Also known as bar room plants, cast iron plants (Aspidistra elatior) are considered tough, low-maintenance houseplants. Although these plants can survive a lot of neglect, in my experience, they are still vulnerable to some pests and diseases. In this article, I’ll look at some of the most common cast iron plant pests and diseases and how to deal with them.
Common Cast Iron Plant Diseases and Pests:
1) Fungus Gnats
Fungus gnats are tiny black or brown flies that lay their eggs in moist soils. Once the larvae hatch, they feed on a plant’s rhizomes and roots.
I like to use sticky traps or small bottle tops filled with almond oil to eliminate adult fungus gnats. To deal with the larvae, you’ll have to replace the top few inches of soil. I like to use a mix of coco coir and coarse sand.
Mealybugs are small, white insects that thrive in warm, humid environments. These oval-shaped insects feed on plant sap, which can cause stunted growth. Mealybugs also produce a sticky substance called honeydew, which often develops into black, sooty mold.
Other symptoms of mealybug infestations include deposits of fluffy white wax and stunted growth on affected plants. Get rid of these common cast iron plant pests using insecticidal soap or horticultural oils. You can also use swabs of isopropyl alcohol to eliminate mealybugs.
3) Scale Insects
Scale insects are scaly insects that consume plant sap. Some scale insects have armored shells, while other species may be soft-shelled. Scale insects are small and rarely move, which makes it hard to spot large infestations until they start causing problems.
Symptoms of scale insect infestations include stunted growth and drooping or yellowing leaves. You may also spot deposits of sticky honeydew or sooty black mold. Eliminate scale insects using insecticidal soap or horticultural oils.
4) Spider Mites
Spider mites are tiny arachnids that feast on plant sap. Spider mites get their name from the protective layers of webbing that they use to protect their eggs. This webbing appears on the leaves and stems of infected plants.
Spider mites also cause brown or yellow mottling to develop on a plant’s leaves. Plants that are infested with spider mites may also experience stunted growth. Use horticultural oils or insecticidal soap to get rid of spider mites.
Thrips are slender, brown, or yellowish-brown insects that feed on plant sap. In my experience, they can be a common cast iron plant pests. Adult thrips also have wings, allowing them to spread to other plants. Young thrips don’t have wings and are usually paler in color than the adults.
As thrips feed, the leaves of the host plant may become dull and discolored, often displaying silvery-green patches. Thrips can also cause stunted growth and often target new, vulnerable leaves. Eliminate thrips using horticultural oils or insecticidal soap.
If you’re growing cast iron plants outside, aphids can be a common problem. Aphids are small black or green insects that feed on plant sap. These annoying pests can quickly accumulate on leaves and stems, so spotting an aphid infestation is fairly easy.
Aphids cause stunted growth and leave behind sticky deposits of honeydew, which can turn into black, sooty mold. Usually, you can dislodge aphids by spraying your plant with a hose. You can also use horticultural oils or insecticidal soap.
7) Leaf Spot Diseases
Leaf spot diseases are fungal infections that can occur on cast iron plants. These diseases are usually caused by fungi from the Fusarium genus. These fungi cause dark brown spots ringed with yellow to appear on infected leaves.
Infected leaves will not recover, so remove them at the base of your cast iron plant. If necessary, use organic copper fungicides to treat large-scale infections.
8) Powdery Mildew
Powdery mildew is a common fungal disease that thrives when daytime temperatures are warm and nighttime temperatures are cold. The main symptom of powdery mildew is the appearance of powdery white patches on cast iron plant leaves. Infected leaves may also curl or turn yellow before dropping off.
Get rid of powdery mildew by removing infected leaves and using a spray made of baking soda and water. If that doesn’t work, then you may have to use organic copper fungicides.
9) Root Rot
Root rot is a common fungal disease usually caused by overwatering. It develops quickly in waterlogged soils that have poor drainage. Root rot symptoms include brown, mushy, or smelly roots and drooping or yellowing leaves.
Only water your cast iron plant when the top few inches of soil feel almost completely dry. This helps prevent overwatering, reducing the risk of root rot.
Pesticide and Insecticide Options & Solutions
Horticultural oils are an easy and effective way to eliminate cast iron plant pests. For instance, horticultural oils like canola or neem oil (via Amazon) suffocate pests like spider mites. The oil also forms a barrier to protect your cast iron plant.
Although horticultural oils are effective, some plants are sensitive to these products. Avoid using horticultural oils on your cast iron plant during the growing season if possible.
Insecticidal soap is another easy way to kill annoying cast iron pests. The soap suffocates and desiccates pests like scale insects and thrips. However, insecticidal soap may harm your cast iron plant if you apply too much.
A homemade alternative to insecticidal soap is a mix of dish soap and warm water. However, dedicated products like this one often work better.
Sticky traps are an excellent way to eliminate adult fungus gnats and other pests. While sticky traps won’t kill fungus gnat larvae, eliminating the adults prevents them from laying more eggs. Sticky traps are relatively easy to acquire and use.
Fungicides are used to treat fungal infections and diseases that have infected your cast iron plant. Organic copper fungicides are preferable to synthetic fungicides as the latter can kill beneficial soil organisms.
Apply fungicides sparingly and always follow the instructions on the packet. This organic copper spray from Bonide is an excellent choice.
Managing Cast Iron Plant Pests and Diseases
While insecticidal soap and horticultural oils eliminate pests quickly, prevention is almost always the best cure to mitiage against common cast iron plant pests and diseases. Providing great care is the best way to protect your cast iron plant from diseases and pests.
Cast iron plants grow best in bright, indirect light but also thrive in low-light conditions. Ensure your plant gets at least 3 hours of bright morning sunlight daily. Cast iron plants also need loose, well-draining soils that can still hold some nutrients.
Water cast iron plants once every week or two. Always check that the top few inches of soil feel dry to the touch before watering. This helps prevent overwatering, which can lead to root rot.
Cast iron plants can be grown outdoors in USDA Zones 7 to 11. To keep pests and diseases at bay, give your cast iron plant plenty of space away from other plants. This promotes good air circulation and prevents diseases and pests from spreading to your cast iron plant.
For more, see our in-depth guide on where to position cast iron plants for optimal care and feng shui benefits.
Common Cast Iron Plant Pests and Diseases – Wrapping Up
Cast iron plants are low-maintenance houseplants that can tolerate some neglect. However, cast iron plants are still susceptible to diseases and pests like fungus gnats, spider mites, and root rot. Treat fungal diseases using fungicides and eliminate pests using horticultural oils or insecticidal soap.
For more, see our in-depth guide to whether cast iron plants are toxic to pets and humans, when and how to fertilize cast iron plants, and the amazing uses and benefits of cast iron plants.
If you’re looking for your next cast iron plant to add to your collection, see our guide to the best live plant delivery services.
Edd is a budding content writer and gardener living in the United Kingdom. He has a bachelor's degree in Creative and Professional Writing and has written for several gardening publications online. He is passionate about nature and sustainability with a focus on gardening and wildlife.