Hoyas are relatively non-toxic plants that produce fragrant flower clusters and beautiful vines filled with thick waxy leaves. However, even with their simplicity and beauty, Hoyas are still vulnerable to brown spots.
The appearance of brown spots can be attributed to diseases such as bacterial leaf spots, fungal leaf spots, and algal leaf spots. Inadequate environmental conditions such as temperature extremities may also lead to the same results. At some point, pests can also be the culprit for brown spots on your Hoya.
In this article, we will discuss what causes the brown spots and how to treat and prevent them.
What Causes the Brown Spots on Your Hoyas?
Brown spots on plants are a sign of an impending or an occurring disease. The following will show you what causes the brown spots and other symptoms your Hoyas might get.
Symptoms may be the same for most cases, so observe thoroughly, and apply the right and proper treatment.
Water is an essential ingredient for plants to thrive and survive. However, improper watering techniques may lead to unwanted results, including death.
Overwatering is one of the most common problems you may probably encounter.
It is a case in which the abundance of water in plants causes the root system to drown and slowly die (root rotting). Thus resulting in water stress, turning their leaves completely yellow or brown.
Having a plant saucer, on the other hand, may also cause overwatering. It causes the drained water to move back up, soaking the roots for a prolonged time, resulting in root rotting.
Underwatering, contrary to overwatering, results in plants having dry and wrinkled leaves and stunted growth.
Hoyas may produce brown spots and freckles due to a lack of water in their system. Brown spots in Hoyas may appear to be dry and have a lifeless texture.
Moreover, you may see some symptoms along the way, such as the leaves turning yellow.
Hard Water Spots (White Spots)
Hard water contains lime, salts, and mineral deposits. As the water on the leaf surface evaporates, sediments are being left out as a white spot. Usually, calcium and magnesium are the most common sediments found in hard water.
However, aluminum, iron, and manganese may also be found in some areas. You may be confused but hard water is simply just your normal tap water.
Edema, also written as Oedema, is a plant physiological disorder that develops when there is a faster rate of water absorption from the roots, leaving other parts of the plant dehydrated.
Water pressure builds up in the leaves’ internal cells which causes blisters. They are commonly found on the undersides of the leaves.
This disorder is most prevalent at the end of winter and when there is a long period of cloudy weather.
Blisters on edema eventually erupt forming white or brown wart-like spot growths. Leaves may completely turn yellow and fall off as the condition progresses.
Fungal Leaf Spot
Fungi are the most common disease-causing agent for plants. They cause severe damage that eventually results in death. Check your plants regularly to prevent this from happening and from spreading.
Botrytis Fungal Infection
Botrytis blight is a common disease found in plants caused by Botrytis cinerea. As the infection progresses, the leaves become mushy and spongy to touch.
Plants would eventually rot as the leaves begin to fall. Common symptoms include stem lesions that may be black or brown, wilting, and dry or mushy roots.
Rotting of roots may be unnoticed until the disease has severely progressed. This is because of Hoya’s waxy leaves that inhibit wilting.
This infection is caused by the fungi belonging to Colletotrichum species.
Colletotrichum orbiculare causes brown spots with yellow outlines on Hoya leaves. Other species include Colletotrichum richelle.
Infected leaves have large brown spots with a gray tint and gray spores. They usually affect the plants living in rainy, humid and warm climates.
Also, spores produced by these fungi may spread to other plants due to rain, insects, wind and gardening tools.
Wounded plants are most likely to get infected since they are more open to contamination than their unwounded counterpart.
If you’ve used an infected tool, the transfer of the disease-causing agent is most likely to occur.
Septoria Leaf Spot
This fungal disease is caused by Septoria lycopersici which are commonly found on tomatoes. However, your Hoyas might get infected by them too.
Symptoms may appear as spots with brown margin and gray or tan-colored centers. Yellow halos may also appear circling around the spots.
As the disease progresses, spots may merge forming a larger one, and in severe cases, leaves will dry out and fall off completely. Leaves turning yellow is a sign that the disease is already severe, so watch out.
Alternaria Leaf Spot
Commonly caused by Alternaria species, this fungal disease is a common problem for many fruits and vegetables. However, it may also affect indoor plants like your Hoyas.
Usually, you’ll see dark brown, yellow or black spot on its early stages. On severe cases, your plants may have damaged stems in the form of lesions. After that, the entire plant will eventually wither, fall off, and die.
This is a common problem for locations with high humidity. It is caused by a wide range of fungi and affects almost all types of plants.
You will start to see it as a white or gray powder coating the plant’s leaves and fruits. If you left this untreated, Hoya leaves may turn yellow or brown.
This is caused by Pseudoperonospora cubensis, an oomycete and not a true fungus. It can start infecting plants at a wide range of temperatures from 41-86°F (4-28°C).
Under humid conditions, mildew spores rapidly reproduce and spread, severely damaging the plant. However, it only grows on living plant tissue and a moist leaf surface.
Make sure to look out for pale green to yellow spots that usually form at the upper surface of Hoya leaves, which later turns brown.
Algal Leaf Spot
Commonly known as the green scurf, algal leaf spot is mainly caused by Cephaleuros virescens. Algal leaf spot targets plants living in warm and humid climates, making Hoya plant species susceptible to this problem.
Branches and twigs can also be affected resulting in reddish-brown or pale green lesions.
Spots are marked by gray, green, orange, or brown on the leaves. The only good thing about this is that it rarely causes death to plants.
Most plants suffering from this disease survive, so you don’t have to worry about the death of your plant.
Bacterial Leaf Spot
This disease is caused by the bacteria Erwinia carotovora. During the early stages, you’ll see the presence of yellow or light brown spots on your Hoya leaves. This usually happens in a warm and humid environment.
Such environmental conditions promote the growth of the responsible bacteria. You’ll most likely see water-filled blisters on the undersides of their leaves as the disease worsens.
Leaf Burn/Excess Light
Hoyas don’t need excessive sunlight, otherwise, it may lead to mild sunburn producing brown to red spots.
Also, too much sunlight can slowly kill your plant by creating potentially deadly free radicals and altering your plant’s water cycle. This dries them out to the point where it has no longer water to use for photosynthesis and growth.
Check your plants regularly, especially during summer seasons where the rate of moisture evaporation is high. Leaf burn may start as a brown spot on the tip of your plant’s leaves.
Hoyas are tropical plants that need a temperate weather climate to survive. Placing them in a cold and freezing location will decrease their rate of survival.
Brown spots may be expected as a sign of damage done by cold extremities, which is usually seen after the leaves have been thawed out.
Keep in mind that frost damage is irreversible. All you can do to save your plant is to remove dead leaves, feed, and hydrate them properly.
Chemical burns from too much fertilizer may take place if you feed your Hoyas excessively. Fertilizer contains salts and too much salt can draw the moisture out of plants leaving them dry.
Like every other being, Hoyas want to receive the right amount of food to acquire nutrients, which are necessary and functional for living.
Brown spots on the tip of the leaves may appear if you excessively feeding your plants with fertilizer.
Like you, plants also need nutrients to survive. They need a proper intake of macronutrients (mobile) such as nitrogen (N), phosphorus (P), magnesium (Mg), molybdenum (Mo) and potassium (K), and micronutrients (immobile) such as iron (Fe), zinc (Zn), manganese (Mn) and copper (Cu).
If your plant has a mobile nutrient deficiency, older leaves will suffer first. These nutrients can move to the priority leaves which are the younger ones. On the contrary, younger leaves will suffer first if the plant lacks immobile nutrients.
In most cases, deficiency starts with chlorosis, in which the plant tissue turns yellow, and ends with necrosis, in which the plant tissue turns brown and dies.
Hoya plants attract a lot of sap-suckers such as mealy bugs, aphids, scale insects, and spider mites.
