Hibiscus Has White Fungus – How To Get Rid Of Powdery Mildew On Hibiscus Plants

Hibiscus Has White Fungus – How To Get Rid Of Powdery Mildew On Hibiscus Plants

By: Mary H. Dyer, Credentialed Garden Writer

My hibiscus has white fungus; what should I do? White powdery mildew on hibiscus is a common problem that usually won’t kill the plant, but the powdery substance can definitely detract from its lush appearance. If you own a hibiscus with powdery mildew, all is not lost. Read on to find out more.

Symptoms of Hibiscus with Powdery Mildew

Powdery mildew begins as white spots that turn gray or tan as the fungus grows and covers more of the foliage. The fungus causes stunted growth and in severe cases, the leaves may wither and fall off the plant.

Powdery Mildew Treatment on Hibiscus

If a hibiscus has white fungus, it’s important to tackle the problem as soon as possible; once the problem is established, it becomes more difficult to control. There are several possible treatments, but chemical fungicides, which are toxic and aren’t always effective, it should always be a last resort.

How to Get Rid of Powdery Mildew: Cultural Controls

  • Keep your hibiscus healthy, as strong plants are able to withstand powdery mildew better than weak, stressed plants.
  • Water your hibiscus at the base of the plants and not on the leaves. Morning is the best time to water because the leaves will have plenty of time to dry.
  • Avoid high-nitrogen fertilizers, as lush, new growth is more prone to disease. Don’t fertilize hibiscus when powdery mildew is present.
  • Be sure hibiscus plants aren’t crowded since fungal diseases thrive in warm, humid conditions with poor air circulation. If the shrubs are crowded, consider transplanting them to a space where they have more room to breathe.
  • Trim affected growth immediately. Dispose of diseased plant material carefully, and never place it on the compost pile.

Powdery Mildew Treatment on Hibiscus: Fungicide Sprays

  • Neem oil – A mixture of Neem oil and water is a safe, organic solution for powdery mildew. Mix the spray at a rate of 2 tablespoons (15 ml) Neem oil to 1 gallon (4 L) of water. Use a pump sprayer to apply the solution every week until the mildew is no longer visible. Some gardeners like to add a teaspoon of liquid dish soap to the Neem oil solution.
  • Baking soda – You can also try an organic spray consisting of a teaspoon of baking soda, a few drops of vegetable oil and a quart of water. Spray the mixture on affected leaves.
  • Commercial sprays – Although a number of chemical fungicides are available, many gardeners prefer to use products containing sulfur or copper every seven to 14 days, or as recommended on the product label. Fungicides are generally effective only early in the season. Once powdery mildew is established, fungicides tend to be ineffective and usually aren’t recommended.

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The name “powdery mildew” is self-explanatory. It is a common type of fungus issue. It works in a series of Erysiphales. So there are more than hundreds of species of fungi in this series. It causes a white or gray form of powdery film on various parts of the plants.

The powdery film consists of mycelia and spores in general. But the taxonomy of Erysiphales series is different now. In 2000s, scientists have discovered a new DNA pattern of this fungus disease. So it can be anything among the hundreds of species of fungi.

The reproduction process of powdery mildew is simple as well. It works both asexually and sexually. The asexual stage spread this disease using spores. The Chasmothecia generates fruiting bodies in sexual stage. Scientists have also found Podosphaera and Golovinomyces that attack roses and cucurbits respectively.

Sooty Mold

Sooty mold on shrub holly.

Symptoms: Black coating on upper side of leaves. It may appear as a dark haze, or be thick enough to turn the leaves entirely black. It has a dry appearance, not slimy or sticky. It may appear on the top growth or the lower growth of the affected plant. It can appear on any plant.

Scale infestation that caused sooty mold on the leaves beneath them.

Caused by: Sooty mold is a fungus that grows on “honeydew”, the excrement of insects like scale, aphids, whitefly and mealybug. For some cryptic insects like scales, sooty mold may be the first indication that there is an infestation.

Impact: Mostly cosmetic, as the fungus does not invade plant tissues or cause direct damage. However, the coating can restrict sunlight from reaching the leaf and reduce the ability to photosynthesize. This is generally only a problem for already weakened or sick plants.

Treatment: Look at plants above the affected plant if sooty mold is found on the upper part of the plant, or at the upper growth of the same plant if affected leaves are at the bottom. You will undoubtedly find an infestation of one of the insects mentioned above. Treat the insect problem and the mildew growth will stop. (Specific treatment will be determined by type of insect found.) The mold itself is difficult to remove and usually needs to be left to weather off naturally, or be covered by new growth.

Why Powdery Mildew is a Disaster on Buds During and After Harvest

Powdery mildew is a catastrophe to have on your marijuana buds at any time, but especially when you are starting a harvest. The very act of harvesting will spread the spores to any uninfected plants. And once it’s on the buds at harvest, there’s not much you can do to save your crop. You can try very carefully to remove the infected plants from the area. The problem is that every time you touch a plant that’s infected, you can spread the microscopic spores through the air to nearby plants. If the infestation has not spread too far, you can try to very carefully cut out the infected leaves and buds and place them in plastic bags for disposal. You will need to watch your plants closely to make sure you’ve stopped the disease during flowering, too. If you see it has spread to other plants, even after you’ve cut and removed the infected leaves and buds, there’s little you can do but keep cutting and removing. Unfortunately, this is a recipe for heavy damages or totally destroyed crop. The other danger is that you’ve harvested infected buds and unintentionally mixed them in with the remaining good buds during the harvesting process. Naturally, the powdery mildew will continue to spread to other buds even after harvest.

One unwelcome visitor to my garden at this time of year is powdery mildew. Here’s how to control this plant disease with natural remedies, including a homemade baking soda spray treatment.

Signs of Powdery Mildew

It starts as white patches on the leaves of squash, lilacs, phlox, bee balm, and other plants, making them look like they have been dusted with baby powder. Early on it wipes off or washes away only to return again.

Eventually the affected leaves turn yellow and die on many plants while others continue to soldier on.

So far this year only our squash have been affected.

There is no sign of it on other susceptible plants such as phlox.

Causes of Powdery Mildew

This is probably due to the fact that it is not caused by just one fungus but by several different species that are attracted to different kinds of plants. The powdery mildew that you find on your squash is not the same as the mildew on your beans or roses. Cucurbits such as pumpkins, squash, cukes, and melons have three different powdery mildew fungi gunning for them that can thrive in both humid and dry weather. The spores of the fungi are windborne and can’t be avoided. No wonder the squash get hit every year!

Remedies for Powdery Mildew

There are lots of home remedies but researchers have found that simply spraying with plain water weekly can be effective. The spores like humidity but hate rain and water. They can’t germinate or grow if the leaves are wet. This is the opposite of what most gardeners think, me included.

One season I tried to defeat powdery mildew by planting squash in our high tunnel, thinking that if I could keep the leaves dry they would not be affected. Naturally they got the worst case of powdery mildew I have ever seen! It was the perfect place for it to thrive - high humidity and no rain hitting the leaves. Another lesson learned the hard way!

If you decide to try a home remedy rather than plain water there are several that have been proven to be effective if used early. They can slow or stop the spread early on but once the fungi are established in the leaves, they won’t eliminate it.

Homemade Baking Soda Spray

Many of these remedies include baking soda. Just be aware that baking soda can burn plants and it can build up in your soil and cause deficiencies in calcium, magnesium, and iron. Potassium bicarbonate can be substituted for baking soda. Test these sprays on a small area first to make sure they do not damage your plants.

  • Mix 1 tablespoon baking soda with 1 tablespoon vegetable oil and 1 teaspoon dish soap in 1 gallon of water.
  • Mix 4 tablespoons baking soda with 2 tablespoons of Murphy’s oil soap in 1 gallon of water.
  • Mix 2 to 3 tablespoons vinegar with 1 gallon of water. Be sure to test this first because vinegar can burn plants.
  • Neem is an organic fungicide. Follow instructions on the label.
  • Mix 1 part milk with 10 parts water.
  • Some folks swear by mouthwash as an effective fungicide but it is not organic. They recommend 1 cup mouthwash to 3 cups of water.

