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Rex Begonia help... spots on leaves...

St. Thomas, Canada

I have been collecting some rex begonias since the beginning of spring. They have been doing well all year so far except for the last few weeks when one of them started to get these spots on its leaves, it has spread to a few other plants since then and I am afraid that they are all going to end up getting it and I am going to lose them all.

I have them all in the house, west and east facing windows. No direct sunlight, and I have them on pebble trays. I live in Southwestern Ontario, Canada. I have stopped watering them as much as I was in the summer when I noticed that my plants were getting these spots, thinking that I could be overwatering for the time of year possibly? One plant has brown spots on it and the other one has what I think is powdery mildew and the spots as well. I have tried looking it up on the internet but I am not 100% sure of what it could be.

I went out to the local nursery where I had got most of my begonias and brought a few of the leaves to show them and see what they would recommend. They recommended Safers Ready to use Defender garden fungicide. I tested it out on one plant because I am not sure if I should be using a garden fungicide on a houseplant? Nothing seems to be happening. I would prefer to use a natural home remedy if at all possible.

If anyone could help me identify what the problem is with my beloved plants so I can get them better it would be greatly appreciated.

Thumbnail by JennieV
St. Thomas, Canada

Here is a photo of the other plant.

Thumbnail by JennieV
(Zone 1)

Looks like fungus. I don't grow Rex Begonia's but I use this Safer Fungicide: on a lot of houseplants. I don't know if it is something that can be used for Rex Begonia's or not but hopefully someone more knowledgeable will come along with some advice.

Fungus can be caused by temperature changes as well as lack of air circulation. You might want to consider using a small fan on low speed in the room.

St. Thomas, Canada

Thanks for replying to me plantladylin :) I have checked on here quite a few times today hoping that someone would have an answer for me. I will try the fan and see if it helps. I am keeping my fingers crossed.

(Zone 1)

The fan will help with air circulation but I don't think it will stop the progression of the fungus. Hopefully someone will come along and see your post before long. Weekends are kinda slow around here sometimes, but keep watching folks will be along at some point to respond with tips and suggestions.

St. Thomas, Canada

I read somewhere to use mild cooled chamomile tea as a spray for fungus... now I am wondering if I should try that. Has anyone tried this with any success on begonia's?

(Zone 1)

I googled and found this article but I don't know anything about using chamomile tea for plants:

There was just a discussion on the African Violet Forum last week about powdery mildew on someone's plants. You have to be a paid subscriber to access that forum so I will go over there and see if I can find the info and come back let you know. Meantime, here's a link to some information regarding powdery mildew on AV's which would be the same for begonia's:

(Zone 1)

Ok, here's what some folks stated on that thread about powdery mildew.

Sudden change in temperature (colder) now that autumn is here and also environmental changes can cause an outbreak of powdery mildew.

Powdery Mildew is caused by a fungus, which occurs when there are sudden changes in temperature and poor air circulation.

A couple of people use Neem Oil for control of powdery mildew and other pests and diseases. Schultz Garden Safe Fungicide 3 (with 0.9% neem oil) was another suggestion. One lady said she uses Neem Powder and Cinnamon Leaf Oil. Another lady said she uses a light spray of Lysol. I would be careful with the amount used on foliage so as not to clog the pores.

Neem is a natural product that comes from a tree, used on ornamentals, fruits and vegetables:

More information for Neem Oil:

I hope you are able to get control of the mildew on your beautiful begonia's. Good luck and keep us posted on what works for you.

St. Thomas, Canada

Thanks again Plantladylin for all your tips and suggestions. I really appreciate it :) It is nice to know that someone is willing to help me out. I really like this site. I can spend hours on here just looking at everything. There is so much to learn and so many interesting topics on here.

I went out and got a spray bottle tonight that gives out a fine mist to try out the chamomile tea remedy tomorrow. I researched it a bit and I am really hoping this works. I am going to spray the rest of my begonia's as a preventative measure. I would rather be safe than sorry. Hopefully I have some success with that.

I do have lysol around the house but it makes me worried to give the one plant a double dose with different sprays in the matter of a few days. It is not looking so good. The leaves are getting dried up on the edges and I don't know if it is going to recover. There is another plant with a few spots just developing that I will spray tomorrow. I will let you know how it works out.

I will have to search for any neem oil products around here. I couldn't find anything tonight when I was out.

One thing that is on my mind but I am not sure if it means anything or not. I have african violets right by all my begonias. I had just moved them there a few weeks ago when the temperature started to drop in the sunroom where they had been living all summer. When I think back, the begonias started to get these spots just after I moved the AV over there. I am now wondering if somehow they could have given my begonia's a mildew or fungus? Or if it is just a coincidence and I am thinking too much into this? As far as I can see the AV are doing really well. There is the odd leaf that had been sunburnt from the summer sun but the AV are all healthy looking, no sign of mildew or anything out of the ordinary.

