Leaf Spot & Brown Spots on Leaves: How to Identify, Treat & Prevent Them

Found brown spots on your leaves and wondering whether your plant is sick?

Don’t reach for the spray bottle just yet.

Brown, black or yellowing spots can be caused by leaf spot disease, but fungal and bacterial infections are only part of the story. Overwatering, wet foliage, heat, fertiliser problems, pests and even spray damage can produce surprisingly similar symptoms.

The trick is working out what the spots are telling you before you treat them.

In this guide, we’ll show you how to identify the most common causes of leaf spots in Australian gardens, how to tell fungal leaf spot from bacterial leaf spot, what to do with affected leaves, when treatment is actually necessary and how to reduce the chances of the problem returning.

Table of Contents

• Brown Spots on Leaves? Check These 5 Things First
• What Is Leaf Spot?
• What Causes Brown Spots on Plant Leaves?
• Quick Leaf Spot Identification Guide
• Fungal vs Bacterial Leaf Spot: How Can You Tell?
• Common Leaf Spot Diseases in Australian Gardens
• How to Treat Leaf Spot
• How to Use Lime Sulphur Safely
• Should You Cut Off Leaves With Brown Spots?
• Can a Plant Recover From Leaf Spot?
• When Leaf Spot Is Serious — And When It Isn't
• How to Prevent Leaf Spot From Coming Back
• Brown Spots on Tomato Leaves
• Brown Spots on Rose Leaves
• Brown Spots on Indoor Plant Leaves
• Leaf Spot After Rain
• The Biggest Leaf Spot Treatment Mistakes
• Frequently Asked Questions About Leaf Spot
• A Simple Leaf Spot Action Plan
• Final Thoughts
• Next Reads for Diagnosing Spots and Plant Disease Properly

Not sure what’s causing the spots yet? These are the tools that make inspection and treatment easier once you’ve identified the likely cause:

Brown Spots on Leaves? Check These 5 Things First

Before diagnosing leaf spot disease, have a close look at the plant.

Ask yourself:

1. Are the spots dry and crispy or soft and water-soaked?
2. Is there a yellow, purple or dark border around each spot?
3. Did the problem begin on older lower leaves or new growth?
4. Has the weather recently been wet, humid or unusually hot?
5. Can you see insects, webbing, scale or feeding damage underneath the leaves?

These little clues can quickly separate a genuine plant disease from environmental stress.

A brown mark by itself doesn't automatically mean fungus.

What Is Leaf Spot?

Leaf spot is a broad term used for visible areas of damaged or dead tissue that develop on leaves.

Depending on the cause, those spots may be:

• Brown
• Black
• Grey
• Tan
• Yellow
• Reddish or purple-edged
• Circular
• Angular
• Irregular
• Dry and papery
• Soft or water-soaked

Some leaf spots stay tiny. Others enlarge, merge together and eventually kill large sections of the leaf.

The important bit is that leaf spot isn't always one single disease.

Many different fungi and bacteria can produce leaf spots, and similar markings can also come from watering problems, heat, nutrient issues, chemical damage and pests.

That’s why identifying the pattern matters.

What Causes Brown Spots on Plant Leaves?

Here are the most common possibilities.

1. Fungal Leaf Spot

Fungal leaf spot is one of the most common causes of spotted foliage.

Fungal diseases generally become more troublesome when leaves remain wet for long periods, air circulation is poor or spores are continually splashed from infected leaves and garden debris onto clean growth.

Depending on the organism involved, fungal leaf spots may appear as:

• Round brown lesions
• Tan or grey centres
• Dark borders
• Yellow halos
• Concentric rings
• Tiny black dots inside older spots
• Spots that enlarge during wet weather

Some fungi are highly plant-specific, while others affect a wider range of ornamentals, vegetables and fruiting plants.

2. Bacterial Leaf Spot

Bacterial leaf spot can look frustratingly similar to fungal disease.

Early lesions may look dark, greasy or water-soaked before becoming brown or black. On some plants the spots are more angular because the damaged tissue is restricted by the leaf veins.

Bacteria are easily moved by splashing water, contaminated tools and handling wet plants.

That makes sanitation particularly important.

3. Overwatering and Constantly Wet Foliage

Too much water doesn't just affect roots.

