake of each leaf will be interrupted by the powder like coating the mildew causes. Leaves may become misshapen and turn yellow with few green spots. Premature leave drop of infected plants can be expected.


Powdery mildew favors an average temperature range, it grows and spreads rapidly in the range of 60 to 80 degrees. The fungus will tolerate a wide humidity range growing rapidly in the moderate range, thriving in warm shaded places. It is not affected by water but can be damaged by strong blasts of water, though this is not a valid method of control.

First Aid for Powdery Mildew

There are many benefits to avoiding chemicals when dealing with plant diseases. The harsh chemicals in some fungicides may cause more harm to an already injured plant not to mention the possible harmful effects to you or your loved ones.

First choices for attempting disease control.

Used when green don't solve the issue.

Only use when blue options have failed and the plant cannot be discarded.

Prevention– The best prevention for powdery mildew and fungi in general is proper maintenance, remove dead and decaying material for the compost around your plants and regularly inspect them. Proper watering and air flow will do wonders to help control outbreaks of fungus in your houseplants and gardens.

Manual– Heat can be used to kill the fungi responsible for powdery mildew but it involves raising the plants temperature to 100ºC, this can be dangerous for a sick plant. It is recommended to do so at the end of a growing day in darkness while keeping the roots cool. The best manual method is removal of the infected areas of the plant or the plant itself if the infection is really bad. The removed material should not be composted as the fungus can live in the composted material and pass to other plants.

OrganicGarlic Spray, Neem Oil Spray, Milk Spray, Cinnamon Oil Spray, Orange Peel Spray, Baking Soda Spray and Hydrogen Peroxide Spray can all be used, with success varying on the strain of fungus that has caused the mildew in the first place.

Biological– A few biological applications are available to the home gardener, two main ones are Serenade® and Sonata®. Ask about them at your local garden center or hardware store.

Chemical– A few chemical fungicidal sprays exist for commercial and home gardening, ask at your local garden center or hardware store. Chemical controls works best is the infection is detected early and you are diligent in your control measures.

More information on Powdery Mildew:

Wikipedia - http://en.wikipedia.org/wiki/Powdery_mildew

Colorado State University - http://www.ext.colostate.edu/pubs/garden/02902.html

Identification of Powdery Mildew - http://www.apsnet.org/edcenter/PowderyMildew.aspx