To keep the fungi from developing a resistance to your homemade spray it is recommended that you alternate remedies each week. Use baking soda one week and milk the next. Whether spraying with water or a home remedy, do it early in the day so the leaves can have a chance to dry before evening.

When adding new plants to your flower beds look for mildew resistant varieties. Don’t over-fertilize with high nitrogen fertilizers since soft new growth is very susceptible to infection. Space plants far enough apart to promote good air circulation. If infection starts in lower leaves, snip them off. Make sure plants get enough direct sunlight. Prevention is the best medicine!

Reader Comments

Garlic rot

Submitted by Janice on July 1, 2020 - 11:02am

What can u do to stop moody garlic and is it safe to eat? What about planting next year?

Powdery mildew

Submitted by DON W on November 24, 2019 - 3:02pm

I have found that a mixture of 3% hydrogen peroxide with insecticidal soap works very well at controlling both powdery mildew and insect pests. I buy 27% h2o2 at the local farm supply and dilute it 1 quart to 9 quarts water, and add the insecticidal soap in my backpack sprayer. I spray all my fruit trees at the first hint of the fungus, and this keeps the trees happy for several weeks. I too am in the PNW.

Dwarf Japanese maple

Submitted by Brian on August 20, 2019 - 9:47pm

My Japanese Maple looks like it has this powdery mildew. I sprayed a few leaves with some “seven”, hope I didn’t kill it more. A week or so back I noticed something odd, went on vacation and now it has spread quite a lot. I read here that all infected leaves should be removed and destroyed. yikes. Will the other options (Milk & water or baking soda) work without removing the infected parts?

Powdery midew remedies

Submitted by sonya Norton on July 19, 2019 - 4:47pm

Bicarb works, but I'm never sure if i overdid it. I'm a firm believer in milk and water as a spray. It doesn't seem to matter of it's skimmed milk or whole milk. 50/50 with water, weekly or after rain. Has even beaten the mildew on lupins, my worst sufferer here in the PNW.

BlackBerry plants

Submitted by Marie on July 20, 2019 - 11:57pm

The stink bugs have destroyed majority of my blackberry bushes/plants. Help how do I prevent this for next years crop.

Powdery mildew

Submitted by richard h hoyt on July 4, 2019 - 12:46pm

Implement Lactobacillus Serum as a preventive and you won't get PM. Google search on how to make. Really simple.

Lactobacillus Serum

Submitted by Payton Jett on July 31, 2019 - 10:28pm

Once I make this, how do I implement?

How to make lactobacillus serum

Submitted by Annie Herbert on October 5, 2019 - 4:44am

Will I have to dig up new plants .honey suckle .

Crystals on my rose-scented geranium?

Submitted by Sian on June 22, 2019 - 2:42pm

Hey, there! I just noticed a peculiar thing I've never seen before three leaves of my rose-scented geranium have what appears to be salt in their gullies. I thought at first I was looking at powdery mildew (a familiar foe), until I noticed the loose, sparkling quality of the substance. Are the leaves leaching salt? I do not fertilize, never need to, and the effected leaves still look as healthy as ever (I have still removed them in case the substance is otherwise nefarious). What could this be? For information's sake, this geranium is planted in a half-gallon SmartPot.

Powdery Mildew

Submitted by Ron Lane on June 7, 2019 - 1:45pm

This is one of the better PM articles I have seen on the net. One correction is that baking soda does not stop powdery mildew, it only helps to prevent it. You may spray it on and think your PM is gone, but if you come back in a couple of hours your PM has returned.
Pristine is a BASF product that actually eliminates PM. Some form of it might be available to homeowners. Of the softer chemistries, Circadian Sunrise is the only one I've seen that consistently stops PM cold. The problem with that product is that the smallest unit presently sold is a 2.5 lb concentrate, which is far more product than most homeowner will use in their gardens over the course of a year or more.