Regular overhead watering, dense foliage and constantly damp leaves create conditions where many plant diseases can establish more easily.

If you’re watering every day “just to be safe”, check the soil first.

Our guide to correctly watering your garden explains how to water deeply while keeping foliage drier and reducing unnecessary disease pressure.

4. Underwatering, Heat and Leaf Scorch

Not every brown spot is infectious.

Severe heat, dry winds and irregular watering can cause:

• Crispy leaf tips
• Brown margins
• Scorched patches
• Papery sections between veins
• Sudden damage on the sun-facing side of a plant

This is especially common in pots, where root zones can dry out surprisingly quickly during an Aussie summer.

If the damaged tissue is dry, sharply scorched and isn't continuing to spread from leaf to leaf, environmental stress deserves a closer look before you assume disease.

5. Nutrient Problems

Certain nutrient deficiencies or imbalances can cause brown spotting, yellowing and damaged leaf margins.

Calcium issues, for example, can contribute to brown speckling and damage on developing growth, while other nutrient problems may produce yellowing between veins or progressive leaf-edge damage.

If spots are accompanied by unusual colour changes rather than obvious lesions, read our guide to spotting and fixing plant nutrient deficiencies before treating for disease.

6. Pest Damage

Spider mites, thrips, scale and other sap-sucking pests can produce stippling, bronze areas, scarring and spots that are easily mistaken for disease.

Always flip the leaf over.

Check for:

• Tiny moving insects
• Fine webbing
• Sticky residue
• Raised scale-like bumps
• Black specks
• Silvery feeding scars

If you can't see enough with the naked eye, magnification can make diagnosis much easier.

7. Spray or Fertiliser Burn

A foliar spray applied too strongly, in harsh sunlight or to a sensitive plant can damage leaves.

Likewise, excessive fertiliser salts may contribute to burned margins and stressed roots.

If the spotting appeared suddenly after spraying or feeding, consider that timing before blaming a pathogen.

Quick Leaf Spot Identification Guide

This table is a starting point, not a laboratory diagnosis.

Different plant diseases can look very similar. If a valuable plant is deteriorating quickly, the safest approach is to identify the host plant, environmental conditions and full symptom pattern rather than relying on one spot alone.

Fungal vs Bacterial Leaf Spot: How Can You Tell?

This is one of the trickiest parts of leaf diagnosis.

There is no single visual rule that separates every fungal disease from every bacterial disease, but there are useful clues.

Fungal leaf spot may show:

• Circular lesions
• Dry centres
• Distinct borders
• Concentric rings
• Tiny dark fungal structures
• Increasing symptoms during humid or wet weather

Bacterial leaf spot may show:

• Wet or greasy-looking early lesions
• Angular spots limited by veins
• Yellow halos
• Rapid spread after rain or overhead watering
• Damage that expands into larger dead areas

The overlap is significant.

So rather than asking only “What colour is the spot?”, consider:

What plant is affected + where the spots started + recent weather + whether leaves have stayed wet + how quickly the problem is spreading.

That combination gives you a much better diagnosis.

Common Leaf Spot Diseases in Australian Gardens

Septoria Leaf Spot

Septoria diseases can produce numerous small spots, often with pale or greyish centres and darker edges.

Tomatoes are a well-known host of Septoria leaf spot, where symptoms commonly begin on lower foliage before moving upwards when conditions favour disease.

Removing heavily infected lower foliage and reducing water splash can help slow the spread.

Cercospora Leaf Spot

Cercospora leaf spot occurs on a wide range of plants.

Depending on the host, symptoms may begin as small brown flecks that develop lighter grey centres and darker red-brown or purple margins.

In some cases the dead centre of the lesion eventually drops away, leaving a shot-hole appearance.

Warm, wet weather can favour disease development and spread.

Alternaria-Type Leaf Spots

Alternaria diseases often create distinctive brown lesions, sometimes with darker concentric rings that resemble a target.

They may become more noticeable on older foliage, especially when plants are already stressed.

Bacterial Leaf Spot

Bacterial leaf spot isn't one single organism.

Different bacteria can infect different host plants, producing lesions that range from small dark specks to larger water-soaked or angular patches.

Reducing splash, avoiding unnecessary handling of wet plants and cleaning tools between affected plants are particularly worthwhile precautions.

