My houseplants are an important part of my indoor decor, providing texture, color, and life to almost every room in my home.
In spite of my careful ministrations – providing the right amount of water, some careful pruning when needed, and appropriate lighting – once in a while a houseplant comes down with a disease and I need to go into rescue mode.
If you grow houseplants long enough, it’s likely something you’ll experience, too – perhaps you already have, and that’s why you’re here.
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I think the hardest part of managing plant disease is figuring out what the heck you’re dealing with in the first place.
When you know what disease is affecting your houseplant, you can formulate a plan to manage it. In some cases this might be pretty simple and in others an extreme challenge.
This guide is going to go over 11 common and not-so-common problems that can infect the plants that we generally like to grow in our homes. I’ll also provide treatment options where possible.
Here are the baddies we’ll talk about:
We are going to focus purely on diseases in this guide, but it’s important to note that there are also some environmental disorders that can cause disease-like symptoms.
Brown leaf margins and tips on some species can be caused by fluoride, chlorine, or other chemicals in the water. Dry, hot air is another common cause of discolored foliage.
Too much or too little water, pest infestations, and inappropriate temperatures can also contribute to brown or yellow leaves.
Wilting foliage is often a result of over- or underwatering, and leaf drop can happen if the environmental conditions change suddenly – such as moving your houseplant into more or less light.
Here are some diseases that can afflict many common houseplant species:
1. Anthracnose
Anthracnose is the broad term for a variety of diseases caused by fungi in the Colletotrichum and Gloeosporium genera. These pathogens attack hundreds of different houseplant species, both indoors and out.
The symptoms depend entirely on the species affected. On Dracaena and Dieffenbachia species, for example, the disease causes circular lesions on the leaves and stems.
Anthracnose on orchids typically causes the leaves to turn brown and yellow before dying off.
When the disease shows up, the best way to treat it is with a biological fungicide that contains Bacillus subtilis.
This beneficial bacteria will outcompete the bad pathogens, disrupting their reproductive cycle so they can’t proliferate.
Arbico Organics carries a product called CEASE that contains this powerful bacteria in gallon and two-and-a-half-gallon containers.
CEASE Biofungicide
Follow the manufacturer’s directions for treating houseplants, and apply once a week until symptoms stop advancing.
2. Bacterial Leaf Spot
Spots on houseplant leaves can be caused by fungi or bacteria. When bacteria is the culprit, it’s a pathogen in the Erwinia, Pseudomonas, or Xanthomonas genera.
Depending on the species of bacteria that is infecting the plant, it might just be a few leaves that are impacted or it could be the entire specimen.
Symptoms generally appear as lots of little spots or v-shaped lesions that spread and turn the entire leaf brown.
The spots are dark, ranging from brown to black, and they can be dry or appear water-soaked. They may or may not have yellow margins.
When a leaf turns entirely brown and collapses, it will be mushy and stinky. If you’ve ever smelled the water in a vase after it has been left for several days, it smells a lot like that.
Usually, the spots are inter-veinal, which means they appear in between the veins but not on the veins themselves. Most develop on or near the margins of the leaves, but they can start at the stems or in the middle of the leaves as well.
You can prune off any symptomatic leaves, but if the entire plant is impacted, you’ll need to toss it out because there is no cure for bacterial leaf spot.
3. Bacterial Wilt
While bacterial issues aren’t extremely common on houseplants Ralstonia solanacearum (formerly Pseudomonas solanacearum) can infect over 200 different species, causing the foliage to droop and wilt.
When you see the plant wilting, you might check the soil, thinking it needs some water, only to find that it has ample moisture.
Sometimes bacterial wilt starts as one section of the specimen wilting; other times, the whole plant starts to show symptoms. The pathogen thrives in warm, humid conditions.
Unless the specimen is one that you prize and can’t replace, it’s usually best to toss it out if it becomes infected.
If you want to try and save it, you will need to remove the plant from its container, clean the pot with hot, soapy water, and then wipe it with isopropyl alcohol.
Remove all of the soil from the roots by brushing it away and then rinsing it off using lukewarm water.
Repot in fresh soil in the cleaned container and then treat the plant with a bactericide.
Follow the manufacturer’s directions carefully as some of these can be toxic if not handled appropriately.
A product called Procidic uses the power of citric acid to kill bacteria is appropriate.
Procidic
Snag a 32-ounce spray, or 16-ounce or gallon-sized concentrate at Arbico Organics.
4. Damping Off
Damping off is a common disease caused by pathogens in the Fusarium, Pythium, or Rhizoctonia genera.