Dublin, CA(Zone 9a)

I'd probably stay away from using things like Lysol on plants--it's great if you've got mold in your bathroom but it's not designed for use on plants so you never know if there might be some ingredients in there that can harm plants. Since there are antifungal products that are made specially for plants I don't see any reason to take a chance with something like Lysol. I don't know whether begonias have anything special about them that would mean you can't use the typical neem, etc that have already been mentioned. I also don't think your AV's gave powdery mildew to your begonias, particularly if they don't have any symptoms of it themselves. The only way I can think that they could have contributed is if the level of crowding in that area became excessive when you brought them over...poor air circulation can contribute to powdery mildew.

St. Thomas, Canada

I never tried the lysol. I did however try the chamomile tea remedy. It has taken the mold away but there are still spots on the plants underneath where the mold was... does anyone think that this is good news or should I get my hopes up? I was thinking that spraying the mold spots with the tea just took away the mold and it will just grow back in time. I have my plants better spaced out now and the ones with mold away from my other plants and each other as well.

The one plant looks better but the other one a bit worse. I also sprayed my other begonia's with the tea lightly twice as a preventative.

Thank-you everyone for your help!

SW, WI(Zone 4b)

I've used the tea as a topical remedy for soil that had mold issues, and it did work.
I've never used it as a spray.

If the mold is still gone after the spray dries, there's a good chance it worked!

The spots will remain - they won't go away.

St. Thomas, Canada

Thanks Nan! I have been so upset about my begonia's. Do you know if it will be ok to have these spots on the leaves? Will they just not be so nice to look at? I can live with them not looking so nice, I just don't want them to die. It seems like there are new spots everyday though. They are small but there is no mold on them.

SW, WI(Zone 4b)

The spots will be OK, just - as you say - not nice to look at. say there are new spots appearing every day? That could indicate that you haven't solved the problem yet.

When you sprayed the 'tea' on the plants...were they receiving any direct sunlight? The 'new' spots could be burn from the sun hitting the water droplets.

If not, then perhaps they have a fungus as Lin indicated above, and it needs something 'stronger' than the tea to eradicate it.

(Lynn) Omaha, NE(Zone 5a)

The spots could be getting worse because the leaves are wet,especially if it is a fungus.Any garden product safe for indoor plants should be safe for Begonias,unless it specifically says it's not.The Safer line works well.
Are there any spots or fuzzy looking areas on the rhizhomes or stems?


(Lynn) Omaha, NE(Zone 5a)

Here is a little info.

St. Thomas, Canada

When I misted the leaves there was no sunlight on them, it has been overcast most days recently. I only misted them twice with the tea and that was very lightly. I misted late morning one day and early afternoon the other day. The spots were there before I even started misted with the tea so I am not sure if I am making it worse by getting the leaves wet. I don't think I will use any more of the tea just in case.

The two plants that had powdery mildew on them I have sprayed repeatedly with the tea, I have also taken off most of the leaves that were bad. The mold is gone and has been for awhile but the leaves are not doing that well. I could have overdone it with the tea with these two plants.

I will try to get more photos on here tomorrow of what the spots on the other plants look like. Maybe that might help.

I will most likely have to go with the fungicide. I just have a baby and pets in the house so I was hoping not to have to use it.

There are no spots or mold on the stems or anywhere else on the plants. It is just on the leaves.

I was reading up on that link above...


1) It says that Rex and tuberous types are not systemically infected... Can someone explain to me what that means?

(Lynn) Omaha, NE(Zone 5a)

When something is systemically infected the entire plant,roots,rhizhomes,stems and leaves are infected.If it is not systemic,it is only affecting part of the plant (in your case,the leaves).The rest of the plant is still healthy.

St. Thomas, Canada

Thanks for the explanation Ibrabec! I was getting confused reading up on so many things. It all starts to look the same after awhile :)

That is good news I hope, I still want to save my begonia's!

There has been some good light today. It is now snowing so the good light is gone but I got a chance to check out my plants a bit more closely and there are not so many spots on the leaves as I thought there would be. I have taken off most of the bad ones though the past few days so I am hoping it has stopped spreading at least. I am in the process of taking care of my other houseplants right now and rearranging some of them. Last I am going to give the begonia's some of the fungicide and I am hoping it helps.

SW, WI(Zone 4b)

What I meant when I asked if the sun had been shining on the 'wet' leaves, was that I thought that was a possibility for the *newly appearing* you still have new spots appearing?

If you're concerned about using anything 'chemical' (and I don't blame you one bit!) should try to get ahold of some Neem oil.

I got mine via mail order after Al/Tapla recommended a specific product....I'll try to find the thread....I know it said 'cold-pressed' was better than many of the Neem products out there.

(Lynn) Omaha, NE(Zone 5a)

To be a little more clear,systemic means it affects the whole plant.I probably should have used that word,rather than infection.
I'm not sure yet,but I suspect your plants have some type of leafspot and although you will lose leaves,the plants should recover.

St. Thomas, Canada

I am happy to say that things have started to look better with my begonia's. No new spots developing anyways. I am crossing my fingers that things get even better :)

Thank-you everyone for your help!