Black Spot

Black spot is especially familiar to rose growers.

Dark lesions are often accompanied by yellowing foliage and premature leaf drop.

For gardeners also dealing with powdery white fungal growth rather than spotting, see our guide on how to get rid of powdery mildew.

How to Treat Leaf Spot

A good leaf spot treatment strategy doesn't begin with blindly spraying everything in sight.

Start by breaking the conditions that allowed the problem to spread.

Step 1: Remove the Worst Affected Leaves

If only a handful of leaves are heavily spotted, remove the worst ones with clean secateurs.

Don't strip the entire plant bare.

Healthy leaves are still producing energy, and aggressive pruning can add even more stress.

Bag badly diseased material rather than dragging it around the garden.

Step 2: Clean Up Around the Plant

Dead and infected leaves sitting underneath the canopy may provide a continuing source of disease material.

Remove fallen foliage and keep the area around susceptible plants reasonably clean.

Step 3: Stop Wetting the Leaves

Water the root zone whenever practical.

Constant overhead irrigation can spread spores and bacteria through splash while also leaving leaves wet for longer.

Morning watering is generally preferable because any accidentally wetted foliage has more opportunity to dry through the day.

For a full watering strategy, read How to Correctly Water Your Garden.

Step 4: Improve Airflow

Dense, crowded plants stay damp longer.

Where appropriate:

• Thin congested growth
• Give plants adequate spacing
• Remove heavily crowded interior foliage
• Keep weeds under control
• Avoid packing pots tightly together

The goal isn't to expose everything to harsh sun.

It's simply to help moisture evaporate rather than sitting on foliage for hours.

Step 5: Clean Your Tools

If you've been pruning affected plants, clean secateurs before moving to healthy specimens.

This is particularly important when bacterial disease is suspected.

Step 6: Decide Whether a Fungicide Is Actually Appropriate

If the problem genuinely appears to be fungal, a labelled fungicide may form part of the management plan.

For applicable fungal problems such as black spot, rust and powdery mildew, Kendon Lime Sulphur is one option available from Dr Greenthumbs.

Lime sulphur is a contact treatment, so good coverage matters. Always use the product strictly according to its label, check that your particular plant and problem are suitable for treatment and patch-test sensitive plants where appropriate.

Do not assume that one fungicide treats every cause of brown leaves.

Bacterial disease, heat scorch, nutrient problems and pest damage require different responses.

You can also browse our wider pest control and plant protection range when you've identified the actual problem.

How to Use Lime Sulphur Safely

Lime sulphur can be useful for appropriate labelled problems, but more isn't better.

A few practical rules:

• Follow label dilution rates exactly.
• Spray in mild, dry conditions.
• Avoid harsh midday sun and extreme heat.
• Don't spray when rain is imminent.
• Thorough coverage matters because it works by contact.
• Avoid spraying active pollinators.
• Keep children and pets away during application and until treated areas are dry.
• Be cautious with tender seedlings and soft new growth.
• Don't casually mix it with horticultural oils, copper products or other garden chemicals.
• Rinse spraying equipment after use because sulphur products may be corrosive to some materials.

If you're unsure whether lime sulphur is suitable for the plant in front of you, check the label first rather than guessing.

Should You Cut Off Leaves With Brown Spots?

Usually, remove leaves that are badly diseased, mostly dead or clearly contributing to ongoing spread.

But don't automatically remove every leaf containing a tiny blemish.

If 80% of the canopy has a few spots and you remove 80% of the foliage, you've created a new problem.

Plants need functioning leaves to photosynthesise and recover.

A sensible approach is:

A few heavily affected leaves: remove them.

Minor isolated spots: monitor them.

Rapidly increasing spots: investigate and act.

Most of the plant affected: focus on diagnosis and overall plant health rather than panic-pruning.

Can a Plant Recover From Leaf Spot?

Absolutely — in many cases.

A spotted leaf usually won't become perfectly green again because dead tissue stays dead.

What you're looking for is healthy new growth and no continuing spread.

Good signs include:

• New leaves emerging clean
• Existing spots no longer enlarging
• No rapid yellowing or leaf drop
• The plant maintaining normal growth
• Fewer symptoms after watering and airflow are corrected

Don't judge treatment success by whether old brown spots disappear.

