Your plant looks sick, and you don't know why. Maybe the leaves have spots. Maybe a branch has a dark, sunken patch on it. Maybe the roots have gone soft and brown, and the whole plant is wilting even though the soil is wet. Fungi cause most of these problems. This page walks through the fungal diseases you're most likely to see, sorted by the part of the plant they hit first, so you can match what you see to what's wrong.
In short:
- Fungal diseases show up in three places first: the leaves and flowers, the stems and twigs, or the roots and crown.
- Anthracnose, powdery mildew, downy mildew, and rust are the most common diseases on leaves and flowers.
- Cankers and dieback are the main signs of a stem or twig infection.
- Root rot and damping off live in wet soil and often kill a plant before you notice anything wrong above ground.
Many kinds of fungi attack ornamental plants and cause a wide range of symptoms on different plant parts:
Fungal Diseases That Attack Flowers, Fruit, Leaves And Needles
These fungi cause black spots, blights, blisters, fuzzy white or orange coatings or deformities on flowers and foliage. The usual suspects are anthracnose, powdery or downy mildews and rusts.
Anthracnose shows up as dark, sunken spots on leaves and fruit, and spreads fastest in wet, humid weather. Powdery mildew coats leaves in a white or gray powder and likes dry soil paired with humid air. Downy mildew looks similar from the top of the leaf, but flip the leaf over and you'll find a fuzzy, purple-gray growth underneath. Rust leaves small orange, yellow, or brown bumps on the underside of leaves — brush a finger across one and it leaves rust-colored dust behind.
Two more worth knowing: black spot, common on roses, forms round black spots on leaves that then turn yellow and drop off. Botrytis blight, also called gray mold, covers flowers and buds in a fuzzy gray coating after a stretch of cool, damp weather.
Fungal Diseases That Attack Stems And Twigs
Stem infecting fungi cause blight, decay, dieback, and shelf like growths on bark surfaces. Most over-winter in dead stems or twigs and produce spores in spring or early summer.
Canker fungi kill small patches of bark and the wood underneath it. You'll see a sunken, discolored patch on the stem, sometimes with cracked or oozing edges, and leaves above the canker wilt or the branch dies back. Dieback itself starts at the tip of a branch and works its way down toward the trunk, browning and curling the leaves before the whole tip dies.
Verticillium wilt is a soil fungus that clogs a plant's water-carrying tissue from the inside. Leaves on one side of the plant, or one branch at a time, wilt and turn yellow even when the soil is moist. Pruning out dead or infected stems each year keeps these fungi from spreading to new growth.
Fungal Diseases That Attack Roots And Crowns
Root-infecting fungi usually live in the soil, causing decay of plant roots and/or crowns (where the roots join the stems at soil level). Pale, wilted lower leaves signal infected roots which are swollen, and discolored. Infected plants usually die. Damping Off disease of seedlings is an example of this type of disease.
Root rot fungi, including Pythium and Phytophthora, are the main culprits. They thrive in soil that stays wet too long, turning roots brown, soft, and mushy instead of firm and white. Damping off specifically attacks seedlings right at the soil line — the stem turns thin, dark, and pinched near the base, and the seedling falls over and dies within a day or two. Both spread fastest in soil that doesn't drain well, so improving drainage does more to stop them than anything you can spray.
What Is a Fungal Disease, And How Is It Different From Other Plant Problems?
Not every yellow leaf or brown spot is caused by a fungus. Bacteria, viruses, insects, and simple stress from too much or too little water can all look similar at first glance. The biggest clue is speed. Fungal diseases usually take days or weeks to show up and spread, while bacterial and viral problems can strike fast. If you want a closer look at how to tell them apart, see Diagnosing Fungal Disease.
What To Do When You Spot One?
Once you know which fungus you're dealing with, the fix depends on where it lives and how far it's spread. Pulling off infected leaves, improving airflow, and watering at the soil line instead of overhead stop most fungal problems from spreading further. For plants that need more help, see Control Not Using Fungicides, Control With Natural Fungicides, or Control With Synthetic Fungicides for the next steps.
Common Questions About Fungal Diseases in Plants
What are the types of fungal infections in plants?
Plant fungal infections generally fall into three groups based on where they attack: foliage diseases like anthracnose, powdery mildew, downy mildew, and rust that hit leaves and flowers; stem and twig diseases like cankers and dieback; and root and crown diseases like root rot and damping off that live in the soil. Matching the symptom to the part of the plant it's on is the fastest way to narrow down which fungus you're dealing with.
How do I know if my plant has a fungal disease?
Look for spots, powder, or fuzzy growth on the leaves, sunken or discolored patches on the stems, or roots that have turned soft and brown instead of firm and white. Fungal problems also tend to build up slowly, over days or weeks, instead of overnight.
How do I know if my plant has a fungal or bacterial infection?
Speed is the biggest clue. Fungal diseases usually take days or weeks to cause visible damage, while bacterial infections can wilt or blacken a plant within a day or two. Bacterial spots also tend to look wet and greasy, while fungal spots are usually dry and clearly outlined.
Can a plant recover from a fungal infection?
Yes, if you catch it early. Removing infected leaves or stems, improving airflow, and fixing the watering habit that let the fungus take hold in the first place give a plant a real chance to grow out of it. Root and crown infections are harder to recover from, since the damage happens underground before you see any warning above it.
CONCLUSION
Most fungal diseases give themselves away once you know where to look. Check the leaves and flowers first, then the stems, then dig a little at the base of the plant if the top still doesn't explain what you're seeing. Catching the problem early, and fixing the conditions that let it take hold in the first place, whether that's crowded plants, wet leaves, or soggy soil, stops most fungal diseases before they do real damage.