If you’ve ever tried your hand at starting seeds and the seedlings collapsed with a mushy base, then you’ve already encountered this disease.
It’s most common in young plants, but it can show up in older specimens, though it’s rare.
Damping off can cause rotting roots and a fluffy white growth on all parts of the specimen, along with stunted growth or plant death.
There is no cure for damping off, so prevention is key. Learn more about damping off in our guide.
5. Fungal Leaf Spot
Fungal leaf spot is a broad term that encompasses a broad range of species, symptoms, and causal pathogens. As the name suggests, the symptoms involve spots on the foliage.
Most fungi travel in water, so they need moisture to spread and reproduce.
As part of our preventive measures, we need to focus on keeping water where it belongs, which is in the soil, and not where it can cause problems, like sitting on the leaves and stems.
That means providing enough space so your houseplants have good air circulation and watering at the soil level or using the bottom watering method. Take care not to overwater or spray humidity-loving species too often.
The other part of the equation is protecting the plant so that it isn’t injured, which creates an opening for pathogens to enter through.
Plants in areas that have lots of traffic are often injured by people walking by. Too much pruning or pests can also create openings for pathogens. Excessive fertilization can also leave houseplants exposed to pathogens.
Let’s talk about some of the most common fungal leaf spots.
Myrothecium leaf spot is caused by the fungus Myrothecium roridum. It can infect species in the Anthurium, Pilea, and Aglaonema genera, as well as many others.
It usually causes dark spots on the foliage, but it can also cause crown and stem rot on some plants.
Fusarium fungi can also cause leaf spots, especially on Dracaena species.
It’s also common on aloes (Aloe spp.), haworthia (Haworthia spp.), ponytail palm (Beaucarnea recurvata), spider plants (Chlorophytum spp.), and yucca (Yucca spp.).
This pathogen can also cause root and crown rot.
6. Gray Mold
The same fungus that is famous for destroying tons and tons of strawberries every year and improving the flavor of wine, Botrytis cinerea, can also wreak havoc on houseplants. It’s massively destructive in greenhouses.
The pathogen enters plant tissue via opening like injuries, faded flowers, or pruning cuts. Overfertilized specimens in moist conditions are also susceptible to infection.
Prevention includes removing any debris from around the plant. Those occasional dead leaves? Don’t let them hang out on the soil surface.
Try not to allow houseplants to become damaged by pets or people brushing up against them, and don’t overfertilize or overwater.
If your houseplant is infected, you’ll typically see brown, soggy spots on the foliage and stems. As the disease progresses, you might see gray, fuzzy fungal growth.
Many strains of this disease have become resistant to fungicides, so it helps to rotate your treatments.
Buy a couple of different products with different methods of treatment. A product that contains Bacillus amyloliquefaciens strain F727, B. subtilis, potassium bicarbonate, Streptomyces strain K61, or citric acid can be effective, especially when rotated.
There are even products developed just to address this disease; that’s how big of a problem it can be.
If you want to try a targeted product like that, head to Arbico Organics and pick up some BotryStop WP, which targets botrytis with the beneficial fungus Ulocladium oudemansii (U3 strain).
BotryStop WP
It is available in 12- and 30-pound containers.
Whatever you use, follow the manufacturer’s directions for how often you can use the product and then each time switch it with a different product.
Go back and forth between the two products to avoid fungicide resistance.
7. Powdery Mildew
Powdery mildew isn’t just a problem in your veggie garden, covering your zucchini in the height of summer. It can attack houseplants, too.
In fact, it’s pretty common on species like African violets, begonias, kalanchoe, and poinsettias.
Watch for a white or gray powdery-looking coating on the foliage.
You can rub it off with a moist cloth or your finger, but this only helps you diagnose the problem, not get rid of it, because the fungus is systemic, not isolated to the surface of the plant tissue.
There are dozens of different pathogens that cause powdery mildew and many of them are species-specific.
If you find that your houseplant is infected, isolate it to avoid spreading the problem. Fortunately, powdery mildew is one of the easiest diseases to treat and get rid of.
You can use all kinds of treatments, like milk and baking soda, or fungicides like sulfur, copper, and neem oil.
Read our guide to powdery mildew for tips about how to use these treatments to eliminate this common disease.
8. Root and Crown Rot
Root and crown rot is a generic term for any disease that causes infection and rotting in the roots and crown area.
Most of the time, it’s caused by fungal pathogens, but bacteria and oomycetes can cause rot, too.