White power on leaves

Submitted by Anna on November 1, 2018 - 8:51pm

I have white powdery substance on my zinnias. Will this make the seeds in the flowers be bad for next year?

Yes, the mother plant has

Submitted by dave on November 16, 2018 - 3:40pm

Yes, the mother plant has been infected and will pass along those genetics to the seedlings which will also carry the disease.

That's not how genetics works

Submitted by Marc on June 11, 2019 - 9:27am

That's not how genetics works, Dave.

Powdery mildew on bee balm

Submitted by fredric lacarbonara on October 8, 2018 - 1:52pm

the info I have is to spray with milk/water mix or baking soda/water mix. I am doing that , but is it a one time treatment or multiple treatments. please advise how many times and how often to spray. ty

Powdery Mildew Treatment

Submitted by The Editors on October 9, 2018 - 4:13pm

It will likely require multiple treatments to keep the fungus at bay. Test the mixture on one plant first, waiting at least 24 hours to be sure that there are no negative effects. Then spray all affected plants at least once a week. After three or four applications, wait to see if symptoms return before spraying again.

White powder fungus

Submitted by Lisa in Texas on October 5, 2018 - 10:39pm

I have been fighting this in my house for almost 4 years. I have tossed out so many plants I can’t tell you how much money its cost. I am wondering if two giant chinese evergreens are causing it - the have never had it at least not visibly. I am ready to torch the house or at least throw away every plant I have and fumigate / steam clean every nook and cranny including AC ducts. I am at my wits end.

White powdery mildew hay spread to much cherry tree

Submitted by Jack G. on November 13, 2017 - 8:59pm

I'm just sick, I just got 2 new cherry trees 1 Bing, 1 Black Tartarian cherry tree and I spread hay down first before I mulched around the bottom of the trees. The hay I used has white powdery looking stuff in the middle of it, not knowing I put it down and put mulch on top of it. It is Nov 13th here in Wisconsin and cold out. Does the hay have white powdery mildew and will this now infest the trees next spring? Should I dig up all of the mulch and get rid of it all? What should I do?

Late reply but worth mentioning I thing.

Submitted by Rocky on February 14, 2019 - 8:24pm

Jack everything you're describing to me sounds like the hay possibly has mycelium growing on it and while PWM is a fungal culture Mycelium in and of itself can be very very beneficial to plants/trees.
The Mycelium will grow throughout the same substrate the roots also colonize and create a symbiotic relationship with the roots themselves, while mycelium itself is started with other mediums hay is a much loved substrate to colonize after the mycelium has been birthed.
By using a layer of hay beneath your trees you've given the mycelium that was either spores lying dormant in wait or living mycelium beneath the hay previously a nice secondary substrate to grow through before expanding into the substrate your roots have begun colonizing.
I'm not going to pretend to know all the names of the different ways the relationship is symbiotic but I have recently been researching this topic a lot and can say for sure it's not just beneficial for one or 2 little things. I can't say that every strain of mycelium is going to be equally as beneficial obviously or even beneficial at all, some fungus (mycelium fruits fungus/mushrooms) like PWM use the plants themselves for hosts as mycelium itself does actually consume food rather than absorb nutrients through roots like plants but only certain types are threats to plants/trees.
Chances are the Mycelium you seen on the hay would take a very very long time (many seasons) to reach the top layer but if it does it could very well start fruiting some mushrooms annually if that's the type of mycelium you seen (not all types produce mushrooms of course). Many strains of mycelium have a natural fruiting time in Oct./ Nov. and also really thrives at that time of year so it makes sense for the time of year you seen it, which is another part of what you said that makes me feel it wasn't PWM at all.

"I spread hay down first before I mulched around the bottom of the trees. The hay I used has white powdery looking stuff in the middle of it, not knowing I put it down and put mulch on top of it. It is Nov 13th here in Wisconsin and cold out"

PWM wouldn't be living on hay at that time of year outside but mycelium definitely could! Laying down mulch on top of the hay is an interesting touch as many beneficial mycelium species really love wood as well!
Anyways I know my reply is very late but hope you still find some useful information here and if you enjoy gardening at any level I highly recommend further investigating yourself as mycology is a very interesting hobby to get into.