Judge it by what happens next.

When Leaf Spot Is Serious — And When It Isn't

A few marks on an otherwise vigorous mature plant may be mostly cosmetic.

Pay more attention when:

• Spots are multiplying rapidly
• New growth is being affected
• Leaves are dropping in large numbers
• Seedlings or young plants are involved
• Stems or fruit are developing lesions
• The plant repeatedly suffers severe outbreaks
• Several nearby plants are becoming affected
• The plant is losing enough foliage to weaken overall growth

That's when identification and intervention become more important.

How to Prevent Leaf Spot From Coming Back

Prevention is usually easier than repeatedly treating established disease.

Water the Roots, Not the Canopy

Keep leaves dry whenever practical and avoid creating a nightly fungal sauna.

Water Earlier in the Day

Morning watering gives wet foliage time to dry.

Improve Air Circulation

Give leaves breathing room.

This is particularly important in tightly planted veggie beds, rose gardens, indoor grow spaces and grouped container plants.

Remove Diseased Plant Material

Don't leave heavily affected foliage sitting underneath the plant.

Avoid Handling Wet Plants

Wet foliage makes it easier to move some pathogens from plant to plant.

Clean Gardening Tools

Especially when you've been cutting obviously infected tissue.

Keep Plants Healthy — Without Overdoing It

A chronically stressed plant is rarely at its best.

Healthy roots, sensible watering and balanced nutrition help plants tolerate environmental pressure much better than a boom-and-bust feeding routine.

For gardeners building healthier root systems and living soil, our guide to mycorrhizal fungi in Australian gardens explains how beneficial root fungi support nutrient and water uptake.

Just remember:

Beneficial mycorrhizal fungi and pathogenic leaf-spot fungi are completely different things.

The word “fungus” doesn't automatically mean bad news.

Brown Spots on Tomato Leaves

Tomatoes can develop brown spotting from several different causes, including fungal diseases, bacterial problems, nutrient stress, mites and environmental damage.

If lower leaves develop numerous small brown spots during warm or damp conditions, a fungal leaf spot such as Septoria deserves consideration.

If lesions are larger and display target-like rings, an Alternaria-type disease may be more likely.

Whatever the exact cause, early action helps:

• Remove badly infected lower foliage
• Keep leaves dry
• Reduce soil splash
• Improve airflow
• Don't work through wet plants
• Monitor fresh growth closely

Brown Spots on Rose Leaves

Roses are particularly prone to foliar fungal problems.

Dark spotting followed by yellow leaves and premature defoliation is a classic warning sign.

Remove badly affected foliage, clear fallen leaves and improve airflow through dense plants.

Where the diagnosed problem and product label align, Kendon Lime Sulphur is designed for fungal issues including black spot, rust and powdery mildew on suitable plants.

Brown Spots on Indoor Plant Leaves

Indoor plants add another layer of complexity because brown marks are frequently caused by care conditions rather than infectious disease.

Check for:

• Overwatering
• Poor drainage
• Water sitting on leaves
• Cold draughts
• Direct sun scorch
• Fertiliser salts
• Spider mites or thrips
• Low airflow

Don't automatically spray an indoor plant because you see a brown patch.

First work out whether the damage is actually spreading.

Leaf Spot After Rain

An outbreak appearing after extended rain doesn't automatically prove fungal disease, but wet conditions are an important clue.

Rain can:

• Keep foliage wet for long periods
• Splash spores between leaves
• Spread bacteria
• Increase humidity inside dense canopies
• Splash contaminated soil onto lower foliage

After prolonged wet weather:

1. Let plants dry where possible.
2. Remove badly infected foliage.
3. Clear debris.
4. Improve airflow.
5. Avoid additional overhead watering.
6. Watch new growth for further symptoms.

The Biggest Leaf Spot Treatment Mistakes

Mistake 1: Assuming Every Brown Spot Is Fungus

It isn't.

Diagnose first.

Mistake 2: Spraying Without Fixing the Environment

If leaves stay wet every night, spraying alone may not solve the underlying problem.

Mistake 3: Treating Bacterial and Fungal Disease as the Same Thing

They're not interchangeable.

A product intended for particular fungal diseases should not automatically be expected to control bacterial problems.

Mistake 4: Removing Too Many Leaves

Over-pruning an already stressed plant can slow its recovery.

Mistake 5: Expecting Old Spots to Turn Green Again

Damaged tissue doesn't magically repair itself.

Focus on preventing new spots.

Mistake 6: Applying Treatments in Harsh Conditions

Heat, direct sun and incorrect dilution can cause additional foliage damage.

Always follow the label.

Frequently Asked Questions About Leaf Spot

Why are there brown spots on my plant leaves?

Brown spots on leaves can be caused by fungal or bacterial leaf spot diseases, but watering problems, heat damage, fertiliser burn, pests and other environmental stresses can produce similar symptoms. Check the spot's shape, texture, border, position on the plant and whether it is spreading before choosing a treatment.

Is leaf spot contagious?

Some fungal and bacterial leaf spot diseases can spread between susceptible plants through splashing water, contaminated plant material, tools and other pathways.

Environmental damage such as sunburn or nutrient stress isn't contagious.

What kills leaf spot fungus?

There is no single treatment for every fungal leaf spot.

Management usually involves removing heavily infected material, reducing leaf wetness, improving airflow and, where appropriate, using a fungicide labelled for the identified plant and disease.

What is the best fungal leaf spot treatment?

The best treatment depends on the pathogen and host plant.

Start with sanitation and environmental control. If a fungicide is required, choose one that is specifically labelled for your plant and the disease you're treating rather than selecting a product simply because it says “fungicide”.

Can I spray lime sulphur for leaf spot?

Lime sulphur is used for several fungal plant problems, including diseases such as black spot, rust and powdery mildew, but suitability depends on the plant, disease and product label.

Check the diagnosis and label before using it.

You can view Kendon Lime Sulphur here.

Should I remove all leaves with leaf spot?

No.

Remove heavily affected or mostly dead leaves where appropriate, but avoid stripping a plant of healthy functioning foliage simply because it has a few minor marks.

Can leaf spot spread through watering?

Water splash can help move spores and bacteria from affected tissue onto healthy leaves.

Watering at soil level and allowing leaves to dry quickly can reduce this pathway.

Will leaf spot go away by itself?

Minor outbreaks may stop progressing once weather or growing conditions change.

Existing spots generally remain visible. What matters is whether new spots continue to appear.

How do I prevent fungal leaf spot naturally?

Start with the environment:

• Keep foliage as dry as practical
• Water in the morning
• Improve airflow
• Remove heavily infected material
• Clean tools
• Avoid overcrowding
• Keep plants appropriately watered and nourished

These steps reduce disease pressure without treating every plant unnecessarily.

A Simple Leaf Spot Action Plan

If you've just noticed spots today, here's the short version:

1. Don't panic.
A brown spot doesn't automatically mean a serious disease.

2. Inspect both sides of the leaf.
Look for insects, webbing and unusual lesions.

3. Check your watering and recent weather.
Wet leaves, humidity, heat and inconsistent moisture all matter.

4. Remove only the worst affected foliage.

5. Keep leaves dry and improve airflow.

6. Work out whether you're dealing with fungus, bacteria, pests or environmental damage.

7. Treat only after identifying the likely problem.

When a suitable fungal treatment is required, explore our plant pest and disease control range, including Kendon Lime Sulphur for compatible labelled uses.

Final Thoughts

Brown spots are your plant's way of telling you that something has changed.

Sometimes that's fungal leaf spot.

Sometimes it's bacterial.

Sometimes the poor thing has simply been cooked, drowned, starved, overfed or munched on.

The best gardeners don't reach for the strongest treatment first.

They look for clues.

Check the plant. Check the underside of the leaves. Check the soil. Think about the weather. Look at whether the problem is spreading.

Once you know what you're actually dealing with, leaf spot becomes a whole lot easier to manage — and you'll have a much better chance of keeping the rest of your garden healthy too.

Next Reads for Diagnosing Spots and Plant Disease Properly

Still unsure whether those marks are fungal, environmental or pest-related? These guides will help you narrow down the cause and choose the right next step.

• How to Get Rid of Powdery Mildew in Australia
• Best Organic Fungicide Australia Guide
• How to Correctly Water Your Garden
• Plant Nutrient Deficiency Guide

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