Fungal, Viral, or Bacterial? Types of Plant Diseases
When you hear the word "disease", you likely think of a human condition. However, your plants are living, even breathing organisms who can also contract diseases, whether its fungal, viral, or bacterial.
Around 85% of plant diseases are caused by fungal or fungal-like organisms, but viral and bacterial organisms can also caused problems in your garden too. Left untreated, these infections can spread quickly, leaving your once-thriving plants wilted, spotted, or stunted.
Recognizing the type of disease is the first step to saving your plants. Let's break down the most common plant diseases, how to identify them, and what you can do to prevent or treat them.
Types of Plant Diseases
Not all plant diseases are created equal. The way a disease spreads, the symptoms it causes, and how you treat it often depends on whether it’s fungal, viral, or bacterial.
Fungal Plant Diseases
Fungal diseases are by far the most common, accounting for the majority of garden problems. They're caused by fungi or fungus-like organisms that thrive in damp, humid conditions. These diseases often spread through spores, which can travel by wind, rain or even dirty gardening tools.
What to look for:
Leaf spots or blights
Powdery mildew (a white, dusty coating)
Rust-colored spots or pustules
Wilting, root rot, or mold on the soil surface
Common examples: Powdery mildew, rust, damping off, and leaf spot diseases.
How to handle it:
Improve air circulation, avoid overhead watering, and treat with fungicides if necessary. Always remove and dispose of infected plant material.
Viral Plant Diseases
Viruses are a little trickier. Unlike fungal infections, viral diseases often produce more subtle symptoms, making it harder to diagnose them, and there's no cure once a plant is infected. These diseases often spread by insects like aphids or whiteflies, or through infected pruning tools.
What to look for:
Yellow mottling or streaking on leaves
Distorted or curled leaves
Stunted growth
Unusual patterns or “mosaic” discoloration
Common examples: Mosaic virus, tomato spotted wilt virus, and cucumber mosaic virus.
How to handle it:
Remove and destroy infected plants to prevent spread. Keep pests under control, sterilize tools, and avoid using infected seeds or starts.
Bacterial Plant Diseases
Bacterial infections are less common but can still do serious damage. They often enter through wounds in the plant or natural openings and can spread quickly in warm, wet conditions.
What to look for:
Water-soaked spots that turn brown or black
Oozing lesions or slime
Wilting despite moist soil
Leaf spots with yellow halos
Common examples: Bacterial wilt, fire blight, and bacterial leaf spot.
How to handle it:
Remove infected plant parts, improve drainage, and avoid overhead watering. Copper-based sprays can help in some cases, but preventing it is key.
How to Prevent and Treat Plant Disease
Even the healthiest garden can suffer from a plant disease - just like even the healthiest of humans can still get sick. But most plant diseases can be prevented, or at least managed, if you know what to look for and what to do.
Start With Prevention
It may seem obvious, but the best way to prevent plant disease is to stop it before it starts. Prevention is all about creating the right environment for your plants, and the wrong one for disease.
Choose disease resistant plants: Many seed packets or plant tags will tell you if a variety is bred to resist common diseases. Look for these.
Give your plants some space: If your plants are crowded, they tend to trap moisture and limit airflow, which is the perfect breeding ground for fungi and bacteria. A general guideline is to space plants about 12-18 inches apart, but larger plants like sunflowers or vining crops may need around 48-60 inches.
Water the right way: Remember to water the soil and not the leaves. It's also good to water earlier in the day, so the moisture has enough time to evaporate.
Rotate your crops: If you plant the same thing in the same spot every year, it can build up soil-borne diseases.
Clean your garden tools: Dirty garden tools can spread viruses and bacteria from plant to plant.
Remove debris: Dead leaves and plant matter can harbor pathogens, so it's important to keep your garden tidy.
Common Treatment
If your plant does develop a disease, don't panic. There are ways you can help stop the disease from spreading.
Act fast: As soon as you start to see signs of trouble, remove the affected plants or leaves.
Use natural or chemical treatments:
For fungal, use a fungicide (like copper or sulfur-based sprays).
For bacterial, copper sprays may help but aren’t always effective.
For viral, unfortunately, there is no cure. Remove and destroy the plant.
Quarantine your plants: Keep the diseased plants separate from the healthy ones to prevent cross-contamination.
Improve your plant's home: More airflow, better drainage, or a change in sunlight can all help your plants recover and stop the disease from spreading.