In houseplants, rot is typically caused by pathogens in the Alternaria, Armillaria, Cylindrocladium, Fusarium, Phytophthora, Pythium, Rhizoctonia, and Sclerotinia genera.
Without exception, rot needs moisture to take hold.
Overwatering and soggy soil is a sure-fire way to invite root rot, while watering from overhead so water can pool on the leaves or stems can lead to crown rot.
High humidity and crowding can invite these pathogens as well.
When crown rot is present, you can see it. There will be areas on the plant that will be mushy and black or brown. They might be slimy and stinky, too.
Root rot is a little harder to identify because it happens under the soil where you can’t see it until the symptoms appear on the aboveground parts.
These symptoms will generally start as yellowing or browning of the leaves and leaf drop, and possibly stunted growth. If you dig down, you’ll find brown or black, mushy roots that might smell rotten.
I like to treat crown and root rot with a biofungicide that attacks a broad number of pathogens. My go-to is Mycostop, which contains a beneficial bacteria called Streptomyces Strain K61.
This bacteria is derived from sphagnum peat moss and is effective against every species listed above.
Mycostop Biofungicide
Pick up Mycostop in five- or 25-gram packets at Arbico Organics, but be sure you use it immediately after opening because it rapidly loses effectiveness.
Depending on the product, you’ll want to apply it every two weeks or so until new, symptomless growth develops.
For root rot, soak the soil and if there are symptoms on the aboveground parts, spray the leaves and stems. Honestly, I would always treat both the soil and the foliage and stems just to be safe.
Additionally, in the case of root rot, it helps tremendously to remove the plant from the pot and brush the soil away before trimming any dead roots at least half an inch into healthy growth.
Then, spray the roots directly with Mycostop.
Clean the container thoroughly with hot soapy water and repot in fresh, clean soil.
Learn more about root rot in houseplants in our guide.
9. Rust
Rust is a common fungal problem that affects many plants growing outdoors, and while it’s much less common in houseplants, it’s not unheard of. It’s particularly common on cacti.
There are species-specific fungi that cause aloe rust (Phakopsora pachyrhizi) and begonia rust (Coleosporium solidagin) for example.
There are over 5,000 species that can cause rust, so many houseplant favorites are susceptible.
The disease spreads through water, so avoid overwatering or watering from overhead and allowing the foliage to remain damp. Don’t crowd plants or keep them in an area that’s too humid, either.
As the name suggests, the disease looks like your plant is rusting, with orange streaks or spots on the stems and foliage.
Fortunately, it’s pretty easy to treat with a product that contains B. subtilis, like CEASE, which we discussed above.
10. Stem Canker
Stem canker is another generic term for diseases that cause lesions or rot at the base of the stem. Typically, it looks like a dark, sunken area either one one side or encircling the stem.
In most houseplants, fungi in the Alternaria, Lasiodiplodia, Neofusiccocum, Phomopsis, and Sclerotinia genera cause this disease.
As with most fungi, these pathogens need moisture to thrive, so crowded, overwatered specimens are most susceptible.
If the plant has multiple stems, you can prune out the infected ones. But if there is just one main trunk or stem and it’s infected, there isn’t much you can do.
You can try treating it with any fungicide, but chances are the plant will need to be disposed of.
11. Viruses
There are so many different viruses that cause symptoms in their hosts including tobacco mosaic virus (TMV), impatiens necrotic spot virus (INSV), and dasheen mosaic (DsMV).
Most are species-specific, meaning they only attack one or a few related species of plants.
Generally, most viruses are spread by insects or on infected plant material and tools.
The symptoms vary depending on the type of virus, but usually you’ll see yellow or cream mottling and discoloration on the foliage.
As with most viruses that make humans sick, there is often no treatment that can completely cure the problem. In humans, we often let the disease run its course.
You can do the same with plants, but the diseases will never go away. Plus, you run the risk of infecting other specimens in your collection.
But if you aren’t particularly worried about spread, viruses usually won’t kill the plant, and so long as you keep it healthy, it can survive for years. Otherwise, bag it and toss it.
Show Diseases the Door
Diseases are a part of gardening, they will come and go, despite your best efforts. But as you gain experience, you start to learn how to avoid them.
Keep your plants appropriately watered, well-spaced, always use clean tools, and you won’t have to worry about diseases as much as gardeners who don’t practice good sanitation.
Are you dealing with a disease in your houseplants? Tell us what you’re facing or what symptoms you’re seeing and maybe we can help you narrow down the problem.
And for more information about growing houseplants, read these guides next:
