Fungus is a surprise we never like getting. It always seems to me that one day my plants are just fine.  Then next…ewww…there’s stuff on my once pristine leaves and they’re turning yellow or brown.

Fungus spreads by spores that float through the air or that are transferred by insects or dirty pruning shears. They also spread by their “roots”, referred to as mycelium. By the time you see the true signs of fungus, it’s because their “fruiting bodies” are releasing said spores.

Let’s take a closer look at some common Florida fungus problems, and of course I wouldn’t leave you hanging, we’ll look at fixes too.  Momma always said to come to her with a solution, not a problem, unless you have absolutely exhausted all resources of finding the answer yourself and don’t know where else to look.  (It’s no wonder I ended up doing cancer research towards the end of my first Bachelors’ degree and still love research now!)

Mycelium of fungus

Plant Fungus: What is it?

Plant Fungus is very much like any other fungus. They feed on the organism(s) they live on or near, and when the food is gone – or is so plentiful that they need help consuming it –  they fruit, release spores, and start the cycle over again.

Fungi on the surface of plants usually causes leaves to become dessicated, spotted, turn brown and fall off.  Remember that fungi are the world’s “rotters” and are responsible for the majority of decomposition for all things that (eventually) die.  Some fungi are more aggressive and cause the death of the organism which it is consuming, and those are the ones we’re talking about today in the plant world.

Fungus examples on plants

Why are fungus on my plants?

Sadly, we can’t say they have an agenda except this: Fungi Must Survive.  It’s survival of the fittest in all the organism kingdoms, and fungi are no exception.

Fungi are born hungry. Their whole lives are about eating so they can reproduce and make more hungry fungi.  This is a good thing for an organism responsible for decomposition – if they didn’t exist there would be no way we could have the world we have now. 

Imagine if NOTHING decomposed?  Dinosaurs dropped dead, and just stayed there, whole and huge? Massive piles of dead things everywhere?  Imagine forests where dead leaves, branches, and trees never rotted away to make it possible for new growth?

Now you know how important they are overall. And you know how hungry they are.  Now let’s talk about what they look like on your plants so that you can see them and know they’re there.

What do Fungi look like on my garden plants?

Fungi come in many shapes and colors, and show up in different ways in your garden.  Let’s explore some really common ones!

Fungus A: Black Spot

black spot fungi on rose leaves

Black spot is the bane of all rose-grower’s existence here in Florida.  A very common and prolific fungus, it shows up as black spots on the beautifully serrated leaves of your roses.

One or two spots won’t take out your rose bush, but eventually it will spread to all the leaves.  The leaves become mostly covered in the black spots, and the leaves can no longer survive.  They turn yellow, then eventually fall off.

A large infestation of black spot can compromise your overall rose bush, making it impossible for it to flower or produce new leaves, because there aren’t enough unaffected leaves to perform photosynthesis. If unchecked, black spot will contribute heavily to the death of your rosebush.

Here’s an article from Clemson University about Rose Diseases if you’re interested in learning more. 

Fungus B: Powdery Mildew

powdery mildew fungus on curcubit leaf

Powdery mildew is something most seen on the leaves of the Curcubit family, as those plants are the most susceptible to it.  The Curcubit family includes squashes, cucumbers, and melons.

This fungus starts as what looks like a really light dusting of powder, and over time grows so thick that it blocks the leaves’ ability to breathe and photosynthesize.  The leaf succumbs to starvation and dies.

If not controlled, powdery mildew will continue to attack leaves, keeping the plant from producing fruit due to a lack of energy production.

More information about Powdery Mildew from an extension office can be found here. 

Fungus C: Downy Mildew

Downy mildew lesion on the bottom of a leaf

I like to think of Downy Mildew as the shy cousin of Powdery mildew.  Where powdery mildew is flambuoyant and very showy, downy mildew stays in the shadows, hidden.  And yet they’re both just as deadly to your plant!

Downy mildew forms colonies on the underside of leaves, that range from white to black on the underside.  On the top of the leaf, you’ll see brown patches corresponding to the downy colonies on the underside.  

The downy patches will grow in size until the whole leaf is brown.

Here is more information from an Extension office about Downy Mildew. 

Fungus D: Botrytis

The Many Faces of Botrytis Grey Mold

Botrytis affects many of our edible crops and also flowering plants.  It is a very common and very indiscriminate mold that just loves our favorite vegetables, such as strawberries and tomatoes and blueberries, and also plants like begonias and other ornamentals.

I made a collage of images because Botrytis can look like many different things – a kind of chameleon if you will!  On fruit, early on, it will appear as brown spots that are pretty “mushy”.  On leaves, it will show up as brown spots on top with fuzzy grey/black mold on the underside (remember, downy mildew can look that that too!)

