White fungus on hibiscus

Pink Hibiscus Mealybug 2.jpg

Pink hibiscus mealybugs are covered with a white, fuzzy material that looks like mold or fungus. (Dan Gill)

Question: I have a hibiscus growing in a pot that has bloomed very well this summer. Recently, the plant has stopped blooming and is showing yellow leaves. When I look at the plant closely, I see a fuzzy white mold or fungus growing on the tips of the branches. What is this and what should I do to help my hibiscus? – Nan Clark

Answer: This is not actually a fungal problem – these are insects called pink hibiscus mealybugs. The insects are covered with a white, fuzzy/powdery material. They cluster on the new growth and buds of hibiscus plants, and are very obvious when they are present. They feed by sucking out the sap of the bush. While feeding they inject toxic compounds that can seriously damage or even kill a plant.

Pink hibiscus mealybugs can be controlled organically with several applications of a light horticultural oil, such as Year Round Spray Oil, All Seasons Oil or Organocide. Or, you could use one of the pyrethroids (permethrin, bifenthrin, cyfluthrin or others). Imidacloprid, applied as a drench, can also be used to control pink hibiscus mealybugs, either alone or in conjunction with the insecticides already mentioned. Do not use Malathion on hibiscuses, as they are sensitive to this insecticide.


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Hibiscus Plant Care

There are small, bright white spots all over my hibiscus!

Mealybugs Look Like Spots of White Cotton

Mealybugs are not a common pest on hibiscus the way aphids are; however, from time to time these pests may show up on your hibiscus. If not controlled, they can rapidly spread to all your hibiscus (and other plants) where they suck juices and create a real mess as they excrete excess plant sugars onto the leaves. This “honeydew” is food for black mold which grows in it and discolors the leaves. Defoliation (loss of leaves) of the entire plant is often the result of all this stress.

What do Mealybugs Look Like?

You are most likely to notice mealybugs when they reach the adult stage and begin to cover themselves with a white, waxy, protective material that looks somewhat like cotton balls. This bright white color stands out against the green of the leaves. One difference that distinguishes mealybugs from other pests, such as snow scale, is that mealybugs can be found on both tops and bottoms of leaves, on flower buds, on the stem that holds the buds (the peduncle), or anywhere else on the plant. Once they cover themselves with the cottony mass they rarely move, continuing to feed on the plant in the same place. Mealybug young are called runners, and are more difficult to see. These are the bugs that spread from plant to plant. They are good climbers and can climb down to the ground and back up another plant. This is the stage of growth that is susceptible to chemical pest control sprays, but it is nearly impossible to spot mealybugs at this stage. Mealybug females lay egg masses on the plants or even on the sides of pots. These egg masses resemble the adults in that they are covered with the same waxy, white, protective material.

What do I do if I See Mealybugs?

Every White Spot is a Mealybug or Egg Mass

Once you spot mealybugs on your hibiscus or other plants, do not expect them to just go away. They probably won’t, although predatory insects will help control them in an outside garden. More than likely the mealybugs will spread to all of your garden plants unless you intervene. They can live and reproduce on weeds, which makes removing weeds near your hibiscus very important. The reason mealybugs are such a formidable pest is that the white waxy material they cover themselves and their eggs with is like an armor that protects them from normal pesticide sprays. When they are young they are not covered with the white waxy “cotton” and can be killed with sprays, which is helpful. But the protected adult females will continue to lay and protect eggs more rapidly than you can kill the young runners with pesticides. The result is that no matter how much you spray, your mealybug population will continue to spread out of control.

To eliminate a mealybug invasion, you need a 2-pronged response: a systemic pesticide and physical cleaning of the plant, since even a systemic pesticide works more slowly than mealybugs reproduce in many cases. An optional 3rd prong is adding beneficial insects to your garden at the end of the process to make sure any new mealybugs that may still survive are dispatched of quickly.


