Using Fungicide for Plants – When and How to Safely Use This Treatment in the Garden

Fungal infections of garden plants can spread quickly and devastate the entire garden. Fungicides are a type of pesticide that kills fungi and prevents the growth of fungi and their spores.

Fungicides used as a protectant can prevent some of the fungal problems common in plants such as hydrangeas, lilacs, garden phlox, and many others.

Once a plant is infected, it may be possible to stop its spread with fungicides, but it will still have the disease. Let's explore more about when and how to use fungicides in the garden.

When to Use Fungicides

Fungicides are often misunderstood in their capabilities and proper use. If you suspect a fungal disease on your plant, do your homework first before reaching for the fungicide.

Fungicides for plants are best used as a preventive to disease. The fungicide is applied at regular intervals as a protectant in hopes of stopping a fungal pathogen from entering your plants. Once the infection takes hold, if you catch it quickly, certain fungicides can kill the pathogen and stop the progression. However, the plant still has the disease. And nothing will stop verticillium and fusarium wilt.

If you have an ongoing fungal problem with a tree or plant, you may want to consider a regular fungicide program the next season to prevent a recurrence. Garden cleanup also helps to prevent reinfestation. Cultural controls can inhibit fungal diseases if you provide the proper sunlight, recommended spacing and location, watering, and fertilization. Choose plants that are bred with resistance to certain fungal diseases. There are many disease-resistant hydrangea and tomato varieties these days and more selective breeding of other plants is helping, too.

Fungicide For Plants In Need

It is important to determine if the issue really is a fungal disease. Online university diagnostic clinics can help, as well as extension offices or your local plant nurseries. It’s best to identify the pathogen so you can select the appropriate fungicide. Once you jump that hurdle, then consider the choices of available fungicides, which are deemed safe if the product instructions are read and followed. It is important to apply the products at the right time and in the right way. Spraying when there is little air movement will help avoid chemical drift.

Fungicides generally are topicals or penetrants. The topicals work as a preventive and stay on the plant as a protective coating to stop the fungus from entering the plant. Its use is repeated when new growth occurs on the plant or the fungicide’s effectiveness erodes through sunlight, rainfall, or wind. Penetrant fungicides move inside the plant (systemic) to stop the infection and prevent its spread.

Here are common active ingredients in fungicides for home landscape use (see brand product labels for list of plants and diseases it will treat):

• Chlorothalonil is a topical for use on many vegetables, ornamentals, fruits, and trees.
• Copper fungicide is mostly topical and is used for a variety of plants such as certain ornamentals, trees, lawn, and some fruits.
• Mancozeb is a topical used for certain ornamentals, trees, and some vegetables.
• Sulfur is a topical used for ornamentals, vegetables, fruits.
• Myclobutanil is a penetrant used for certain ornamentals, lawns, some fruits and fruit trees, cucurbits and some other vegetables.
• Tebuconazole is a penetrant used for ornamentals.

Fungicides work in different ways to stop the fungal disease and they can be used as a mixture or alternately to increase effectiveness and help prevent resistance from developing.

Plants, such as garden phlox, monarda, and lilac shrubs are notorious for getting powdery mildew each year. In those cases, it can help to spray a topical fungicide as a preventive. It can be sprayed on the leaves where it remains as a protective coating. (Lilacs get powdery mildew often, and though the leaves may look unsightly, treatment is not really needed.) Many rose cultivars, especially hybrid teas, routinely get black spot disease if they are not on a fungicide program.

Topical fungicides for the vegetable garden should be applied often enough to cover new growth and during periods of wet weather. Some vegetables, like tomatoes, can grow quickly in a week, so the new growth is vulnerable till you spray again. Lawn fungicides also need repeat applications because the fungicide is removed as the lawn is mowed.

A fungicide spray on fruit trees before leaves open in spring can alleviate many fungal disease problems. Look for the fruit tree name on the product and follow all spraying instructions.

Homeowners battling fungal diseases on large, shade trees that are out of their reach may need to consult a professional applicator to apply a fungicide for trees.