If you happen to see these insects, eliminate them right away before they damage your plant. They usually leave brown lesions after they suck out the plant nutrients.
These insects start at small numbers so remove them before they multiply. It will not be easy to deal with a swarm of different insect pests on your plants.
How to Treat or Prevent Brown Spots?
Great question! After finding out several causes, now we need to know how to address these issues.
Solving Watering Problems and Preventing Edema
Watering problems is one of the most common problems that we encounter. Such a common problem requires a very easy solution.
- Water them only when they need it. Check the soil moisture of your plant to determine when to water.
- If your Hoya is placed indoor, reduce the amount of water as it evaporates slowly due to lesser sunlight exposure. Add if otherwise.
- If root rot has already taken place, remove the rotten roots and transfer the plant to a new pot.
- If the plant looks wither and dry, water them immediately and observe the following weeks.
- For hard water spots, wet a clean paper towel with lemon juice or a solution containing 2 cups of water and a teaspoon of vinegar. Wipe the upper leaves in a circular motion avoiding the undersides and the stomata.
Treating Fungal Leaf Spot
For Botrytis Infection
- If your Hoya is inside your home, isolate them from other plants to improve air circulation
- Use mulch or organic compost. These will prevent fungal spores from going back up onto leaves.
- If you found any diseased leaves, destroy and remove them immediately.
- Apply fungicides. You may apply it in advance as protection for your plants.
- Isolate the diseased plants. This prevents the spread of the disease to your other plants. Also, disinfect your tools to avoid cross-contamination.
- Clean and remove the diseased leaves immediately to prevent the spread of the disease.
- Ensure proper lighting conditions, adequate water, and enough fertilizer to strengthen your plant’s immunity.
- You may use fungicides such as copper sprays or sulfur powders but only apply them if your plants are in a severe condition.
- If you have suspected soils, don’t take any chances, remove them and use a clean one. Septoria may overwinter in soils waiting for new plants to infect.
- Remove and destroy the diseased leaves and plant debris immediately. This is to prevent the disease from spreading and infecting your other plants. Also, make sure to wash your hands properly.
- Place your Hoyas on a cool and shady place. Warm temperatures are favorable conditions to the fungi responsible for this disease.
- Please avoid overwatering your plants. This helps the fungi to spread entirely.
- Ensure proper spacing and isolation to improve air circulation and prevent other plants from having the disease.
- Apply fungicides. You may use copper-based or potassium bicarbonate. It is best to spray fungicides on the early stages of the disease.
- Remove and destroy the diseased leaves immediately to prevent the disease from spreading.
- Alternaria can overwinter in soil. Make sure to choose a resistant variety of Hoya.
- Prune plants to improve air circulation. Make sure to sanitize and disinfect your pruning tools after making cuts.
- Ensure proper spacing between your plants. This improves the air circulation around them and prevents other plants from being infected too.
- Apply fungicides. You can use copper-based or sulfur-based fungicides. These are effective in treating and preventing fungal diseases.
For Powdery Mildew
- After you have cleaned up the soil, cover it using a thick layer of mulch or organic compost. These will prevent fungal spores from splashing back up onto the leaves.
- Occasionally wash the leaves to disrupt the daily spore-releasing cycle.
- Spray plants with a peroxide solution. The solution can be made by mixing 9 parts of water and 1 part of hydrogen peroxide.
Treating Downy Mildew
- If you found some infected leaves, immediately remove and destroy them to prevent the disease from spreading.
- Apply fungicides at the early stage of infection to prevent and control them from spreading. Always use organic fungicides.
Treating Algal Leaf Spot
- Avoid overwatering. Prolonged wetness encourages the growth of algae on the surface of the leaves.
- Trim and remove any diseased leaves immediately to prevent them from spreading to your other plants.
- You may use fungicides such as copper sprays or Bordeaux mixture but only apply them if your plants are in a severe condition.
