Plant People - Help!

[isabel]

If you are a plant person, I would love your thoughts on this.

I've had most of my plants for at least a couple of years with really no issues aside from fungus gnats every now and then. I clarify that because my plants have always been very healthy. I don't over water them and I've never had issues with root rot.

I was seeing a little more gnats recently and decided to go ahead and treat all of my plants with Bonide. On the day I did this, I took them outside and they got more direct sunlight than they probably should have. I pretty quickly noticed that several of them had leaf burn, but figured it wasn't that big of a deal.

Now it seems like almost all of my plants, particularly the vining pothos-type plants are dying. The stems/roots are rotting. All of these plants were perfectly healthy before I treated them and I feel like there's no way a couple hours of direct sun could do this much damage. I can't really find anything about Bonide harming plants, so while that seems unlikely, it's the only thing that really makes sense to me right now and I'm wondering if I need to try to repot all of them with fresh soil or something.

Anyone have ideas on what's going on? I'm trying to root some of them that have completely broken off at the stems, but I'm nervous it's not going to work. I really love some of these plants and am feeling really stressed that the ones that seem fine right now are going to go the way of the others.

[mala]

How long has it been since you last replanted them? If it's been a year or more I'd replant with fresh soil. It could have become impacted and not as well draining, plus soil loses nutrients over time as the plants use it. Could be there's not enough so plant growth slows down, which means using less water and the soil stays wet longer.

[cap]

Bonide makes a lot of different products. Which specific product did you use and at what rate? How did you apply it? Are you fertilizing? If so, what product (I’ll need the N-P-K ratio), how often, and what mixing instructions do you follow? And to echo the PP, when did you last repot? Have you looked at any of the roots? If you want, add a few more photos. If you think anything else might be relevant, please share that, too.

[Patsy Baloney]

If worse comes to worse, take cuttings and start over. Pothos especially have a will to live. There is no plant I love mistreating more, except maybe snake plants.

[isabel]

Oct 8, 2024 6:05:50 GMT -5 cap said:

Bonide makes a lot of different products. Which specific product did you use and at what rate? How did you apply it? Are you fertilizing? If so, what product (I’ll need the N-P-K ratio), how often, and what mixing instructions do you follow? And to echo the PP, when did you last repot? Have you looked at any of the roots? If you want, add a few more photos. If you think anything else might be relevant, please share that, too.

Bless you. Ok, here's all the details and my update as of this morning.

This is what I used: bonide.com/product/systemic-houseplant-insect-control-granules/. 

I used it as specified in the directions based on the size of the pot (not gallons, but inches). I followed the directions. Sprinkled it on, mixed it into the top of the soil, watered thoroughly. Have not watered since I did this on 9/29.

Yes, I am fertilizing using the Happy Happy Houseplant liquid fertilizer. I did fertilize when I used the Bonide product. I have used this same fertilizer for at least two years now with zero issues and plenty of great new growth. N-P-K analysis is here: happyhappyhouseplant.com/collections/merch/products/plant-food-fertilizer

All plants have been repotted in the last year, with the exception of maybe just a few. The majority of them were repotted early this summer.

Ok, so this morning:

I unpotted four of the plants, three that looked rough and one that didn't. Those included two philodendrons (a philodendron billietiae and one I can't identify), a Scindapsus treubii 'Moonlight', and a begonia maculata. One of the philodendrons (the bigger one) looks perfectly fine. Strong white roots, no evidence of rot. The moonlight had a ton of rotted fine roots in it, but also plenty of healthy white root. I removed as much of the rotted root as possible and repotted it in fresh soil. I am hoping it bounces back. The billietiae is a goner. I have one healthy-ish stem with a node, but the node seems rotted. I cut as much of the rot as I could and put it in water to see if it will root. The begonia roots did not look good at all, but many of the stems/leaves were still healthy, so I chopped that up and put it in water too. I am optimistic about being able to root that one and just start with a new plant. My pilea peperomioides rotted off at the stem, so I took off all the leaves and stuck those in a prop box and chopped the stem until it looked healthy and put it in water.

I did not unpot several standard pothos and a marble pothos, but all are definitely dying and will for sure have significant root rot. I don't think there's any saving the marble (pictured above), so I chopped several huge vines and am propogating it in a prop box with sphagnum moss and cut some individual stems with nodes to root in water. That said, I do have at least one pothos that is seemingly fine. I didn't unpot it, but the leaves look fine and the stems near the soil seem healthy so far. I am assuming all the regular pothos will die and I'm not going to both trying to prop those.

Other plants that seem fine right now: fiddle fig, monstera, jade, snake plant, ZZs, and ponytail palm. 

I am really stressed about the monstera and ZZs in particular because I've had them for several years and it would be $$$$ to replace them at that size. Again, I haven't unpotted these. The monstera roots that I can feel on the surface seem strong and healthy and there's no evidence of stress on the leaves. I would rather not unpot that because it's huge and heavy and would be a big pain in the ass. However, it's gone the longest without repotting for that reason. The ZZs also seem fine. No evidence of stress in the leaves, stems are thick and strong. I think the jade is ok too, but I want to unpot that and check on it. The ZZs and jade were both repotted earlier this year.

No additional pictures. I was rushing this morning trying to triage as much as possible before I had to get to the office.

[mala]

IME begonia maculata will root quickly in water, for what it's worth. The pilea, too.

Did your humidity spike? Maybe the water was just not evaporating. Or a week or two with less sun could also affect growth.

