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5 Types of Fungal Diseases That Attack Plants

All houseplants have different needs in order to thrive. If you've ever cared for houseplants, you know that they are susceptible to common diseases that can damage and even kill them. 

Healthy indoor plants are able to resist and fight off pests and diseases as long as you're taking care of them. To keep your houseplants healthy and strong, they need certain "cultural" conditions maintained, which involves: 

  • Keeping your houseplants away from drafts
  • Not crowding them together too closely
  • Using proper soil
  • Maintaining a good balance of: light, water, temperature, humidity, and proper drainage

What Are the Common Diseases of Plants?

Almost all plant diseases (about 85 percent) are caused by fungal or fungal-like organisms. The rest are viral or bacterial, or are caused by some nutrient deficiency. Below are five of the most prominent plant diseases, common symptoms, and how to treat for them.

1. Powdery Mildew

Powdery Mildew

Powdery mildew is not a fatal plant disease, but it can make your plants look quite sickly. It's most common in outdoor plants, as it is caused by fungi spores that are blown around in the wind.

Putting your houseplants outdoors to get some fresh air and sun is obviously exposing them to powdery mildew. Putting your plants too close together or in locations that are warm and damp can also increase the chances of this fungal disease catching on and spreading to your other plants.

  • How to Tell if You Have Powdery Mildew

The first sign of powdery mildew problems usually appears as white, powdery spots or splotches on the top sides of the plant leaves, and/or on the plant stems, like the plant has been dusted with white powder. Over time the whiteness may become dull and the leaves will turn yellowish and twisted. If left untreated, the fungus will spread over the rest of the plant, including the undersides of the leaves and the flowers. 

  • How to Treat Powdery Mildew

Remove the infected leaves carefully (do not shake and spread the spores around to your other plants). You'll want to treat your affected plant(s) (around the plant base) with a product labeled to treat fungus (fungicide), like our Maggie's Farm 3-in-1 Garden Spray (insecticide, miticide, fungicide), which uses naturally derived active ingredients like thyme oil, geraniol, cinnamon oil, and peppermint oil.

2. Black Spot

Black Spot

Black spot (also "blackspot"), is a common fungal plant disease that can also be caused by certain species of Pseudomonas bacteria. Black spot primarily affects rose plants, but it can also attack other ornamental and garden plants. It affects flowers, fruits, and leaves and becomes a problem most when conditions are hot and humid. When leaves get wet and stay damp for 6 hours or more, watch out.

  • Symptoms of Black Spot

Black spot typically manifests itself as quickly expanding purple-ish to black spots on the upper surfaces of the  plant's leaves. These spots may feature yellowish halos, and may or may not cause the leaves to drop. You may also notice black lesions on younger stems.

  • How to Get Rid of Black Spots on Plants

Treat your plants around the base with a product labeled to kill fungus through the spring and summer. Remove plant debris from your garden beds in the fall to prevent black spot from overwintering in the leaves and branches that have dropped. Discard infected plant material in the trash, rather than composting it in order to contain the fungus' spread. Remember that leaves that stay damp for too long provide prime conditions for black spot, so water at the base of the plant.  

3. Leaf Spot

Leaf Spot

What is leaf spot on plants? "Leaf Spot" is a generic term used to identify many different plant diseases. Larger clusters of fungal leaf spot are referred to as anthracnose or canker, and the disease can cause leaves to turn yellow and drop prematurely. This fungal disease is a clever one and can survive and reproduce itself in dead plant debris.

  • Leaf Spot Symptoms

Leaf spot disease, simply put, appears as spots on your plants' leaves. The spots can vary in color and size, depending on the plant, on the specific fungal organism, and on where the disease is at in its development. These spots are most often a shade of brown, but may also be tan or even black, and may often feature concentric rings or dark outer margins.

  • How to Treat Leaf Spot 

Keep the plant's leaves as dry as possible, by watering them at the base instead of over the leaves. Keep your plants free of all diseased leaves and branches throughout the season and then again before winter sets in. Treat with an anti-fungal garden treatment product, paying closer attention to the plant's base.  

4. Rust


Rust is a common disease on rose plants (more so outdoors), as well as on Chrysanthemums, Fuchsias, and Pelargoniums indoors. It is also a very difficult infection to get rid of. If you suspect one or more of your plants are infected, isolate them as quickly as possible to help prevent spreading. 

  • Symptoms of Rust on Your Plants

What does rust on your plants look like? It will usually appear as rings or spots of brown on your plants' leaves, and they most often start on the leaf undersides. Eventually the spotting will be visible on both sides of the leaves. Even without yellowing first, leaves may fall prematurely if they are brushed or rustled.  

  • How to Treat Rust on Plants

Rust is a tough one to get rid of, but you might be able to keep it under control. Gently remove the infected leaves (trying not to shake and spread the fungus). Spraying a good fungicide garden spray around the base of the plant can also help greatly.

5. Blight


Generally speaking, blight is a fungal disease, and similar to powdery mildew, is spread by fungal spores blowing in the wind. Infected plants left growing in vegetable patches, or plants growing from infected plant material can be sources of the fungal infection. 

  • What Does Blight Look Like on Plants? 

Blight causes browning, and then death of plant tissue (leaves, branches, flowers). There are many diseases that cause similar symptoms in plants, and referred to as "blights."

  • How to Treat Plant Blight

Treating plants with a preventive fungicide garden spray early in the season, before symptoms start occurring, can offer some protection. Preventive treatments can also be effective in warm and moist conditions. 

5 Types of Fungal Diseases That Attract Plants infographic

What to Use to Kill Fungus on Plants

Geraniol, thyme, cinnamon, and peppermint are natural essential oils, and are all active ingredients in Maggie's Farm 3-in-1 Garden Spray. These particular essential oils are known to be very effective against fungi that infect humans as well as plants. Our 3-in-1 Garden Spray is truly a triple threat, in that it is also an effective miticide and insecticide to help protect your plants and keep them healthy.  

Maggie's Farm 3-in-1 Garden Spray kills insect pests on contact with residual repellency, and prevents and controls fungal diseases including powdery mildew, black spot, leaf spot, rust and blight. It is the perfect garden fungicide. It also effectively kills and repels the most common garden pests including ants, aphids, leaf-eating beetles boxelder bugs, caterpillars, crickets, lace bugs, leafhoppers, mealy bugs, mites, scale crawlers, stick bugs, thrips, whiteflies, and other garden pests.

Use our 3-in-1 Garden Spray for home gardening for roses, flowers, houseplants, shrubs, vegetables, herbs and other edible/consumable and ornamental plants.

We specialize in killing bugs, but we're all about keeping things "greener" and can help you keep your plants healthy and strong! For scientifically-tested, effective solutions for your home and garden that are friendly to the environment, try Maggie’s Farm pest control products. Our promise is that our plant and mineral-based products are developed by scientists and seasoned pest and fungus control professionals to be the most effective.

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