Fungicides are a great tool for homeowners and farmers. Fungal pathogens are one of the three main pests that impact plant health. Fungicides can prevent or stop them. There are hundreds of fungicides registered for use on all sorts of plants and fungi.
In this article, we cover everything you need to know about fungicides. We will also cover some of the most common fungal pathogens and which fungicide to use against them.
What are Fungicides?
Fungicides are chemical compounds that can kill fungi and their reproductive spores. There are both organic and inorganic fungicides available for use. Man made fungicides have also been developed to help control plant-damaging fungi.
Fungicides are a type of pesticide and may simply be referred to as pesticides. To buy and use some pesticides you need a license.
Types of Fungicides
There are many differences among fungicides used for plants. They have different active ingredients, forms, and formulations. Different active ingredients work to treat specific fungi. Various forms include sprays, wettable powders, and granules.
Lawn fungicides, tree fungicides, and garden fungicides have different formulations. A fungicide labeled grass fungicide often can’t be used for trees due to its formulation.
Contact fungicides work by being sprayed directly on the fungi to kill them. Systemic fungicides translocate into the plant’s tissues. There they can prevent or stop a fungal infection from spreading. Some fungal diseases have both contact and systemic fungicide control options.
You may need a license to buy certain fungicides. For example, Serrata fungicide for controlling Pythium can only be used by professionals.
Below is a table with some of the most common fungicides you’ll find at garden centers. It lists the active ingredients, some brand names, and if they’re contact or systemic.
|
Active Ingredient |
Brand Name |
Contact or Systemic |
| Chlorothalonil | Bonide Fung-onil, Daconil Fungicide, Ferti-Lome Landscape & Garden Fungicide, Ortho Garden Disease Control | Contact |
| Copper hydroxide | Hi-Yield Copper Fungicide Kocide 101 | Contact |
| Copper salts | Bonide Liquid Copper Fungicide | Contact |
| Myclobutanil | Spectracide Immunox Multi-purpose Fungicide | Systemic |
| Neem oil | Ferti-Lome Triple Action RTU | Contact |
| PCNB (Pentachloronitrobenzene) | Terraclor 400 | Contact |
| Phosphorous acid | Monterey AGRI-FOS | Systemic |
| Propiconazole | Banner MAXX, Ferti-Lome Liquid Systemic | Systemic |
| Sulfur | Bonide Sulfur Plant Fungicide, Hi-Yield Wettable Dusting Sulfur, Monterey Sulfur 90W | Contact |
| Tebuconazole | Bayer Disease Control | Systemic |
| Thiophanate-methyl | Cleary’s Systemic Fungicide 3336, Scotts Lawn Fungus Control | Systemic |
Fungicide Uses
The main use of fungicides is to stop the growth of fungi and their spores. They’re often used in agriculture and residential areas on fungi that infect plants.
Certain fungicides can be used to treat fungal infections in livestock or humans.
Fungicide Application Rate & Frequency
The application rate and frequency for every fungicide are different. This includes products with the same active ingredient. The plant and fungi being treated will also impact the application rate of a fungicide.
Reading the entire label of the product you buy is extremely important. This helps you to determine the appropriate application rate and frequency of use. The label also provides critical safety information you should always follow.
Fungicides can be applied in a variety of ways depending on the product’s formulation. Granular fungicides and ready-to-use (RTU) fungicide sprays are the most common. They are also the easiest to apply. Bioadvanced fungicides and Bonide fungicides are two common brands that sell RTU products. Other formulations types include:
- Dispersible Granules (DG)
- Dry Flowables (DF)
- Dusts (D)
- Emulsifiable concentrates (EC)
- Flowables (F)
- Fumigants
- Water Soluble Pouch (WSP)
- Wettable powders (WP)
Note, to use some of these formulations you’ll need special equipment or licensing.
It’s important to follow the recommended application rate and frequency when using fungicides. These guidelines have been developed to ensure that the product works correctly. Over-application can damage plants and the ecosystem, such as local waterways. Over or under-application of fungicides can also lead to fungicide resistance.
Fungicide Side Effects
Phytotoxicity is an adverse side effect to plants by chemicals. Fungicides can cause phytotoxicity when they are not used properly or used at the wrong time. Phytotoxicity can cause plant metabolic, growth, or other physiological issues.
Symptoms of phytotoxicity include discoloration, distortion, stunted growth, and plant death. To prevent phytotoxicity, follow all application directions on the product label exactly.
Resistance is another issue that can arise from improper fungicide use. When a fungus develops resistance to a fungicide, the fungicide will no longer work to control it.
