Plant Diseases/Althea


QUESTION: I am in Houston, Tx. I have 4 blue altheas that are 12 yrs old. They are in a flower bed beneath 5 crepe myrtles about the same age with other annuals also (sparsely planted) and get full sun right now for 4 hours a day and mottled sun another 2. They have always been very full, healthy, and bloom profusely. I use miracle grow & water deeply once a week. They begin every spring cut down to 24" and grow to 6' by June. I keep around 2-3 in of mulch on the bed and every 3 yrs or so turn nutrient enriched garden soil into the bed. Last year for the 1st time they got a fungus, I treated it but wrestled with it all year, even cutting the plants back to 24" in July, they came back to 6' by Sept and got the fungus again. This year the leaves are completely spotted in yellow now and it was sudden. Not rust or fungus from what I can tell and they have no bugs I can see. If you're not aware we have had, last year and this, much flooding and so these have had way too much water but not sat in water (the bed they are in has not flooded). I am at a loss at what to do.

ANSWER: Dear Shary, I hope I can help you, but I understand your frustration.  I also lived in the Houston area for about 20 years, and I know what the weather has been like this year.  You evidently have a severe fungus on these altheas brought on by the extremely wet conditions lately.  You will need to spray the plants with a very strong fungicide.  They will need to be sprayed every week to 10 days thoroughly until the condition clears, and you will also need to remove all the fallen leaves from the area.  Do not mulch these.  Hold back on the fertilizer because in extreme conditions, it can accelerate these problems.  A lot of long established plantings are dying because of the extremely wet weather, and you may see more plants becoming ill with fungus.  Replacing the mulch with a drier medium might be very beneficial and keep the fungus under control.  You will know the fungus is leaving when new leaves grow without spots.  I hope you are able to save the plants.  Let me know if you have more questions.  Good luck, Melissa

---------- FOLLOW-UP ----------

QUESTION: Thank you so much Melissa.
I used a fungicide last year recommended by Maas Nursery (in case you know them, they are so awesome)and it may have worked but I did not remove anything on the ground so I will never know. Can you suggest any, I've never used fungicides before then. Asking because you say "very strong" and I don't have a clue how to tell.
In case it makes a difference, last year the spots were brown rusty color but this year they are bright yellow spots and the spots don't enlarge to make the whole leaf yellow, the leaf is just covered in the spots. Also when the new leaves come out they do not have any spots but develop them after a couple of weeks, even now while much of the tree is covered in the yellow spotted leaves. Last year the leaves dropped like crazy but right now they are staying on.
Should I cut them back when I treat or treat and leave as is?
Again thanks so much.

Dear Shary, For a strong fungicide, I prefer one containing either the active ingredient proprioconozole or chlorothalonil.  Fertilome makes a good one called Systemic Liquid Fungicide.  You'll have to mix it up and spray with a pump up sprayer.  I would definitely remove the mulch before spraying to get it out of the way as well as removing any fallen leaves.  You might cut the plants back also when you spray, but you can use your own best judgment on that.  Another thing that comes to mind is you might want to consider the wind flow in that area.  Does it get a lot of circulation, or have plants grown up nearby that cause poor circulation?  Just having a few plants grown up and branching out can drastically change the environment in another area.  Try to allow for as much air movement as possible and that should help.  I also wouldn't add more mulch until perhaps later in the summer when the plants hopefully will look much better.  Try to keep the area drier than usual, and make sure the leaves aren't getting wet when watering.  You should probably spray about three times a week apart to help the situation.  I do hope this helps your altheas.  They don't often have problems, but the extremely wet weather have made things very difficult.  Good luck, Melissa

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Melissa Johnston


Plant diseases, landscaping, tropical plants, roses, herbs, plant care, grafting, horticulture, plant identification, anything about plants I can likely answer.


35 years experience in various plant businesses, 1984 Certified Texas Master Gardener.

Master Gardener Association of Texas charter member

none as of yet, but I have a plant q&a book I am in process of submitting.

Magna cum laude graduate of Texas A&M, 1978

Awards and Honors
Plant growing awards, highest grade for Texas Master Gardener graduates.

Past/Present Clients
Past member of and was very highly rated. Owned landscape company in the past, Almost Paradise, and was very successful despite little equipment, no help, and no advertising. Lived well for two years until 9/11.

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