Step 1 ~ A Systemic Pesticide:

Start with a systemic pesticide – one that is absorbed through the roots of the hibiscus and remains present in the plant sap. When the mealybugs consume the sap they are eventually poisoned. Imidicloprid is the active ingredient that works best. It is found in Bayer Tree & Shrub available from us or from your favorite garden center. Using the heaviest of the recommended doses on the label for your plant or pot size, sprinkle the product onto the soil at the base of the plant, then water it just enough to dissolve the granules. Don’t water again until the potting soil or ground is fairly dry (but well before the plants wilt). Mealybugs are harder to kill this way than aphids or whiteflies, but eventually they will either leave the treated plants or die. You may have to make a second application if the first one does not make a significant difference within 3-4 weeks after applying it.


Step 2 ~ Physically Clean the Plant:

Mealybugs Lay Eggs on Sides and Under Rims of Pots

Once you have applied the systemic pesticide, you should physically clean away the existing, adult mealybugs. Since they don’t move and are easy to see, they are easy to remove. If you have only one or two infected plants, use Q-tips and rubbing alcohol. Just dip a Q-tip in the alcohol, then touch the mealybug with the alcohol. It will start to eat through the waxy armor and kill the mealybug. Use the Q-tip to wipe the mealybug off the plant completely, and deposit it into a plastic bag. It’s a slow process, but if you remove each adult mealybug and each egg deposit this way, along with the application of Bayer Tree & Shrub to kill any new mealybugs, you can control your infestation very quickly. You will need to check your plant over very thoroughly several times a week for a while and use Q-tips and alcohol to remove any new mealybug adults that appear.

If you have lots of hibiscus plants, the Q-tips and alcohol method is just not practical. For a large infestation on many plants, a new cleaning product called Limonene, if used in the right dosage, can be sprayed on large numbers of plants, and it will melt away the mealybug’s waxy coating, as well as the sugary honeydew and sooty mold. Limonene is made from the skin of citrus fruit – ours is made from orange peels – and is popular in many new household cleaners. For live plants, you need pure limonene and water, without any of the other harsh ingredients in household cleaning products. To get the strength of limonene right requires some experimentation: too strong a solution will cause the hibiscus to defoliate completely, and too weak will not melt the waxy coating. We are now offering Limonene for cleaning your plants that is mixed in water at the optimum strength. You spray it straight onto the mealybugs, and leave it on the plant to clean away the waxy coating and the mealybugs without you having to physically wipe them off. Be sure to use the limonene to clean your plant pots too – around all sides, under the rims, the ground under the pot, everywhere! Inspect your hibiscus several times a week, and spray any new mealybugs you see with the limonene until they completely disappear.


Optional Step 3 ~ Beneficial Insects:

An optional final prong of a 3-prong response to mealybugs is to purchase some predator insects that eat mealybugs. One that is widely available is the pretty garden ladybug. If the ladybugs stick around, they will eat mealybugs, aphids, and other common insect pests. The problem with such beneficial insects is that they will often fly away and not stick around to do the job. We consider them an optional, but potentially valuable way to combat mealybugs.


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

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.

The Hibiscus tree belongs to a group of flowering plants in the mallow family the Malvaceae.

It is local to warm temperate, subtropical and tropical countries like California, Texas, Florida and other tropical countries around the world.

Hibiscus leaves turning yellow is a common problem, but not one you should be too concerned with.

If your Hibiscus leaves turn yellow, it means your Hibiscus is trying to tell you it needs something.

Ask yourself these seven questions to determine just what the problem may be.

#1 – Is My Hibiscus Getting Enough Nourishment?

If your Hibiscus leaves are turning partly yellow but not falling off, this can be a signal your plant has a nutrient deficiency, experiencing iron chlorosis and needs a dose of fertilizer, epsom salts or a soil amendment.

#2 – Hibiscus Leaves Turning Yellow – Am I Watering Correctly?

Tropical hibiscus leaves may turn yellow if it takes lots of water, and they may turn yellow if you water too little.

Remember, Hibiscus plants need lots of water, even more so when it’s is a potted Hibiscus, windy or very hot.

Nevertheless, if you water too much, plants can experience problems with root rot.

The idea is to maintain a consistently moist soil around Hibiscus plants.

Be careful not to keep the soil too soggy.

During your tropical plant’s dormant period, you should avoid overwatering it.