There are a few ways to prevent fungi from developing a resistance to fungicides. First, you should make sure you use the correct application rate. Second, make sure you apply it again only if the instructions say to.
It is also a good practice to rotate fungicides with different modes of action. This decreases the chances of resistance developing.
Misuse of fungicides can also cause issues in the environment. Waterways are harmed the most due to runoff. Chlorothalonil is toxic to many different types of aquatic animals. Copper sulfate found in some fungicides is toxic to bees. Make sure you follow fungicide directions to avoid negatively impacting the environment.
Most fungicides are not considered very dangerous for human health. Some can cause skin or eye irritation on contact[1]. Others can lead to coughing and lung irritation when inhaled[1]. No long-term side effects from fungicide exposure are known but research is ongoing.
Some fungicides have a higher risk of impacting environmental or human health. You’ll need a pesticide license to buy and use them.
Common Plant Diseases Caused By Fungi
There are all sorts of fungi that can negatively impact plant health. Some fungi are only present in certain regions, and some only impact specific plants. But, a handful of fungi are widespread and are common problems for gardeners.
The table below shows the most common types of plant fungi, their symptoms, and treatments.
| Fungi Name | Symptoms |
Treatments (active ingredient) |
| Armillaria rot | Foliage wilted (hanging downward), yellowing leaves, leaf drop, branch dieback | PCNB, thiophanate-methyl |
| Botrytis blight | Irregular bud and flower development, irregular brown spots on flowers, quickly rotting flowers | Chlorothalonil |
| Crown rot (Pythium spp.) | Foliage wilting, stunted growth, asymmetrical growth | Phosphorous acid |
| Downy Mildew (water molds) | Light green or yellow angular shaped pots appearing on the upper leaf surface, white fungal growth on the underside of leaves below spots. | Chlorothalonil, copper hydroxide, copper salts, phosphorous acid |
| Leaf spots (Alternaria, Anthracnose, Cercospora, Heterosportium, Septoria) | Spot color, and size vary depending on which pathogen is present. Spots can be black, brown, tan, reddish, or purplish and have a dark margin. | Chlorothalonil, propiconazole |
| Powdery Mildew | White, powdery fungi growing on the upper leaf surface. May cause irregular spots on leaves. | Chlorothalonil, myclobutanil, neem oil, sulfur |
| Rhizoctonia root rot | Lesions on stems near the soil surface that appear dry and sunken. Lesions on the stems and roots cause plants to yellow, wilt, or become stunted. | PCNB, thiophanate-methyl |
| Root rot (Phytophthora spp.) | Symptoms resemble drought stress including yellowing leaves and leaf drop. | Phosphorous acid |
| Rust | White, black, brown, orange, or yellow pustules on the lower leaf surface. | Chlorothalonil, myclobutanil, tebuconazole |
Beneficial Plant Fungi
Not all fungi are bad for plant health. Certain fungi benefit plants. For instance, mycorrhizal fungi develop on plant roots forming a symbiotic relationship. The plant provides the fungi with sugars. In return, the fungi help by increasing the uptake of water and mineral nutrients by the plant.
Fungi in the genus Trichoderma attack and prevent other fungi from infecting plants. Many companies sell these fungi as biocontrol agents for plant fungal diseases.
Other fungi that can be used as a biocontrol agent include Arthrobotrys dactyloides. It parasitizes and reduces certain plant nematodes.
Fungicide vs Pesticide vs Herbicide
The main difference between fungicides, pesticides, and herbicides is what they work on. Fungicides kill fungi, while herbicides kill plants.
Fungicides, herbicides, and insecticides are all specific types of pesticides. Pesticides tend to have a bad reputation. This is due to the negative impacts they can have on the environment and human health when misused. For example, the book Silent Spring published in 1962 shed light on the impacts caused by the use of DDT.
Pesticides have come a long way since then. Most don’t cause adverse effects as long as users follow their instructions for use. Pesticides now work on specific biological pathways only found in the target organism. This prevents negative impacts on non-target organisms.
For example, some selective herbicides interrupt the C4 pathway. This pathway is only found in some plants like grasses. This allows them to kill unwanted grass-like weeds without killing broadleaf plants.
Any time you use a pesticide, you should first read the label to make sure you use it for the right situation. If you want to get rid of aphids on mums, you should only use a product registered to kill aphids on mums. Always follow the label directions exactly. This helps you avoid damage to your plants, the environment, and yourself.
References:
[1] Lorenz, E.S. (2022). Potential Health Effects of Pesticides. The Pennsylvania State University, PennState Extension.