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Help identifying houseplant disease #857356

Asked January 13, 2024, 3:43 PM EST

My pothos plants have developed a problem (after 20 years of problem-free existence!). I can’t find anything online that looks like this problem for pothos: brown spots that grow in size to eventually destroy the entire leaf. See photos showing spots at varying stages of development. I hope you can help me diagnose, then ameliorate this problem!

Windsor County Vermont

Expert Response

Hello Robert,

Thank you for reaching out to the EMG Helpline. We're sorry to hear about the problems you're experiencing with your pothos. I have a few questions that might help with a diagnosis:

What kind of lighting and humidity do your plants have?
What kind of watering and fertilizing schedule are you following?
How fast do the spots grow once they form?
How long has this been occurring and have you tried any fixes yet?

I realize that's a broad question set, but there are several possible reasons for the spots. Given the info I have so far, I've listed some potential causes and remedies below.

1. Most indoor plant issues stem from Issues related to watering. These spots could be caused by overwatering, inadequate watering, or water spots on the leaves. Pothos prefer a drench then dry watering routine. Soak the root ball thoroughly, then allow the soil to become fairly dry before watering again. Do not allow the plant to wilt. It may be difficult to judge how watering is going based on the type of pot that is used (plastic, clay, one drainage hole, many drainage holes, etc.). Avoid top watering and splashing water on the leaves. Only add fertilizer in the spring through fall and in the fertilizing season, you don't have to provide heavy fertilization. If there was an unintentional overuse of fertilizer, you might observe salt deposits on the outside of the pot or surface of the potting media as a white crust.

2. Fungal Leaf Spot. Here are some examples showing fungal leaf spot on houseplants: https://extension.umd.edu/resource/fungal-leaf-spots-indoor-plants/. This can be improved by reducing humidity and picking off impacted leaves.

3. Bacterial leaf spot. Usually occurs in overly wet conditions. Here's an example of this kind of infection in Pothos: https://plant-diseases.uada.edu/img/plant-category/house_plant/pothos_bacterial_leaf_spot.jpg. Individual leaves with spots can be picked off and destroyed. Reducing moisture and increasing air circulation can help.

4. Issues related to lighting. Pothos prefer a well-lit area without direct sunlight. It's probably unlikely, but sunburn could happen if the plants are in direct and intense sunlight.

Please feel free to respond with information about the current growing conditions and let us know if the information provided is helpful.

Happy Gardening, Jessica, UVM Extension Master Gardener Programwww.uvm.edu/extension/mastergardenerWe do not intend to endorse any products we mention or criticize products we do not mention. When we include a link to a resource that recommends a chemical, it is for informational purposes only; the chemicals may not be registered for use in Vermont. Replied January 16, 2024, 12:37 PM EST

Hello Robert:

Jessica has given you some excellent information and resources. I also want to include the following video that was recently presented by one of our Master Gardeners - https://streaming.uvm.edu/watch/50769/pothos/

I hope this add'l. info. is helpful.

An Ask Extension Expert Replied January 16, 2024, 1:51 PM EST

Jessica,

Thank you so much for all this information! To address your questions:

1. What kind of lighting and humidity do your plants have?

There are 8 plants, of varying ages. All have plenty of light. Some are in direct sunlight for several hours on a sunny day. Others get mostly indirect, but bright sunlight. Others get no direct sunlight ever, but plenty of light. Some are clearly happier than others, but this seems quite unrelated to light (or anything else associated with their locations) and they all are pretty chipper except for the spots. So it doesn't seem to me that lighting is the cause of this issue.

2. What kind of watering and fertilizing schedule are you following?

I soak them thoroughly, then wait for them to be pretty dried out. They let me know when they are getting thirsty (not wilted, but clearly starting to want a drink). This has served them well for at least a quarter century. The leaves don't usually get wet when I water.

I use a slow release granular fertilizer (standard Miracle Gro plant fertilizer) periodically. For years I carefully fertilized this way every 3 months and everyone one was quite happy. In the past few years, it has been less often and more erratic, as I forget and don't get to it. I'm certain they aren't over-fertilized.