Little water is enough to keep the soil from becoming completely dry because it may lead to wilting.

Always be sure to provide good drainage.

If your plant is not planted in well-draining soil or does not have good drainage holes in its container, the ground will be soggy.

It will cause yellow leaves and root system.

To ensure your plant is getting enough water, check the soil every day or two by poking your finger into the top inch or so.

The dirt should feel slightly moist, not wet.

When it begins to feel dry, it’s time to water. You may also wish to invest in a self-watering pot to provide consistent watering.

There are also many high tech aids like large self watering planters to help you keep track of your plants’ watering and fertilizing needs.

#3 – Am I Keeping My Hibiscus At The Right Temperature?

Hot weather can cause yellow Hibiscus leaf because plants need extra water during warm, dry weather.

If your plant is too dry, you will initially notice the leaves turning yellow and falling off.

If you don’t attend to its special watering needs in the summer heat, the entire plant will dry up and may die from heat stress.

Hibiscus tree is also not tolerant of freezing weather. When the weather turns cold, the leaves will turn yellow and fall.

Remember, Hibiscus plants are not frost hardy, so bring outdoor plants in when a freeze is expected.

Drafts can cause yellowing and leaf drop. Hibiscus planted outdoors should be sheltered from the wind.

Hibiscus kept as houseplants should be protecting from drafts.

#4 – Is Your Hibiscus Getting The Right Amount Of Light?

Just as with water, too much or too little, only enough light can cause Hibiscus new leaves to turn yellow.

Excessive sunlight results in leaf sunburn which manifests as white spots on the leaves.

If this happens, you should prune off the damaged leaves and move your plant to a location where it can get partial shade during the hottest part of the day.

Too little light can also cause discoloration and falling leaves.

If this is the case, you’ll need to move your plant to a setting where it can get ample full sun.

#5 – Is it Time For My Plant To Go Dormant?

The Hibiscus’ growing season is spring, summer, and fall.

At the end of the autumn, yellowing leaves will fall.

This means your plant wants to go dormant, so you should reduce the amount you are watering and allow your plant to take a rest.

#6 – Is My Hibiscus In The Right Place?

During your plant’s period of dormancy, bring it into the house and keep it in a cool and dark area for about two months.

The environmental changes may affect hibiscus.

Toward the end of the dormancy season, cut the plant back and put it in a bright, sunny window.

Begin regular watering, and soon you’ll see new growth appear.

When this happens, start fertilizing your Hibiscus.

In the springtime, take your plant outdoors if you wish.

Moving plants from indoors to outdoors may cause leaf yellowing, cessation of blooming, and a wilted appearance.

These are all signs of stress.

To minimize this, transition your plant gradually from indoors to outdoors at the beginning of the growing season.

#7 – Are Pests Attacking My Hibiscus?

If leaves turn yellow and take on a mottled appearance with signs of injury on the undersides of the leaves, it is because of the infestation of spider mites.

Learn more about Spider Mites on Hibiscus Plants

To eradicate these pests, spray the entire plant with a solution of soapy water.

A couple of cups of plain water with a teaspoonful of Dr. Bronner’s liquid Castile soap should make short work of soft-bodied insects such as spider mites and aphids.

Spray the entire plant daily until the pests disappear.

Following this, give your plant a good rinse to remove soapy residue.

Source: hiddenvalleyhibiscus.com

3. Too Hot or Too Cold

The weather can lead to stress on your hibiscus plants. Ultimately, the weather does lead down to water as well. On those scorching, summer days, your plant is more stressed and needs an abundance of water to keep those huge leaves green.

Temperatures above 90 degrees can lead to stress. When they don’t have enough, they turn the leaves yellow, so they don’t require enough water.

Likewise, weather that is too cold can lead to problems. Remember, hibiscus plants are a tropical plant. They don’t handle freezing temperatures, below 38 degrees F, very well. They excel in temperatures 65-85 degrees F. When a hibiscus plant is too cold, they will turn their leaves yellow.

4. Sunlight

All plants need the proper amount of sunlight. Hibiscus plants do love sunlight, but they require moderate amounts. If you place your plant in an area that receives all day sun, their leaves will turn yellow or develop white spots. You can think of the white spots like a sunburn. Don’t worry; they won’t die because of the white spots, and it doesn’t indicate death.