If you have a wooden towel you could try sticking it all the way down in the ZZ and monsters. That would at least give you some indication of whether the soil is wet down at the bottom of the pot. If it is you can pull them out and check the roots.

Edit, also I'm going to assume you looked for other pests as well as the gnats and didn't see any evidence.

[isabel]

Oct 8, 2024 12:20:18 GMT -5 mala said:

IME begonia maculata will root quickly in water, for what it's worth. The pilea, too.

Did your humidity spike? Maybe the water was just not evaporating. Or a week or two with less sun could also affect growth.

If you have a wooden towel you could try sticking it all the way down in the ZZ and monsters. That would at least give you some indication of whether the soil is wet down at the bottom of the pot. If it is you can pull them out and check the roots.

Edit, also I'm going to assume you looked for other pests as well as the gnats and didn't see any evidence.

That’s a good idea. The jade and ZZs are dry on top. I’ll check the bottom. The monstera isn’t wet, but not totally dry either. I do keep it more moist than the others for obvious reasons though.

Yes, checked the leaves and soil. I don’t see any other indication of other pests.

I live in denver and it’s quite dry here. I don’t think the humidity has really been any higher than normal and we haven’t been getting rain. Is it possible that I watered those too soon after the last time and that’s what’s causing this? I don’t water on a schedule, and some of these probably weren’t ready to be watered, but I wanted to treat them all at the same time. Just seems crazy to me that one instance of overwatering would cause this level of damage, especially on the pothos which are pretty forgiving.

[cap]

I think that what you're seeing is phytotoxicity from the pesticide you applied. I was pretty surprised to see this, as the active ingredient in the product you used is imidacloprid, which in a product called Marathon that we used to use pretty regularly in the greenhouses that I run. As far as I know, we never had any phytotoxicity issues, but a search revealed a couple of studies (in peer-reviewed publications, done by plant scientists at land-grant universities, so I absolutely trust the research) where phytotoxicity was observed in greenhouse-grown tomato and cucumber transplants.

I was honestly pretty surprised by this, because imidacloprid is quite commonly used. Intense sunlight can make plants more susceptible to phytotoxicity, so that could have played into it.

I think that you're taking the right course of action on the plants that were damaged. I also think it's really unlikely that the plants that are not showing any symptoms will start showing them, so they will most likely be fine.

If you need to control fungus gnats in the future, you may want to consider a product like Gnatrol, which contains the fungus Bacillus thuringiensis - it infects the larvae and feeds on them, killing them. I'm not sure if you can get Gnatrol in small enough quantities for homeowner use, but there might be other products that have the same (or similar) fungal pathogen.

Let me know if you have more questions!

ETA that one of two times of watering too soon won't cause issues like what you're having. 

[mala]

To piggyback, I use mosquito bits to control fungus gnats in houseplants. Soak a tiny bit in hot water and when it cools use it to water the plants. In the bioactive terrarium I use beneficial mites that feed on the gnats. Can't use mosquito bits there cause of the isopods.

[caddywompus]

I have several peace lily’s that tend to get fungus gnats. This always works for me: To get rid of fungus gnats, mix a solution of one part hydrogen peroxide with four parts water. Pour the mixture onto the soil around the infested plant. Repeat several times over a week or two.

[isabel]

Oct 8, 2024 14:43:27 GMT -5 cap said:

I think that what you're seeing is phytotoxicity from the pesticide you applied. I was pretty surprised to see this, as the active ingredient in the product you used is imidacloprid, which in a product called Marathon that we used to use pretty regularly in the greenhouses that I run. As far as I know, we never had any phytotoxicity issues, but a search revealed a couple of studies (in peer-reviewed publications, done by plant scientists at land-grant universities, so I absolutely trust the research) where phytotoxicity was observed in greenhouse-grown tomato and cucumber transplants.

I was honestly pretty surprised by this, because imidacloprid is quite commonly used. Intense sunlight can make plants more susceptible to phytotoxicity, so that could have played into it.

I think that you're taking the right course of action on the plants that were damaged. I also think it's really unlikely that the plants that are not showing any symptoms will start showing them, so they will most likely be fine.

If you need to control fungus gnats in the future, you may want to consider a product like Gnatrol, which contains the fungus Bacillus thuringiensis - it infects the larvae and feeds on them, killing them. I'm not sure if you can get Gnatrol in small enough quantities for homeowner use, but there might be other products that have the same (or similar) fungal pathogen.

Let me know if you have more questions!

ETA that one of two times of watering too soon won't cause issues like what you're having. 

This feels super validating based on the scenario. I felt like it had to have been the pesticide but couldn’t find anything about it being harmful. Mixed with a good amount of direct sun though, I can see how that would change the dynamic.

I’ll look into that for fungus gnats going forward. I’ve used the HHP product for that in the past and while it seems to work, it’s kind of annoying to use. I have so many regrets now though. lol

I’m keeping a close eye on my other plants but they continue to look fine this afternoon and the roots of my monstera are nice and firm under the soil (I dug my hand in there).

Thank you so much for weighing in! This gives me some peace of mind.

[mala]

I think we need a plant photo thread Maybe not today though.

[isabel]

Oct 8, 2024 19:29:08 GMT -5 mala said:

I think we need a plant photo thread Maybe not today though.

Give me a few months. 😭

[mrspez07]

I've had good luck (in the Denver area) with the hydrogen peroxide treatment for the gnats.