How to Identify Garden Fungus Infections

Garden fungus infections are common problems throughout the U.S. according to the Centers for Disease Control and Prevention (CDC), they affect nearly 300 million Americans yearly. Unfortunately, most gardeners don't realize that fungi are responsible for much of the mildew and mold growth in their yards and gardens.

In addition to molds, yeasts, bacteria, algae, and other microscopic organisms, fungi cause fungal diseases. These organisms thrive in moist places and feed off dead organic matter such as leaves, lawn grass clippings, and fallen fruit.

Common symptoms include dark spots on plants, wilting, leaf drops, or discoloration. Read on to learn how to identify and control that fungus.

What is a garden fungus?

What is a garden fungus?

A garden fungus, also known as an earth-dwelling mushroom or mycetozoa, is any of thousands of tiny fungi living in soil and decomposing organic matter.

Fungi are among the most important organisms on Earth because they recycle much of the carbon from dead plant material back into food for other plants.

Without these microscopic, unseen allies, our world would quickly become uninhabitable. Some species of fungi even produce enzymes that break down toxic chemicals and pollutants.

Fungi can cause serious damage to trees, shrubs, flowers, vegetables, fruits, and turf. They may infect plants when there is too much moisture around roots, resulting in rotting and death. Other times, fungal spores drift through the air and land on plants, causing disease. Click here to know how to treat and control fungus in your vegetable garden.

The best way to protect your landscape and keep it healthy is to maintain a well-maintained lawn and garden with regular fertilization. This helps prevent the buildup of nutrients in soils that allow harmful microorganisms to flourish.

Fungus in the garden: what causes it?

Water sitting on leaves often causes fungus diseases. Remember to "water the pot, not the plant." Rather than watering the leaves and foliage of the plants, water the soil instead. This prevents fungus spots on the leaves and foliage and wastes water.

If you are growing your own plants indoors or outdoors, be sure to keep them well-watered. A lack of water can cause root rot in plants. In addition, you must check your plants regularly to ensure they don't have any signs of disease. If you notice any problems, contact a local nursery for help.

Here are the 10 most common garden fungi and their symptoms:

1. Armillaria

Avocado roots and trunks rot due to Armillaria, a soil-borne fungus. Before any symptoms are seen above ground, the fungus can establish itself well in the roots and the root crown.

After infection, young trees often die rapidly. Infected trees usually die prematurely. However, the condition for growth and disease development may improve temporarily, resulting in the death of mature trees or their recovery at least temporarily.

Symptoms of Armillaria root rot usually include wilted, downward-hanging foliage. The foliage yellows leave a drop, and the upper limbs die back as well. It is common for Armillaria-infected trees to grow groups of short-lived mushrooms during the rainy fall and winter.

Fungal growth in cambial tissue is the most reliable sign of Armillaria root rot. Identify Armillaria mycelium at the base and crown of trees that exhibit aboveground symptoms of infection.

A strong mushroom odor is associated with the fungus mycelia, which is white. The inner bark and cambium typically grow in patches. Throughout the diameter of large roots, an infection can occur.

2. Black spot

The black spot will be particularly familiar to anyone who grows roses. A black, grey, or brown spot will appear on your plant's leaves and cause them to drop.

If it happens, remove and destroy any infected leaves, and take care to ensure none are left behind come autumn. Apply a fungicide spray on roses to prevent recurrence; for everything else, spray a fungicide.

3. Powdery Mildew

Many ornamental and landscape plants are susceptible to powdery mildew, which is a fungus. It is caused by a type of fungus called Erysiphe cichoracearum. Powdery mildew causes unsightly, whitish patches on leaves, shoots, and fruit.

These spots are often difficult to see because they look like dust. Powdery mildew is spread mainly by windblown spores. In some cases, people move infected plants from place to place and unknowingly carry the pathogen along.

The most obvious symptom of powdery mildew is the appearance of white, fluffy growths on the upper surfaces of affected plant tissues. Leaves, petioles, and stems are particularly susceptible to infection.

When you examine a leaf under magnification, you may notice small, round yellow dots scattered over the upper surface. These are actually tiny conidia, microscopic structures produced by the pathogen.