Sunlight is the life source for all plants. If they don’t receive enough sunlight, they will drop some of their leaves, leaving less to support. It is your job to place the hibiscus plants in an area that receives a few hours of uninterrupted sunlight each day but still get shade.

It also could be a sign that your plant is ready to go dormant. Since they are tropical plants, winter is when they typically go dormant. If the yellow leaves coincide with the normal dormancy, allow the plan to enter its stage naturally. Bring it inside for the winter. When you bring your plant indoors, you can expect a moderate amount of yellow leaves. If all the leaves are off but the branches are pliable, it is in full dormancy.

5. Annoying Insects

Certain insects, especially spider mites, cause problems for hibiscus plants. If you notice the mottling of the leaves, it is time to check for spider mites. The leaves will look dirty and tired, with marks on the underside. Slowly, the leaves will turn yellow and fall off. Spider mites can destroy every leaf on your plant, so you need to treat them! It takes a few weeks for your plant to recover.

White Spots On Hibiscus – Knowledgebase Question

The white patches may be a fungus, brought about by less than perfect growing conditions, or they may be evidence that your plant has an infestation of mealy bugs. Try looking at the patches with a magnifying glass to see if you can tell whether the patch is a collection of little insects with cottony coatings, or just a single blotch of hairy fungus. Mealy bugs can be very difficult to control, and the first course of action is to try to remove them with a cotton swab dipped in plain water or rubbing alcohol. Or, try prying them off with a blunt knife. (You won’t do any more damage to your plant than the insects are already doing.) This may leave scars that will callous over, but it will help you save your plant. As a last resort, you may have to use an insecticide to rid your cactus of the pests. Mealy bugs travel very slowly, but they can leave eggs on all kinds of surfaces. Move your hibiscus away from other plants, and be sure to wipe down the sides of the pots to get rid of any eggs.
For continued good health, keep your plant in the sunniest spot you have. Keep it out of drafts and keep the humidity around it high if possible. Expect some yellowing of leaves in protest of the move. Reduce watering and fertilizing as the plant’s growth slows. Good luck with your plant!

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Wednesday – August 06, 2008

From: Wichita Falls, TX
Region: Southwest
Topic: Non-Natives, Pests, Edible Plants
Title: White spots on Hibiscus leaves
Answered by: Barbara Medford


My hibiscus trees have white spots or splotches on the leaves. What is it and what can I do to get rid of it? Also, the birds are eating my tomatoes faster than i can grow them. I’ve used the owl & snake tricks which work about a week & then they’re back eating again. What do you suggest?


Again, we have to figure out what plant we are talking about. There are literally hundreds of plants typically referred to as “hibiscus”, some annual, some perennial. There are some native hibiscus and many that are non-native, but all belong to the mallow family, so hopefully even if we pick the wrong one to discuss, the same advice will apply. Since you refer to hibiscus “trees” we believe that what you have is a Hibiscus syriacus, native to Asia, and often called Rose of Sharon. There are other mallows called Rose of Sharon, as well, adding to the confusion. A synonym to the current name is Althea syriacus, and lots of people have what they call altheas.

Since the Hibiscus syriacus is non-native to North America, we have no information on it in our Native Plant Database. At the Lady Bird Johnson Wildflower Center, we urge the use of plants native to the area in which they are being used, because they are already adapted to the environmental conditions there and thus will require less fertilizer, water and maintenance. However, we have done some research and will try to answer your questions on the leaf spot. This USDA Forest Service website on Rose of Sharon will give you general information on care for the plant as well as pests and diseases. It is hardy in Zones 5 to 8, and Wichita Falls is in Zone 8, according to the USDA Zone Hardiness Map.

Aphids may cover leaves with sticky honeydew. Over-fertilizing increases aphid infestation. However, we believe what you are asking about is bacterial leaf spot; the only treatment we found for that was to pick off and destroy the infected leaves. Don’t leave fallen leaves or blooms on the ground as they may harbor the bacteria.