Preventing Bacterial Leaf Spot
Sadly, there is no treatment for Bacterial Leaf Spot. However, there are preventive measures to stop it from happening again.
- Spray your plants with baking soda solution. Solution can be made by mixing a tablespoon of baking soda, 2 ½ tablespoons of vegetable oil, a teaspoon of liquid soap, and a gallon of water. Spray only a small amount and check for possible reactions before applying it again.
- Use copper-based fungicides to protect and coat their leaves preventing
- Water your plants early in the day and give them adequate air circulation. It is best to grow your Hoyas at a temperature not exceeding 70°F (21°C).
- Remove and destroy any diseased leaves immediately.
Treating Frost Damage, Chemical and Leaf Burn
- Check your fertilizer if it contains high doses of fertilizer salts. You may want to substitute it with a lower dose. Salts are usually removed when you are watering your plants so don’t worry too much.
- If your plant is placed beside the window, make sure to open it or close the curtain. Window glass can magnify and radiate heat faster so watch out, they might get sunburned before you know it.
- If your Hoya suffers from leaf burn during winter season, try to raise the temperature and humidity of the surroundings.
Treating Nutrient Deficiency
- Observe symptoms present and determine what nutrients are causing the problem. Check the area of the symptomatic leaves. Older leaves indicate mobile nutrient deficiency, and younger leaves indicate immobile nutrient deficiency.
- To treat nitrogen deficiency, it would be best to use nitrate or ammonium-based fertilizers. You may also use organic fertilizers which are low in salts.
- To treat phosphorus deficiency, transfer your plant to a cool and shady place. Plants absorb less phosphorus at higher temperature conditions.
- To treat potassium deficiency, use fertilizers low in sodium, calcium, and nitrogen, especially when the plant is in the flowering stage where there is a great need for potassium.
- To treat magnesium, zinc, and calcium deficiency, always maintain your nutrient solution at a pH level of 6. At this level, your plants absorb these nutrients easily.
Treating Brown Spots Caused by Pests
- If you found some aphids, thrips, or spider mites, apply insecticidal soaps. You may coat it to your plants or spray it to them continuously.
- If you found some fungus gnats and whiteflies, sticky traps may be used. You can also dry the soil to completely kill any pre-existing eggs.
- If you found some mealybugs, remove the diseased branches and rub them with alcohol.
- If you found some scales, remove them using a soft brush.
- Remove and destroy infested leaves and stems to prevent them from infesting other parts.
- Use pressurized water sprays. Pests can’t keep up with the continuous pressure coming from the water. They’d have no choice but let go of the plant.
- Apply organic pesticides, horticultural oils, and insecticidal soaps. This helps greatly in removing those pests infesting you plants.
What are the Best Tips to Prevent Brown Spots on Your Hoya?
- Start with a healthy, resistant, and vigorous Hoya. Choose to buy the best quality Hoya plant whenever possible.
- Always clean the tools and pots you’re going to use before planting.
- Ensure sterilized and proper potting mix. Make sure that you use the right one for your plant. Sterilization kills all the possible microorganisms saving your future plants.
- Pot size should be appropriate to the size of the plant to ensure proper growth.
- Prune plants when needed to develop good air circulation and decrease the possibilities of proliferating microorganisms.
- Apply an adequate amount of fertilizer. Fertilizers come in different variants, always choose the best and appropriate one for your plant.
- Give them an adequate amount of water, not too little and not too much. Make sure the top 2 inches of the soil are dry before you water them.
- The best time to water your plant is early in the morning. This prevents the growth of microorganisms that may cause you great problems.
- Find the best spot for your plant. It should have proper lighting conditions and has high humidity.
- Monitor your plant’s growth occasionally. If you see some disease or infected leaves, don’t be afraid to take and remove them. This will stop the disease or infection from spreading.
Hoyas are great houseplants, not only they are beautiful and vibrant, but they are also easy to grow and manage. Just make sure that you give them what they need and it will never cease to amaze you. Happy planting!