(Lynn) Omaha, NE(Zone 5a)

That's great!! Let us know.

St. Thomas, Canada

I will keep everyone posted on how they are doing :) I love these plants!

SW, WI(Zone 4b)

That *is* good news!

It's always nice to hear of an organic method that works....I'd never 'sprayed' the tea before, but might give it a try in the future if needed.

St. Thomas, Canada

I am sad to say that most of my begonia's are not doing well again. The spots came back and they have lost so many leaves that I don't want to take off the last remaining leaves for fear of them dying completely. I don't think they are going to get better. I am ready to give up on the one window full of sad looking plants. I did read somewhere before that I should discard all infected plants but with not really knowing what is wrong with them I didn't want to.

Would anyone know if I would be able to let them die back completely, let them rest all winter and when it is spring start to water them again in hopes that they will come back? Or would the fungus still come back and I would be faced with the same problems next fall?

(Lynn) Omaha, NE(Zone 5a)

I"m sorry to hear about your plants.What you can do is cut the rhizhomes into pieces and put them in a sterile mix such as half peat,half perlite in a covered box or tray.They should start putting out new growth fairly soon.Moisten the mix before placing the rhizhomes in.It should be kept moist,but not wet.Put them under lights or in a semi-shady area.I would put different plants in seperate boxes,in case there is any disease affecting the rhizhomes.

St. Thomas, Canada

I have some good news and some bad news... Most of my begonia's are recovering is the good news. Four of them are doing better than I would have thought even. The bad news is that two of them I had to destroy because they were getting really bad with the spots no matter what I did and I didn't want to risk them spreading whatever it is to the others. I think the rest are on the road to recovery. They are slow to grow new leaves but there are no spots on them either. No new spots on anything (knock on wood) for about 3 weeks now. I am very happy about this and just thought that I would let everyone know! :) I am hoping the rest make a total recovery by the spring!!!

(Lynn) Omaha, NE(Zone 5a)

Great Jennie,
I hope they all come through for you.

Santa Fe, NM

Despite all the good information about what conditions may contribute to powdery mildew, the fact is that anything that stresses plants even slightly can lead to an outbreak. Dampness is not necessarily the culprit. I'm currently living in very dry Santa Fe, NM and two weeks after bringing a new begonia into my house, all my begonias, healthy for years previously, were showing signs of infection.

You might have success with more "natural" sprays (I didn't--in fact, waiting to see if the more natural remedies were working only led to worsening of my outbreak), but if you want to really knock out the infection, use a product like Safer Garden Fungicide at the first sign of infection and use it weekly for about a month. Spray top and bottom of leaves, as well as stems of cane begonias. Spray to thoroughly wet all surfaces--the outbreak is caused by tiny spores, so you want to create an completely inhosiptable environment for their reproduction.

You may as well remove all infected leaves before spraying. They will never look perfect again and the more leaves on the plant, the more spray you'll need to use. I wear latex or vinyl gloves when spraying to keep the spray off my skin as I turn the leaves to get the spray on the bottom of them. Keep any pets or children away from the spray until it has dried--which is not to say that anyone should eat the leaves that have been sprayed with sulfur either, but don't let it drip on anything alive except your affected plants. It's not horribly toxic, but it's not edible.

The spray will leave the beautiful leaves of your begonias looking dim and unattractive, but resist the desire to clean them for the month of spraying. After you're sure the cycle of infection has been interrrupted, you can wash the sulfur spray residue off the leaves. It can take some rubbing to remove it, so you may want to employ a small, fairly soft paintbrush.

If you can nip the outbreak in the bud with diligent weekly spraying, you won't lose any plants and they will regrow the leaves you removed. Remember, though, those small spores can start another outbreak if the conditions are right (or wrong!), so always keep some sulfur spray handy. Good luck!

Volcan, Panama

A lady who lives near me grows Rex Begonias to sell and she periodically sprays her plants with Ridomil Gold MZ 68 WP. It is a combination contact and systemic fungicide that is used on various vegetable crops. It is not phytotoxic. I live in Panama where we have a 9 month rainy season and during that time the humidity is extremely high and so mildew is a problem. The wild Begonias growing in the woods and out-of doors never get infected in spite of all the rain but Rex Begonias are not native to here. Anyway a 50 gram packet costs less than 2 dollars at the local coop which is enough for about 10 gallons of spray. I think a teaspoon is about 5 grams.

Merrill, WI

I have a collection of aprox 30 Rex's. So far I have had them for over the winter in Wisconsin, so I bring them inside my hairsalon in direct light during the day, at night I turn the heat down to about 50. I donot spray their leaves. For I figured they may get water spots or start fungus because they are fairly close together. I water them maybe once per week , then wait until the soil is pretty dry. Once per month I fertilze with jacks fertilizer .mayb 1/2 strenght. But over water for mine will cause spots and crispy edgesand every time I water I check under the plants for dried leaves or anything that dosent look good and take it out so it dosent start anything. I would like to put them in some containers this summer , but don't know yet what plants they would be compatable with an any ideas?

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