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Begonias Garden Clinic House Plants

How do I treat powdery mildew and potenital leaf spot on my begoinas?

4 years ago

last modified: 4 years ago

I recently discovered powdery mildew on my Begonia Maculata Wightii. I'm SO upset! I have wanted this plant for so long and I finally got one from Etsy. Not even a month after receiving it, I discovered the mildew. I also think it may have leaf spot. There is no way I am able to take a healthy cutting, but the plant is still putting out new leaves so I hope I can rescue it!

My Begonia Maculata Wightii was sitting next to my Begonia China Curl. I know, I probably should have quarantined the new plant, but we live and learn I suppose. I have started to see reddened spots on the China Curl, so I believe I need to treat this one for powdery mildew and leaf spot as well.

I am particularly interested in using homemade fungicide to treat. I have read that a potassium bicarbonate solution is great for killing and preventing all kinds of plant ailments. Does anyone have a go to recipe for homemade fungicide? I am especially interested in those using potassium bicarbonate since I already have it on hand, but I will take any advice I can get!

Thanks for your help!

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Comments (7)

hc mcdole
4 years ago
Milstop is a brand of fungicide that uses potassium bicarbonate (a tad expensive) and I've used it in the past with pretty good results. If I recall the ratio is one TBSP per gallon of water.

Mildew is the bane of begonias - especially the polka dot canes and many others as well. The spores are everywhere so it isn't your fault or the store's or the grower's. The spores are just waiting for the perfect conditions to start growing and reproducing - usually cool, damp conditions. Remove the worst affected leaves. You may have to completely remove all the leaves if they are really infected and spray the stems all around, the soil, maybe the pot. New leaves will come out and eventually new stems from the roots if all goes well. This pattern occurs every year unless you have a really "clean environment" with no mildew spores present or very low levels. Once you realize this, life gets a little easier as you know what to expect in future seasons.

It is a great grower in summer but a bit of a prima donna in winter. I wished I had known that over 10 years ago. It did its best the first year I bought it in 2009.
Crystal Ransom
Original Author
4 years ago
Thank you so much for the info! I’m new to plants and this has been a huge help. Your begonias are BEAUTIFUL! I did look into the Milstop and it’s a little out of my price range unfortunately. And I don’t believe I need a 5lb bag. I’m considering using potassium bicarbonate mixed with water to see how that does. Hopefully my begonias will make it through to be as big and beautiful as yours!
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Chris, not to minimize the possible damage the mildew has already done, have you tried other formula..other than the fungicides to treat this problem. The mildew can indeed cause damage in that it obscures sunlight and photosynthesis from the leaf of the plant. Usually we are told to try to improve the air circulating thru the bed and it is caused from the hot temperatures and the moisture laden air. Unfortunately the advice is to remove any and all damaged or covered portions of the plant. If this includes the stems, then ...sorry, them too. There are a number of remedies and one is two TBSP baking soda.....to 1/2 tsp vegetable oil...to a quart of water. (in Canada...that's a litre) You can add 1/2 tsp dishsoap to help the oil emulsify when shaken---not stirred. You might also consider trying to increase the plant's drainage capability by adding an amount of builder's sand to the soil under the plant.
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hc mcdole
4 years ago
I went through 2 or 3 buckets of Milstop. Yeah, it is a tad high. Neem oil is another one you can use but it is pungent smelling so I swapped it out for Orchard spray (sulfur which has its own odor). You can look through old threads on mildew as there are many helpful suggestions.

If you had a huge greenhouse like the Atlanta Botanical Garden then you can grow it like this - I think the height is over 12 feet tall.
ken_adrian Adrian MI cold Z5
4 years ago
if you havent already.. separate the plants as best you can ...

read a bunch of these: https://duckduckgo.com/?q=potassium+bicarbonate+homemade+fungicide&t=ffcm&ia=web

by the time you read thru a couple.. you ought to get the jist ...

do not spray in sun ... or on hot days ... etc .. all the general rules .. adding actual leaf damage/burn to your problems wont accomplish much ....

and here is a truism.. many say.. you arent a green thumb.. until you have killed every plant.. 3 times ... so if you lose ... so be it ... try again.. and trust me.. you will have learned something for the next time you try ...

welcome to the forums... plz come back often ...

ken

ps: it is usually helpful to include your location.. big city name ... in this case.. im not sure if you are still holding these indoors ... as i would be here in MI ... or if they are already outside ... and if they are outside .. did you harden them off before they went outdoors ... can we rule out leaf damage from shipping.. transplanting.. sunburn ....etc ... there are many things that should be ruled out.. before we start spraying them ...

a pic might help ....
hc mcdole
4 years ago
I finally watched this YouTube video on treating powdery mildew on begonias. I have had it cued up for weeks and decided today is the day to sit through it. About ten minutes long. Cute in a way but annoying in another. She uses Neem oil, dish soap, and baking soda for her cure-all. Pick your poison.

https://www.youtube.com/watch?v=dgKosjWq8RY&feature=youtu.be&fbclid=IwAR1bnq8l3HU0W2lw3RTFbfdIiLAabUtA5d3nn8XB7dCyTCAqJ2e3-mSFgk8
ken_adrian Adrian MI cold Z5
4 years ago
Cute in a way but annoying in another.

==>>> thats why i said to read multiple articles at the link i provided ...

and if you hit the VIDEO link.. there are a couple of those ...

when you find your muse.. the one that speaks to you ... then you will feel comfortable in taking action ....

one of the problems with the WWW ... theres a lot of stuff.. that wouldnt qualify as a muse.. lol .. and too many that should just have their internet taken away .. lol ... [im talking about peeps who comment on news or politics.. not us here.. lol ...]

ken
hc mcdole
4 years ago
Oh yeah, there is a "lot of stuff" on the WWW aka the internet. And you are right that some stuff is full of junk-science. Thank goodness there isn't an internet police so everyone has a voice even if some like it and some don't. Today's political environment has spilled over into every facet of life which is a shame.

Back to mildew issues, B. maculata is one that is very prone to this dreaded fungus and there are many ways to treat it. Whatever method you choose, don't let it fester to the point of death.

My own seed grown hybrid from Mrs. Hashimoto X maculata in late December, 2019. Then mildew set in and I removed all infected leaves but others dropped off by themselves.

I sprayed with Orchard Spray twice now and the plant has recovered somewhat.

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