Powdery mildew

Submitted by Linda Schwin on July 28, 2017 - 8:14am

I have powdery mildew on my peonies. I sprayed with neem oil but now the plants look dry and damaged. Should I cut the plants all the way down? Will they come back next year if I do? Is there anything I can add to the soil? This is the second year this has happened to these plants. Last year I did not treat them with anything.

How to keep mildew of peonies plant

Submitted by Simon viola on June 18, 2018 - 8:06pm

Every year after the season I start getting fungus on my peonies what can I use to prevent this.

PM on peonies

Submitted by The Editors on August 27, 2018 - 11:29am

Are your peonies crowded? You might try thinning them out, per above to improve circulation: Selectively prune overcrowded areas to increase air circulation this also helps to reduce humidity around your plants.

You could also try the spray solution listed above:

  • Mix 1 teaspoon baking soda in 1 quart of water. Spray plants thoroughly, as the solution will only kill fungus that it comes into contact with.

Powdery mildew

Submitted by Ken Diehn on July 20, 2017 - 10:10pm

You mention to destroy plants and not compost. What method is best? Will burning cause the mildew spread to other plant? How about other diseases on plants, will burning spread disease?

Burning powdery mildew

Submitted by Cindy on October 22, 2017 - 2:33pm

Did you ever find if powdery mildew is spread by burning infected plants?

Burning Powdery Mildew

Submitted by Oliver on October 18, 2018 - 7:59pm

I have been doing a lot of research on powdery mildew. Temperatures above 90 degrees kill it.

Grape Vine

Submitted by Peter on July 20, 2017 - 11:11am

Our concord grape vine seems to have "expired", after 5 years of fairly reliable fruity growth. How can I tell if I need to start over, or find some "life" in what remains? Sad. The neighboring vines are doing well.

Rosebush fungus ?

Submitted by Dev Prashad on June 12, 2017 - 9:17pm

Would like to know what some white fuzzy looking stuff on the rosebuds might be and
what can be done to eliminate it.
Looks like the fuzz n peaches but is a bright white in colour

Powdery mildew on roses

Submitted by The Editors on June 13, 2017 - 1:48pm

It sounds like powdery mildew. See guidance above and

• plant roses in full sunlight.

• space plants to allow ample air circulation

• fertilize to maintain vigor but do not overfertilize

• avoid wetting leaves when watering use drip irrigation, if possible

• prune affected canes and collect and destroy cuttings (do not compost)

• in future, select rose varieties that are resistant

Sounds more like aphids to me

Submitted by Cass on June 5, 2019 - 9:25am

Sounds more like aphids to me. Roses are certainly prone to white mealy bugs. The “bright white” is what convinced me. Mildew isn’t typically bright white but the infuriating little critters definitely are.
If it’s them, alcohol will kill them only if it actually touches them. Neem will repel them. Most commercial pesticides are useless thanks to the typical resistance. I knock them off using water pressure and then use Neem to keep them off. Repeat as needed, at least 3 times since they’ll also dig into the soil plus you’re dealing with the juveniles and eggs.
If it’s a small houseplant I’ll pick them off or kill them individually with isopropyl alcohol. Again, retreat as necessary and keep in quarantine. The awful things can lie in wait without a plant to feed on for a long time so be careful about the site and disinfect.

Powdery Mildew and Environmental parameter

Submitted by Pawar Bhalchandra on October 27, 2016 - 12:04pm

Would like know about relationship between disease powdery mildew and environmental factors specifically Temperature, Relative Humidity, Rain Fall and Wind speed. Is there any quantitative MODEL which defines relationship amongs them in control of disease.

Red Spider Mite on hydrangeas

Submitted by Alison on October 16, 2016 - 2:42am

Can you tell me what to spray to rid the plant from this pest. It has spread to other plants in the area.

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