If you notice black spots on hoya leaves it can be super stressful, so I’ve created this guide to go through all the reasons and when you should be worried (and when you shouldn’t!).
Black spots on hoya leaves are usually caused by leaf spot, pests or issues relating to overwatering. Leaves that become affected by black spots will need to be removed and the root of the problem dealt with to get your hoya back to health.
Let’s get straight into it.
6 Reasons For Black Spots On Hoya Leaves
Let’s take a look at the 6 most common reasons and what you can do about it.
1. Sooty Mold
Sooty mold is a type of mold that grows in honeydew and secretion from common plant pests. These include common houseplant pests such as scale or aphids.
Sooty mold is quite easy to spot as it looks very similar to ash or soot as the name implies. The image below shows an example of sooty mold on a generic plant leaf – I would have included an image of one of my hoyas but I have luckily yet to face this problem.
Sooty mold reduces photosynthesis and can spread quickly to other leaves so it must be dealt with quickly.
How To Deal With Sooty Mold On Hoya Leaves
Sooty mold is difficult to remove once it has grown, but the first step to dealing with it is to remove the pests that are causing it in the first place.
There are multiple pests that can cause sooty mold, so I highly recommend this guide by Mississippi State University which provides all of the relevant control methods for these pests.
Once you have dealt with the pests you can either trim the leaves that have been affected or you can spray the leaves with a mixture of detergent and water. To do this mix 1 tablespoon of liquid detergent per gallon of water and spray it onto the leaves, leave it for 10 to 15 minutes and then rinse the leaves with a strong stream of water.
Sooty mold isnt the only way pests can cause black holes on hoya leaves.
Some pests, such as aphids, can gather in large amounts and discolor leaves when they feed from the sap in the leaves. Scale insects (there are 8,000 different species of these) can also discolor hoya leaves as they feed on the sap.
You may also mistake certain pests for black spots, particularly spider mites which are very hard to see with the naked eye but often group together to make what look like black spots.
Serious pest infestations can actually kill hoyas pretty quickly, so it’s crucial to deal with them as soon as you notice them.
How To Get Rid Of Pests On Hoyas
Hoyas can be affected by a lot of different pests, so again I would recommend this guide to learn about each one and their control.
Overwatering is a very common issue for hoyas (and just about every other houseplant as well).
If your hoya is overwatered for an extended period of time then it is likely that root rot will develop and turn the roots mushy and brown/black. The leaves will quickly follow and turn yellow initially and then brown and black.
How To Care For An Overwatered Hoya
The first step I recommend is to check the soil and roots, as there is a good chance the roots will have been affected by root rot. If the water is saturated and the roots have started to rot then remove the plant from the soil and rinse the roots with water.
Trim any rotten roots with a sterilised pair of trimmers and treat the rest with a fungicide solution. Clean the pot with bleach and then repot the plant in fresh soil and water moderately, allowing any excess to drain out of the holes.
Sometimes leaves on a hoya will die simply due to age. This is completely normal and usually affects the leaves closest to the roots at first.
Leaves that are dying will change color and can develop black, yellow or brown spots and patches.
The best thing to do here is to let the leaves die off fully and then trim them away. You can trim them away as soon as they start to die – I know a lot of people don’t like how dying leaves look – but there is research to suggest that plants reabsorb nutrients from dying leaves so take from that what you will.
5. Leaf Spot
Leaf spot is a broad term used to describe spots on plant leaves caused by several types of fungi.
The development of leaf spot is favored by damp conditions, so standing water on the leaves (i.e water droplets) should be avoided.
How To Deal With Leaf Spot On Hoyas
There are a few things you can do to both prevent and deal with leaf spot on hoyas:
- Remove affected leaves as soon as possible to prevent the spread of fungus.
- Ensure humidity isn’t too high. Most hoyas prefer higher humidity, but it shouldn’t be left too high as reduces the amount of water that can evaporate off the leaves.
- Avoid misting – Misting is not an efficient way to improve humidity as it only has a short-term impact, but it can also lead to leaf spot if the water droplets are not evaporating quickly enough from the leaves.
- Improve circulation over the plant – Again another measure to improve the evaporation of water from the surface of the leaves.
It’s worth noting that fungicides can be used but you should only opt for that if the above steps haven’t worked. In most household situations these steps should work well, and it can be tricky to choose the right type of fungicide as leaf spot can be caused by many different fungi.
6. Sun Scorch
Although hoyas need plenty of sunlight to grow, most prefer bright indirect sunlight
If your hoya receives too much direct and intense sunlight each day it can actually scorch the leaves. Sun scorch (also known as sunscald and sunburn) can cause yellow spots on the leaves that eventually turn black or brown and die.
How To Deal With A Sun-Scorched Hoya
If your hoya has been scorched by the sun it is likely to only affect a few leaves at a time rather than all of the leaves on the plant, as the lower leaves benefit from the shade as well as those that are out of direct sunlight.
Leaves that are scorched need to be removed as they will not recover. Aside from that, all you can do is move your hoya to a different location with less direct sunlight and make sure it is watered properly.