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Black Spots on Plumeria (Causes and Treatment)

Plumeria plant leaves showing black spot symptoms

You can enjoy a relaxing and serene environment within your sweet home if you have plumeria growing indoors. So it’s undoubtedly disheartening when you see your plant having black spots. 

The first instinct that you have in mind is to discard the plant since you might think that the plant is already dying, but hold on! 

You might want to pause for a moment and thoroughly identify the cause of black spots. You’ll be surprised that there are effective ways of bringing your plant back to its thriving state.

Plumeria black spots occur due to  fungal diseases like frangipani rust, black tip fungus or scooty mold. In addition, leaf spot disease and insect infestation are the most common reasons for black spots on plumeria. Environmental factors like low humidity, scorching can also cause this problem.

What Causes Black Spots on Plumeria Leaves

There are many possible reasons why your Plumeria is having black spots on its leaves, and it’s important to identify the main causes to apply the appropriate treatment that your plant needs.

Here are some of the factors that affect your Plumeria from having black spots.

Frangipani Rust

Frangipani rust, also known as Plumeria rust, is caused by Coleosporium Plumeriae, a fungus that commonly travels through air and lands on the leaves of your plant. 

The early symptoms of Frangipani rust show hundreds of visible yellow-orange spores underneath the leaves. Those spores can be easily removed by shaking or rubbing the leaves of Plumeria.

As the disease continues the invasion, you will see that the upper portion of the leaves will indicate yellow spots opposite to the dots underneath. Later on, those yellow spots will turn grayish and eventually become necrotic black spots.  

Your Plumeria leaves will also experience drying, curling, and withering, indicating that it urgently needs your help.

How to Treat:

  • If you assess that your Plumeria is suffering from Frangipani Rust, consider isolating your plant first to avoid the possible transfer of fungal infestation.
  • Then cut off all infected leaves using a pair of shears to immediately stop the spread of the disease. In trimming, make sure not to drop the infected leaves on the healthy ones, or else the spores will transfer.
  • Throw off all infected parts straight to your garbage area, disinfect your tools, and wash your hands properly before going back to your plant.
  • While moving your plant, make sure that it will receive an adequate amount of sunlight, preferably 5-6 hours of full sunlight. 
  • Wash the remaining leaves with a surge of water, just in case some spores survived the elimination process. Apparently, if you notice that soil is dry, you can water your plant as well.
  • After ensuring that your plant leaves are already spore-free, spray fungicide to prevent recurring infection.
  • Make sure that you remove all excess water from your pot saucer. 

Black Tip Fungus

Though the leading cause of this disease is fungi infestation, you’ll be surprised that ants help occur the fungal infestation. Here’s how:

Ants are attracted to the sweet honeydew excreted by aphids and some other insects. They collect it and store it on holes they have created on the tip of your Plumeria.

Because of the humidity build-up inside the hole, it will eventually become a nesting ground for fungi.

This disease causes noticeable black molds on the tips of your Plumeria, and if you do not treat it, it will soon spread out and infect the stems of the plant. Once the infection spread like wildfire, it will be harder for you to control the disease.

Though it rarely kills your plant, a recurring scenario of blacktip will deplete your plant’s stamina. Consequently, you will be disappointed with your Plumeria failing bloom.

How to Treat:

  • Since black tip fungus loves a humid environment, it’s highly recommended that you relocate the Plumeria to a warm environment. Preferably in a table beside the window so it can absorb enough sunlight, reducing humidity.
  • Spray fungicide right to where the black spots are. Continue spraying every other day until you get control of the situation. Slowly reduce the frequency of spraying when your Plumeria starts to recover.
  • Spray seaweed extract liquid fertilizer on the tip of your Plumeria or damp cotton soaked in hydrogen peroxide to reduce the darkening of the tip.
  • Make sure to reduce watering frequency when the winter season starts.
  • If the blackening of the tip continues to spread, trim off your plant to prevent further damage. Don’t get frustrated. It will eventually grow back after winter.

Sooty mold

Though sooty mold is a common problem on garden shrubs, your Plumeria is not exempted from experiencing this problem.

Generally, sooty mold is caused by fungi that develop from honeydews that sap-sucking insects, such as mealybugs and aphids, excreted on your Plumeria.

Sooty mold does not directly damage your plant, but the thick coating that it produces blocks sunlight which is essential for plants to perform Photosynthesis. Because of that, your Plumeria leaves will slowly darken, and your plant’s growth will deteriorate.

You will most likely see some visible symptoms, such as a black-powdered coating on your plant leaves and some of its twigs. If you happen to wipe off the powder coating, you will also see some dark brown spots on your plant leaves.

