We've recently done a couple of quite lengthy posts about preventing fungal infections in your vegetable garden (see Part II as well). This time, we want to talk about some of the sprays and other treatments that can also be used by an organic gardener to deal with fungal diseases.
Biofungicides: Biofungicides and biopesticides are increasingly used as part of the organic gardener's toolset for dealing with crop pests. In both cases, they employ common bacteria, or fungi themselves which can either kill or contain plant pests and diseases. Apparently, the pests cannot develop resistance to biological pest controls as easily as they do for chemical controls, and so in using them, we're not contributing to the development of any scary, multi-resistant superbugs of the garden!
Biofungicides work in a variety of ways to combat plant diseases: they can directly compete with other soil fungi, creating a protective barrier around the roots of plants that prevents harmful fungi from getting at the plant roots. They can also work by "antibiosis," where the fungus produces its own antibiotics (remember penicillin mold?) to kill soil bacteria. Biofungicides can also predate the pathogen directly, attacking and eating it. And finally, they can stimulate the host plant to activate its own defense mechanisms, thereby resisting the fungus for itself.
It's pretty cutthroat in the fungal world!
A few commonly available biofungicides:
- Serenade garden spray contains bacillus subtilis, which works both to prevent and treat fungal garden diseases. It works against many fungi and bacteria in the garden, is safe for food crops, and is certified for organic growing use in many countries.
I am not completely versed in the uses and strengths of Serenade, but my understanding is that while it can help to contain an existing fungal infection on the leaves and stems of a plant, it is still more effective as a preventative. For this purpose, it should be sprayed on garden plants (cover all surfaces) once every 7-10 days throughout the growing season.
You can get Serenade at most garden stores. It comes in a spray bottle, ready to use, or in larger, concentrated quantities, if you expect to need a fair bit over the season.
- Safer's fungicide is also used in organic gardening, falling back on the tried and true ingredient of sulphur to do its work. It's good for powdery mildew on a variety of crops. Some mineral fungicides like copper should only be used as a very last resort (if at all), since they are just too harmful to all kinds of beneficial micro-organisms as well as the unwanted ones. But sulfur is seen as causing few environmental concerns.
Safer's products are also available at garden stores, and after extensive research into a variety of Safer's products, I have been pleased to see that all or most seem to accord with organic practises - their well-known insecticidal soap, for instance. Their garden dust is a biopesticide, making use of bacillus thuringiensis to parasitize caterpillars and leaf-feeding worms.
Myke, best used when first planting bedding plants or seeds, is a powder that you mix into the soil beneath. It contains a myccorhizal fungus (ie: symbiotic with plant roots) which occurs naturally in the soil, but which has been badly depleted in the disturbed or over-fertilized soils of most settled areas.
Myke both protects plants from other below-ground fungal infections, and enhances the capacity of the plants to take up such nutrients as phosporus, copper and zinc.
Other organic fungicides:
- Baking soda spray is a longstanding fungicide against powedery mildew. It works by raising the pH on the leaf surfaces, creating an inhospitable environment for the mildew to grow. A common recipe usually goes like this: mix a tablespoon of baking soda and half a tablespoon of vegetable oil (to keep the soda on the leaves longer) into 2 liters (quarts) of water.
Essential oils: over the years, I've heard about a variety of essential oils which are thought to have antifungal properties when sprayed on plants. These include oils from caraway, clove and thyme (above). I haven't tried these, but I assume you mix a small amount into warm water and shake it thoroughly, and often, while you spray it on the foliage of a plant.
I have been using essential oils as insecticidal sprays, though: peppermint, rosemary (right), scented geranium and citrus oils. I mix small amounts of some or all into an appalling concoction I call "vampire juice," because it also uses pulped garlic (strain the garlic out before spraying). Mix this up with a bit of dish soap, and it works well against aphids, white flies, and the like.
Lots of other options are out there, from home remedies using skim milk as a fungicide to other biofungicides used by commercial growers. If you want to do more research, though, you'll find yourself browsing lots of marijuana grow pages - count on them to be on the cutting edge of these things!