Catching up with an old edition of Gardener's Question Time (8th June), Christine Walken recommended spraying mild rust (and powdery mildew) with a solution of one tablespoon of baking soda in a gallon of water.

I was wondering if anyone had tried it and whether it was successful or not?

Googling for it turned upthe article below - whcih seems to agree with the addition of a small amount of soap - perhaps to break the surface tension?

Baking Soda Recipe for Controlling Powdery Mildew on Plants

A Home Remedy for Fungus Diseases

By Marie Iannotti, About.com Guide

See More About:

• pesticides
• plant problems
• organic gardening

Powdery Mildew on Phlox

Marie Iannotti

Baking soda makes an inexpensive control for powdery mildew on plants. The baking soda fungicide is mostly effective as a preventative, offering only minimal benefits after your plants have become infected. Weekly spraying of susceptible plants during humid or damp weather can greatly reduce the incidence of powdery mildew in your garden.

To control powdery mildew on plants, mix together:

• 1 tablespoon of baking soda
• ½ teaspoon of liquid soap
• 1 gallon of water

Do not store unused mixture. While this recipe has been known to be effective, it can burn the leaves of some plants. It is recommended that you water your infected plants well a couple of days before applying this mixture, and don’t apply it in full sun. Try on a small area first, to test the plant’s response before spraying the entire plant.

Some recipes also recommend applying 1 tablespoon of ultralight horticultural oil to the mixture. The oil coats and smothers the fungi. The soap is added to help the mix spread and cling to the leaf surface. Be sure to apply to lower leaf surfaces as well.

Researchers are still studying the effects of using a baking soda mixture on other fungal diseases such as: black spot, rust and anthracnose.

More on Dealing with Fungal Diseases

• ontrolling and Preventing Powdery Mildew on Plants
• Using Cornmeal as a Garden Fungicide