How to Treat:

  • Technically, if you control the sap-sucking insects within your plant, you can definitely prevent a further breakout of sooty mold. Rub your Plumeria leaves with cotton soaked in alcohol since this is an effective way to eliminate sap-sucking insects.
  • This might sound weird, but shoving away the ants in your Plumeria is effective since ants are capable of protecting the sap-sucking insects from their natural predators like wasps and beetles. Sprinkle some cinnamon powder around your plant to shove ants away.
  • In removing the mold, spray your plant leaves with a liquid detergent solution. Just mix 1 tablespoon of liquid detergent in a gallon of water. Wait for 15-20 minutes, then rinse it off with water. Repeat the process every other day until the molds turn dry and flake off the leaves. 
  • There’s a low possibility that sooty mold will recur once you eliminate the presence of sap-sucking insects.

Stem Rot

Stem rot is caused by a pathogen called Phytophthora. It is a soil-borne fungus that thrives in a moist environment.

Upon closer look, you will see that your Plumeria’s stem is turning black, which usually extends up to your plant’s roots. Aside from that, you will notice that leaves are turning yellow and are starting to wilt.

Also, if you remove your Plumeria from the pot, you will see that the roots are starting to show discoloration and already becoming mushy.

How to Treat:

  • If you suspect that your Plumeria is experiencing stem rot, immediately isolate it from other houseplants. Place it in a warm, low humid environment, by this way, you are slowing down the development process of the pathogens.
  • Gently remove the plant from the pot and thoroughly wash the roots. Cut off all infected parts to prevent further damage to your Plumeria. If you can still see some healthy white roots and the stems are not fully damaged yet, then there’s a big possibility that your plant might survive. Otherwise, if all roots are infected, then repotting is not advisable, thus you need to consider propagating your Plumeria.
  • If there are still healthy roots that can be planted, make sure that you thoroughly wash them. Since you trim off the roots, you also need to prune the leaves of your Plumeria. The volume of the leaves should match the roots’ volume to provide an adequate supply of water and nutrients that your plant needs.
  • Spray your plant roots with fungicide before repotting them in a fresh well-draining potting mix. If you opt to use the same pot, make sure you properly wash it with bleach and running water. Do not reuse the infected soil, discard it immediately.

Leaf Spot Diseases

Leaf spot diseases are caused by either fungus, bacteria, or other pathogens. Your Plumeria scientifically belongs to the shrub family. Therefore it is susceptible to having leaf spot diseases.

The spots usually start to occur on the lower branches of your plant. But it can quickly infect the leaves once the Pathogen causing the disease is blown by the wind or splashed by rain.

The shape and size of the spots vary according to the type of Pathogen. It could be angular, rounded, smooth, or with trimmed edges.

Aside from the visible black spots, your plant will also experience discoloration and wilting.

How to Treat:

  • Leaf spot diseases will not severely inflict harm on your plant, and they will tend off naturally, but still, it is always better to provide medication that will reduce the stress level of your plant.
  • If you find out that your Plumeria has leaf spot diseases, maitian 1- 2 feet of distance among houseplants. In that way, you’re allowing the air to circulate, reducing the amount of humidity in the room.
  • It is also advisable to prune your Plumeria leaves to increase sunlight penetration which is needed in Photosynthesis. 
  • Stop fertilizing your plant if it is experiencing leaf spot diseases, of course, unless you need to correct a particular nutrient deficiency.

Insect Infestation

Since your Plumeria produces sweet, healthy sap, it is not surprising that many sap-sucking insects are attracted to your plant. 

If sap-sucking insects are lurking on your Plumeria, then most likely ants are present as well.

What a pain it is if you see your plant being invaded by unwanted visitors. Is it the right time to give up your plant? Of course not. 

This might be heartbreaking, but there are still possible ways to terminate those culprits.

Check the table below to better understand what kind of insects you’re dealing with and how to control them.

Mealybugs

  • Description: Wax coated, Appeared as a cottony substance on your Plumeria leaves.
  • Symptoms: Leaf discoloration, Tip Darkening, Appearance of black spots.
  • Treatments: Rub the leaves with alcohol Use insecticidal soap If infestation cannot be controlled, dispose of the plant.

Leafhopper

  • Description: Light green in color Transparent orange-colored wings.
  • Symptoms: Leaf discoloration, Tip Darkening, Appearance of black spots.
  • Treatments: Rub the leaves with alcohol Use insecticidal soap If infestation cannot be controlled, dispose of the plant.