They live in a fairly dry environment. Woodstove keeps the air quite dry in the winter, especially for those that sit in the same room with the stove. We have a strong air filter that runs continuously, so there is always some modest circulation. Windows are open every day in summer/fall.

3. How fast do the spots grow once they form?

I don't know. I keep a pretty close eye on them and pick the affected leaves off quickly. If speed is really informative about what the problem migtht be, I can leave some on and track their growth.

4. How long has this been occurring and have you tried any fixes yet?

This seems to have been on-going for maybe two years? Never had this problem before. They moved to a new environment 4 years ago, but this problem didn't seem to develop in conjunction with that move. They did all have a traumatic experience. We were out of town when Covid hit, keeping us away for 3 months. I had set them in a bathtub filled part way with water to keep them watered for the few weeks we meant to be gone, but that evaporated at some point. They were extremely dry, stressed & wilted when we finally returned, but quite amazingly most of them recovered fairly quickly. So being overly wet, then deprived of water might well have heralded the onset of this problem. They also spent that time with limited light. It had not occurred to me until just now, that this undoubtedly traumatic experience may have started something. I was shocked that any of them survived.

The only fix I've tried so far is picking off the affected leaves as soon as I see them.

I routinely sprout cuttings to create new plants, or fill in bare spots that occasionally appear in really old ones. And these cuttings sometimes develop the same spots while immersed directly in water to sprout.

So, in summary, because the plants are of varying age, have varying exposure to direct sunlight, are in pots that allow them to dry out at quite different rates, live in several different rooms I'm puzzled that every one of them has this problem. Some seem more afflicted than others. Because of this is feels to me like this is a disease or some sort of infestation that has spread.

One other bit of information. These plants are of varying ages, but most of them are in years-old potting soil. Because Pothos are so robust and forgiving I've never been careful to start new plants in brand new potting soil. But again, the soil in each originated from a different source, so the soil commonality is merely that it's "old" in each one. I did just start a new plant a little over a month ago with fresh indoor potting soil, so I'll be interested to see if it develops this same problem.

From what you've sent, the problem looks most like bacterial leaf spot. Possibly fungal leaf spot. But the conditions that foster those don't seem to be present here. I'm wondering if maybe some of those that went through the trauma a few years ago experienced genetic damage such that every time I sprout a cutting from those plants I'm just perpetuating the problem? I know this makes no sense, but so far no other explanation seems quite right either.

So ... I will be extremely grateful for anything else you might offer as a possible explanation, and/or solution.

Best regards,

Rob

On Tue, Jan 16, 2024 at 12:37 PM Ask Extension <<personal data hidden>> wrote:

The Question Asker Replied January 17, 2024, 11:36 AM EST

Hi Rob,

Thank you for answering my follow-up questions and providing additional information.

It does seem possible for that pandemic event to be related to the start of your issues, especially considering your long and positive record to this point! I was primarily thinking fungus or bacteria when I responded yesterday. It's difficult to diagnose a fungus from a bacteria without a culture. One additional question for the moment, sparked by the fact that cuttings in water have shown the spots: what is your water source for your plants? It will also be interesting to track the new cutting that has been rooted in new soil to help eliminate soil contamination as a factor.

Jessica,

Water source is well water (artisian well), which runs through a softener to remove the abundant minerals here.

I'm wondering if I was right about the cuttings getting those spots before planting. I know the leaves on some dry up or get ugly otherwise, but I'm now wondering if they get the spot. I'll keep a more careful eye on those. I'm also tracking a newly discovered spot on a quite newly potted plant to see how fast it grows.

On Wed, Jan 17, 2024 at 2:24 PM Ask Extension <<personal data hidden>> wrote:

The Question Asker Replied January 17, 2024, 3:24 PM EST

I've had some bacteria contamination in my home well system, but bacteria could also be present in a watering can, faucet, rain collection barrel, etc.

Please write back to share your observations if you have time!

Help identifying houseplant disease #857356

Expert Response

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