In advanced stages, you’ll sometimes see these little hairs with “dots” on the end standing up from the surface.  Other times you’ll just see a grey, watery, mushy mess where a flower or a fruit might have been.

Learn more about Botrytis with this article from an Extension office. 

Fungus E: Southern Blight

The many faces of southern blight

Southern Blight is a very aggressive fungus which affects many different vegetable crops and ornamentals, turf, and even some trees!

There is a characteristic circular growth pattern in a large infestation like in grass or in a field crop or large flower bed.  On individual plants, one of the most easily recognized signs is a “spiderweb” of white fungal mycelium extending down and out of the infected area, which is how the fungus spreads.

Mycelium are like “roots” in a plant – it’s how the fungus interacts with its surroundings and gathers nutrients, and also spreads itself over large areas.

Want to know more about Southern blight? Click for an extension office article.

In the images above, clockwise, blight is affecting a portion of the ornamental bush (top left). White mycelium grow from an infected Peanut stem down into the soil (top right). Southern Blight in turf grass, note the circular pattern and the bright white edge where the mycelium are spreading into further territory (bottom right). Infected pepper plants have soggy stems at the base where the fungus is spreading into the soil, and peppers suffer from fungal rot and also sunscald due to weakened fruit (bottom left).

Fungus F: Rust

Rust fungus on different plants

Rust fungus has a cheerful orange “pustule” that makes it very easy to see.  It can affect many different kinds of plants, both food crops and flowers. In Florida you’ll often see it on ornamenals such as roses and plumeria/frangipani, where it causes premature leaf drop.

For the most part, Rust fungus rarely causes overall plant damage or death, unless the plant is infected with other disease(s).  It does discolor the leaves and sometimes flowers/fruits of your plants, and for that reason alone most people choose to treat it.

Here’s more information about Rust.

OK, I Know What To Look For, Now What Do I Do About Fungus?

fungicide application

Preventative Measures

The best Defense is a good Offense, right?  Here’s some things that you can do to help steer clear of fungus problems in the garden.

1) Trim up leaves close to the ground. This helps the surface soil or mulch dry between waterings. Standing water is the perfect host for fungus!

2) Water at the soil level only. Keeping leaves dry by watering the soil only is a great way to help keep fungus from beginning.

3) Water in the mornings only. Allowing leaves and fruit to be sun dried after your irrigation helps keep fungus at bay.

4) Practice proper plant spacing and pruning. All plants need clean air flow for optimal health. Prune to ensure air can circulate around your plant effectively, and follow spacing instructions when you plant.  If something is getting too big for its space, find it a new home!

Go On Attack Mode

The threat has already made itself known, and it’s just so hot and wet outside all the time.  What do you do then? Here’s some tips:

1) Apply fungicides. The obvious answer is usually the best (a derivative of Occam’s Razor, for you folks appreciating philosophy out there). Fungicides are made to help you win Battle Fungus.  There are many kinds out there, but a few of my favorites are the Garden Friendly Fungicide by Southern Ag (an organic option), Liquid Copper Fungicide by Southern Ag, and any of the forms of Daconil out there.  They all work great when applied properly.  My biggest application tip: consistency throughout the season AND make sure you get the bottoms of the leaves!!!

2) Remove affected leaves quickly. You may be able to stop the spread by inspecting and removing affected parts of the plant as soon as you see a problem. Make sure you clean your blades between cuttings with rubbing alcohol to keep from spreading the fungus.

3) Don’t compost infected plants. The fungus will live in your compost, then you spread it to your other plants when you use the compost.  I suggest burning them.  You can then use the ash to till into the soil at a future date to increase your carbon availability in the soil.

4) Use Azomite when you fertilize. Azomite is like an immune booster, but for plants. It has micronutrients that can help keep plants healthy, and it doesn’t have nitrogen or phosphorus that will leach into ground waters or marine waters to cause red tide.


Would I be hurting the good fungus in the soil with fungicides?

In short, the answer is Yes, but only temporarily. 

Fungus has this amazing ability to spread very quickly.  All fungus share this trait (for the most part, I’m sure there are exceptions!), and so, in the name of preserving your food or flower crops, your ornamentals, etc., the minor damage you’d do to the good fungi like mushrooms and such will not be noticed to much by Mother Nature, when used sparingly and when necessary.

There is, of course, the possibility of applying too much, like we see in areas of monoculture plants like lawns and such, where all fungal life is wiped out and the soil becomes stripped of nutrients and inhospitable to plant life in general.  There must be a balance in the application of any chemicals to the Earth, and only you can make the decision of what is enough for your needs.


I really hope this article was helpful to you!  Let me know what else you want to learn about! 

Until next time, Keep Growing!



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