Now, on to your tomato question. Once more, we are talking non-native plant. Most food plants are either non-native to North America or so intensively hybridized that they bear little resemblance to the original form. Tomato, Solanum lycopersicum, is a member of the Solaneaceae or Nightshade family, closely related to tobacco, chili peppers, potao and eggplant. It is native to Central and South America from Mexico to Argentina. With reference to keeping birds out of them, if we could devise a fool-proof method to keep all the little beasties that love tomatoes, too, off of them we would be zillionaires. See this excellent Texas A&M Horticulture site on Tomato Questions. One which addresses your question is quoted below:

“Tomatoes should be supported. Whether you cage or stake them is personal preference. Regardless of the method, plants with foliage and fruit supported off the ground will produce more than unsupported plants. Caging has several advantages. It involves less work than staking. Once the cage is placed over the plant there is no further manipulation of the plant – – no pruning, no tying. The fruit are simply harvested as they ripen. In many areas, staking and pruning of the plant to a single or multiple stem results in sunburn when the developing fruit is exposed to excessive sunlight. Other advantages of caging over staking include protection of fruit from bird damage by more vigorous foliage cover and less fruit rot. Caged tomato vines produce more fruit of a smaller size, but staked and tied plants produce less fruit which mature earlier yet are larger.”

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Q. My indoor hibiscus plant leaves are yellow, sticky and dropping, while the stems have small fuzzy white patches. What is causing this?

–Bob Brown, Gurnee

A. From the symptoms you describe, most likely the problem with your hibiscus is caused by mealybugs, a common pest of indoor plants. They suck the plant’s sap and excrete “honeydew,” which is the sticky substance you see. Leaves turn yellow and drop due to a general weakening of the plant by the feeding of the pests.

Mealybugs are protected by a white cottonlike covering, which can make them difficult to eradicate. If the plant is heavily infested, isolate it from other plants. Rinse the plant with a hard blast of water. If this doesn’t help, spray with an insecticidal soap every 7 to 10 days, following label directions.

You also can wipe off the plant with a soft cloth to remove mealybug clusters. Since this is a houseplant, it’s best not to use a chemical control. Consider discarding the plant and replacing it with a healthy plant in spring. Always inspect plants before you bring them indoors to avoid pest infestations.

Q. Is it possible to save forced indoor bulbs and plant them outdoors?

–Joan Duerig, Northbrook

A. Truly hardy forced bulbs may be saved with some effort, but don’t bother saving any non-hardy types, like paperwhite narcissus, or those that were forced in water. Forcing bulbs to bloom indoors is stressful and weakens the bulbs.

Hardy daffodil (narcissus) bulbs have the best return rate, while tulips are the more questionable and may not regain enough strength to flower again. It will take two to three years for some bulbs to bloom again after planting outdoors.

While the bulbs are blooming, keep the plant in bright light and evenly moist. Fertilize after it is finished blooming with a balanced formula. Remove spent blooms to prevent bulbs from setting seed.

It is important to leave any green foliage attached to the bulb since it helps manufacture food for the bulb, rejuvenating it for the next flowering period.

When the foliage is completely brown, dry and pulls away from the bulb, it is fully dormant.

Store it in a cool dark dry area (a cool basement would work) and replant in spring at least 2 to 3 inches deep for a narcissus.

Q. I planted Canadian hemlock trees this fall. They are turning brown at the top. Any ideas on what could be the problem?

–Michael Weber, Arlington Heights

A. Canadian hemlock (Tsuga canadensis) is best planted in spring because it is sensitive. The browning at the top of the tree is an indication of the overall health of your tree, especially the roots. Hemlocks are susceptible to root rot, which is what this sounds like.

Hemlock’s need well-drained, but evenly moist soil. If you overwatered or have poorly drained soils (combined with last year’s wet fall), the problem might be too much water in the soil. This suffocates the roots, causing them to rot and die.

There may not be anything you can do at this point if the plant has root rot. You may have to replace the tree in spring. If this is a low spot, improve the drainage by adding organic matter in spring and in fall.

Nancy Clifton writes for the Chicago Botanic Garden in Glencoe. Send e-mail to home&[email protected]

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