Conidiophores, another part of the organism, sprout from these dots and produce additional conidia. As the disease progresses, the entire leaf becomes covered with white fuzz. White mycelium grows out of the leaf tissue and eventually covers the whole leaf.

Affected parts of plants may wilt or turn dry and brittle. This can lead to loss of productivity and eventual death. A good rule of thumb is to avoid moving infected plants until after the weather has settled down. Once the weather turns cold, it's best to immediately move the plant indoors.

4. Leaf Spot

Leaf spot is one of the most common foliar diseases found in gardens. However, it looks more like a burn than a disease; leaf spot is a fungal disease infecting plants through their leaves. Leaf spots can cause significant damage if not treated promptly.

The leaf spot appears as dark, circular blotches on leaves. They range in size from ¼ inch (0.5 cm) to several inches (1 m). Smaller spots usually appear first, but larger spots can appear later. The edges of leaf spots tend to curl inward slightly. The disease spreads quickly when temperatures rise during hot spells.

Infected areas of leaves become discolored and die off. This results in thinning or partial removal of leaves. Plants may also develop smaller, less healthy leaves. Eventually, the leaf spot kills the plant.

Foliar fungi such as Alternaria solani, Botrytis cinerea, Cercospora arachidicola, Cladosporium spp., Diplocarpon rostratum, Gaeumannomyces graminis var.

tritici, Helminthosporium teres, Leptostroma magnatum, Microdochium majus, Phoma lingam, Sclerotinia borealis, Septoria nodorum, Stemphylium spp., Thielavia subthermophila, Verticillium dahliae, and Xanthomonas campestris pv. phaseoli cause leaf spot.

5. Rust

Rust is a fungal disease that affects all types of woody plants. Most rust infections are caused by Puccinia species, a genus of hemibiotrophic fungal pathogens. Hemibiotrophs feed on living cells and then kill them using toxins and enzymes.

Rust symptoms include brown flecks on leaves and twigs or branches. An orange-yellow halo may surround these spots. If a rust fungus has infected your plant, it will show signs of wilting, premature senescence, and poor growth.

If you find any rust-like spots on your garden plant, remove them right away. Removing these spots before they spread to other plants is important until the problem is resolved; shade plants and keep them well-watered.

6. Powdery Mildew

Powdery mildew is a type of fungal disease that causes unsightly white patches on leaves and stems. It's easy to identify this condition because its effects look similar to those of powdery snow.

However, there are some differences between powdery mildew and snow. For instance, powdery mildew is often found growing on the undersides of leaves rather than on top. Also, snow melts, whereas powdery mildew remains on plant surfaces.

Powdery mildew starts with small, whitish spots on leaves. As the infection progresses, these spots grow into large patches covered with fuzzy white hairs.

In severe cases, the entire surface of affected leaves becomes covered with white fuzz. As the disease progresses, the leaves turn yellow or reddish. Eventually, the plant dies.

Powdery mildews are common on cucumbers, melons, tomatoes, peppers, eggplant, squash, and strawberries. Other susceptible plants include lettuce, onions, grapes, peaches, apples, plums, potatoes, corn, hops, and beans.

7. Whitefly

Whiteflies are tiny insects that suck the sap out of plants. Their larvae are known as aphids. Aphids have long bodies, two pairs of wings, and six legs.

Whiteflies transmit viruses and bacteria that damage plants and cause diseases. Several whitefly species are considered agricultural pests; others are beneficial pollinators. Although most people think whiteflies are harmful, their presence does not necessarily mean that your plants are under attack.

A few species of whiteflies can actually help your plants perform better. There are more than 80 different species of whiteflies worldwide. The best way to know if you're dealing with a damaging pest is to check the labels on pesticide products.

8. Downy mildew

The downy mildew affects leaves and other parts of plants that grow above ground. Most often, this type of mildew appears on young, unhealthy, or stressed plants. It thrives in cool, moist, and damp conditions.

There are several different strains of downy mildew, each with different effects on plants. For example, some plants may turn yellow or fall dormant, while other plants may not bloom.

When downy mildew appears, the best way to manage the disease is to destroy infected plants as soon as possible. Fungicides will not work on this strain of plant disease.

9. Spider Mites

Spider mites are tiny arachnid pests that inhabit many types of plants. Because they are so small, they are difficult to see without magnification.

