What are Fungi

Fungi are interesting in that they are neither plants nor animals and have their own classification. The main distinction lies in how they feed. Plants make their own food using chlorophyll, sunlight, water, and carbon dioxide. Animals eat and digest food, but fungi neither produce nor eat food. They absorb food by sending parts of their body called hyphae directly into the food where they secrete chemicals that break down the food into a form that they can them absorb back directly into their cells. Unfortunately many undesirable fungi damage plants by absorbing food and water from their hosts.

Fungi are not all bad, and many underground fungi serve important functions, helping plant roots to absorb water and nutrients. Beneficial fungi are also responsible for breaking down the organic matter in soil and compost heaps into usable plant nutrients. Unfortunately harmful fungi also cause most of the diseases likely to be found in the home garden. Many of these fungi reproduce through spores that are blown by the wind making them quite mobile from plant to plant. Other fungi can survive for years in infected soil only to become active again once a host plant is available. Fortunately there are effective forms of treatment for most fungal plant problems.

Steps to Avoid Fungal Disease

Even most chemical treatments for fungus are most effective as preventative measures, rather than fungal treatments, and full blown fungus problems can be difficult to fix. Several steps should be taken to prevent fungal disease:

• Properly space plants when starting the garden to allow for good air circulation and use fans for circulation in greenhouses.
• If a particular garden location has had fungus problems in the past, consider taking steps to amend the soil (described below) before planting.
• Wash and disinfect planting containers before replanting. A 10% bleach and water solution may be used for disinfecting.
• Apply fresh mulch around the base of plants each growing season. Straw works quite well because it is slow to decompose and dries quickly.
• Trim lower leaves of plants to keep them off the ground.
• Water around the base of plants and avoid wetting the leaves.
• While treating infected plants, rake and remove fallen leaves and do not add these to the compost pile.
• In container gardening, move infected plants to a location away from others while treating, and treat the plants in proximity as a preventative measure.

Cornmeal as an Organic Fungicide

Perhaps the best preventative weapon against fungus is common corn meal, and since it is entirely organic, it can be used on edible crops. Cornmeal contains beneficial organisms which are believed to be at least as effective as common chemical fungicides. The interesting thing is how cornmeal works its magic. Cornmeal attracts a good fungus that goes to work in the garden to kill off disease causing fungi. The best way to use cornmeal as a fungi preventative is to work it into the soil at a rate of two pounds for every 100 square feet. This method of application has the added benefit of adding nutrients to the soil.  A cornmeal spray can also be made by soaking one cup of cornmeal in a gallon of water overnight and straining. Food grade cornmeal can be bought at any grocery, but it is much more economical to buy horticultural cornmeal in bulk from local livestock feed stores. One possible source for purchasing corn meal is http://www.soilmender.com/.

Sulfur

Sulfur is commonly used as a fungicide and insecticide. Sulfur can be applied in either dust or spray form, but spray may be the best option because the dust can irritate both eyes and lungs.  As with all foliar sprays, it is best to apply sulfur spray in the morning or evening when the sun is less intense and temperatures are lower to avoid burning leaf surfaces. When using as a preventative measure or as a treatment for diseased plants, sulfur and most other sprays should be used at ten day intervals. Care should also be taken to wet both the top and underside of leaves.

Two popular commercial sulfur sprays:

Safer Garden Fungicide

It comes in a ready to use spray containing .40% elemental sulfur and a concentrate which contains 12%. It is effective at controlling fungal diseases including powdery mildew, rust, scab, brown rot, rose black spot and more on fruits, vegetables and flowers.  Even better, it is OMRI listed for use in organic production. Visit www.arbico-organics.com.

Bonide® Lime Sulfur Spray

This is a combination insecticide and fungicide for use on fruit trees, shade trees, shrubs, roses and berries. Bonide has several effective fungicidal products and information on each can be found at their website: http://www.bonide.com/.

Milk Spray

Is safe and can be particularly effective at treating powdery mildews, downy mildews, scab, and rust. Mix whole milk into a 50:50 solution with water and spray infected plants at 10 day intervals.

Triple Threat SOS Spray – Soda, Oil and Soap

A very effective fungicidal treatment can be made with three common products from the grocery store. To one gallon of water, add one table spoon each of baking soda, vegetable oil (or horticultural oil) and natural dish soap (or insecticidal soap). Many gardeners have been using store bought natural dish soap for years and swear by it and others feel there are advantages to using insecticidal soap available from garden centers. The same goes for vegetable oil verses horticultural oil from garden centers.  

Neem Oil

Neem is a natural extract from the Neem Tree that has a broad spectrum of uses around the home garden as an insecticide and fungicide. Perhaps the greatest benefit of using neem oil is that it doesn't harm or discourage beneficial insects like butterflies, earthworms, and bees. In addition to acting as a powerful fungicide, neem oil makes plants taste bitter so harmful insects do not want to eat them. Visit the following websites to learn more about some popular neem oil formulations:

Arbico Organics http://www.arbico-organics.com/

Neem Tree Farms www.neemtreefarms.com

International Greenhouse Company http://www.greenhousemegastore.com/

The Ahimsa Alternative http://www.neemresource.com/

Potassium Bicarbonate Sprays

Like baking soda (sodium bicarbonate), potassium bicarbonate has strong fungicidal properties. The following are sodium bicarbonate based products:

GreenCure® Organic Fungicide

GreenCure® is a potassium bicarbonate-based fungicide that has been proven to cure and prevent powdery mildew, blackspot, downy mildew, blights, molds and other plant diseases. GreenCure® is as effective as or better than competitive products, can be more economical and, best of all, it's kinder to you and the environment. http://www.greencure.net/.

Remedy By Bonide

Powder Concentrate – Potassium Bicarbonate 85.0%. This is a reduced risk natural fungicide. This food grade bicarbonate provides outstanding control of many fungal diseases including powdery mildew, leaf spots, anthracnose, phoma, phytopthora, scab, botryrtis and other foliar diseases on woody and herbaceous ornamental plants. It contains a spreader – sticker which helps the material adhere to the plant's leaves. Only 1½ - 2½ Tblsp./gal. http://www.bonideproducts.com/.

Herbal Fungicides

A promising new product offers an herbal alternative for treating insect and fungus problems and it smells good too.

Zero Tolerance is a potent blend of herbal oils made from pure food grade ingredients which is environmentally safe. In addition to being an effective pesticide, it is effective on scale, powdery mildew and gray and white mold. Visit www.z-tolerance.com.

Remember that offence is a good defense when it comes to preventing fungus problems. Apply the clean gardening practices listed in this article, and you will be well on your way to eliminating most fungus problems before they start.

Dr. Christopher J. Kline is a master gardener and writer living in Paradise Valley Arizona. Chris is a member of the Garden Writers Association and a columnist for Garden and Greenhouse Magazine www.gardenandgreenhouse.net. You can contact him at This e-mail address is being protected from spam bots, you need JavaScript enabled to view it .