Spider Mite

  • Description: Microscopic in size Yellow in color Travels through the air.
  • Symptoms: Dark brown spots Leaf wilting Leaf dropping.
  • Treatments: Plant isolationSpray horticultural oil on the leaves use insecticidal soaps.

Ants

  • Description: Typical ants
  • Symptoms: Visible appearance Small holes on the tip of your Plumeria
  • Treatments: Plant isolation, Spray horticultural oil on the leaves use insecticidal soaps.

Thrips

  • Description: Brown in color Slender shape, Asymmetrical mouthparts.
  • Symptoms: Decreases growth, Leaf discoloration and Black spots on leaves
  • Treatments: Plant isolation, Spray horticultural oil or neem oil on the leaves, Also insecticidal soaps are very effective.

Excess light/scorching

Being a tropical plant, your Plumeria loves the presence of sunlight, but too much exposure might cause scorching on your plant leaves.

The common symptoms that you will see are black spots accompanied by scorched areas on the tip of the leaves.

How to Treat:

  • Transfer Plumeria to a well-shaded area where it can still receive indirect rays of sunlight.
  • Increase the watering frequency to cope up with the water shortage caused by excessive sunlight. But not too much, you don’t want to waterlog plant roots.
  • Check the draining system.

Watering Problems

Overwatering Plumeria will cause root rot disease. Plant roots will become mushy and unable to transport water and nutrients needed for the plant’s physiological needs. Because of that, there will be a shortage of Chlorophyll which is highly required in Photosynthesis.

Since your plant cannot undergo Photosynthesis, the leaves will slowly become yellowish, and soon, black spots will appear.

How to Treat:

  • Avoid watering plants during winter because they are dormant during this period.
  • Do not overwater newly planted Plumeria since it is in the rooting process. Typically, just water it once every two weeks.
  • If the plant exhibits growth by producing tips and leaves, adjust the watering frequency to once a week.
  • If you’re hesitant to water Plumeria, always check if the soil is dry.

Fertilizer Problems

Applying fertilizer is essential for Plumeria’s growth, but make sure that you’re supplying the proper nutrients the plant needs.

Check the table below so you can have a better idea of what kind of nutrients your plant requires to stop the spread of black spots.

PhosphorusProblem: Low level of soil pH causes low availability of phosphorus.
Symptoms: Visible reddish-black spots.
Corrections: Add phosphate or Phosphorus-based fertilizers.
PotassiumProblem: The abundance of Potassium causes Nitrogen deficiency.
Symptoms: Scorched and wilted leaves.
Corrections: Use eggshell to balance the soil Nutrients.
NitrogenProblem: The water solubility of Nitrogen results in nutrient deficiency.
Symptoms: Leaf discoloration and appearance of black spots.
Corrections: Add ammonium nitrate to the soil.
CopperProblem: Too much copper can burn your plant roots.
Symptoms: Leaf discoloration and growth problems.
Corrections: Add compost and chelated zinc to reduce excessive copper.

How to Prevent Black Spots on Plumeria

Aside from identifying the possible causes of black spots and applying the correct treatment that your Plumeria needs, it is also vital to distinguish the steps in preventing the possible occurrence of black spots in the future.

  1. Stop bringing home diseased plants. Make sure that you properly examine the plant before purchasing.
  1. Provide adequate watering frequency. Know the season of your plant to provide the right amount of water.
  1. Regularly check the draining system to avoid root rot and pathogen infestation.
  1. Allow 6 hours of daily sunshine. Plumeria enjoys staying under the sun, but you must be careful not to exceed 6 hours of direct sunlight, or else the plant will get scorched.
  1. Monitor the appearance of insects. In case of invasion, apply the necessary treatment stated in the table above.
  1. Supply the right amount of nutrients. Consider using a soil tester to correctly identify your Plumeria needs. The last thing you want is to spend too much buying fertilizer yet end up putting your plant at risk.
  1. Lastly, maintain a clean and organized environment. Disposed of all debris that can be used as pathogen hideouts. Always wash your hands before and after dealing with houseplants.

Final Words

If your Plumeria starts to show black spots on its leaves, immediately refer to the list of causes above to quickly attend to your plant needs. Plumeria might not demand too much of your time but bear in mind that your plant still needs sufficient attention and care.

Though it is frustrating to see that your Plumeria is having black spots, if properly treated and maintained, your plant will most likely thrive and provide the relaxing ambiance that you want.

(Sources: University of California, University of Hawaiʻi at Mānoa)

Samuel S Capra Jr

Tuesday 12th of October 2021

What type of fungicide do you recommend to use on plumerias for black and brown spots on yellowing leaves?