Spider mites do considerable damage to plants because they are voracious feeders. They attract young, tender growths such as sprouts, seedlings, and tender new leaves. When spider mites infest leafy vegetables, they can stunt plant development.

Spinning spider mite webs on plants may indicate that the organisms are present but doing little harm. However, if you notice webbing on leaves, stems, or buds, you should take action to prevent further damage.

10. Thrips

Thrips are tiny insect pests that resemble flying ants. You will find them on all parts of garden plants, including leaves, stems, buds, fruit, and flowers.

The name thrip comes from the Greek word trichomes, which means hair. Thrips have three sets of mouthparts, making them excellent at sucking fluids from plants.

The worst damage caused by thrips occurs in warm weather. Thrips chew holes in leaves, causing water loss. This can kill some plants.

How can you identify a garden fungus infection?

If you think your plant has a garden fungus infection, look for the following signs:

1. Discolored or dead leaves: Fungal diseases often start as small spots on leaves. These spots can be any color, including brown, black, yellow, or white. As the disease progresses, the spots may enlarge and kill the leaves.

2. Stunted growth: A plant with a fungal infection may stop growing or produce smaller than normal leaves and flowers.

3. Spots on stems: Fungal diseases can also cause spots to form on stems. These spots may be any color but are often black or brown. The stem may also become discolored or stunted in growth.

4. Mushrooms or other fungi growing near the plant: Many fungi form visible structures called fruiting bodies that release spores into the air to infect other plants. These structures are often mushrooms but can also be molded, mildews, or rust.

5. Unusual odors: Some types of fungi emit toxic chemicals that smell like rotting fruit or garbage. These smells don't always indicate a problem, but they are a good indicator if you suspect there might be a problem.

6. Discoloration: Plant tissues react differently when exposed to certain environmental conditions. Leaves that fade or turn yellow are usually due to stress. But when these changes occur over time, they can be an early warning sign of a more serious problem.

7. Yellowing: Another symptom of a fungal infection is a change in the appearance of leaves. Greenish-yellow, pale green or reddish areas on leaves may indicate a fungal infection.

8. Stems turning brittle: Brittle stems are another common symptom of a fungal disease. The stems break easily when touched, leaving behind splinters.

9. Bark splitting: Bark cracking, peeling, or breaking off is another sign of a fungal infection. Chewing on trees, shrubs, or vines can cause it.

10. Death of flowers can occur when a plant is infected with a pathogen. In this case, the flower will wilt before opening.

11. Insects feeding on leaves: Insects such as aphids, mealy bugs, leafhoppers, and caterpillars feed on plants. They suck juices from leaves and branches and sometimes inject toxins into plants.

How can you prevent a garden fungus infection?

1. Sanitation is the key to preventing fungal infections in the garden. Be sure to clean up any fallen leaves or debris that may be harboring spores.

2. Avoid overhead watering, which can promote fungal growth. Instead, water early in the day so that the foliage has time to dry before nightfall.

3. Choose disease-resistant varieties of plants whenever possible.

4. Maintain proper plant spacing to promote good air circulation and prevent fungal diseases from spreading quickly through a crowded garden.

5. Prune away any infected plant parts and dispose of them properly to prevent the spread of disease spores.

Frequently asked questions

1. How many types of rust diseases?

Around 8,000 rust diseases have been identified, many of which are host-specific.

2. Famine in Ireland: What Was It?

The Irish potato famine was caused by a species of rust that rotted the potatoes in the ground or storage into a gooey mess.

3. Can rust fungus be dangerous to humans?

No, rust fungus is not poisonous to humans or animals.

4. What are the signs of rust infection on my plants?

The leaf will be wet for 6- 10 hours.

5. Is there anything that kills garden fungus?

Baking Soda


We have learned about the different kinds of fungi that exist in our environment. We also learned how to identify them correctly. Finally, we discussed ways of prevention and treatment of fungal blight. I hope this has helped you know and easily solve your garden's problem.

About the Author

Virginia E. Hayes is a gardening enthusiast who loves to write about gardening tools, safety issues, and ways to keep gardens clean and safe. With her vast experience in gardening, she provides valuable insights and tips to help fellow gardening enthusiasts to enhance their gardening experience. Her passion for gardening and writing has made her a sought-after author in the gardening community.

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