Plant Parent Basics: Disease
A perfectly disease free Monstera delicious leaf. Note the rich green color and unblemished leaves.
As part of our feature series, Plant Parent Basics, in this article you will learn about common house plant diseases and how to avoid them.
What is plant disease?
Just like people, plants can get sick and diseased. The appearance of disease is usually a sign of poor growing conditions.
Most plant diseases are caused by fungi, bacteria and/or viruses. The Phalaenopsis orchid shown here is presenting symptoms of a viral infection. Photo courtesy of Missouri Botanical Garden.
What kind of plant disease are there?
There are many different kinds of plant diseases. The following list details how to identify, treat and prevent the most common houseplant diseases.
Grey mold
This disease presents as grey, fluffy mold which can cover all parts of the plant. It commonly occurs in environments that are cool, humid and still. To eradicate grey mold, cut away and destroy all affected parts. Remove any moldy soil, spray the plant with a systemic fungicide, and reduce watering and misting, as well as improve ventilation.
Root rot
The first sign of this disease is usually yellowing and wilting of the leaves which is quickly followed by browning and collapse. The cause is fungal decay of the roots due to water logging. You can only save a plant from root rot if the disease is spotted and treated in time.
To treat root rot, you need to replant the affected plant in fresh soil with good drainage to avoid standing water. It is also recommended to gently wash diseased roots and remove all brown, soft parts of the roots with a sterilized pair of plant shears.
Sooty mold on a Ficus elastica leaf. Image courtesy of Reddit.
Sooty mold
A black fungus which grows on the sticky substance deposited by plant pests such as scale, whitefly and mealybugs. The unsightly mold does not directly harm the plant, but it does reduce growth by blocking the plant’s pores and shading the surface from sunlight. Remove sooty mold by wiping plant with a damp cloth. Control future attacks by spraying plant with neem oil.
Crown, stem and basal rot
This disease presents as part of the stem or crown has turned soft and rotten. When the diseased area is at the base of the plant, it is known as basal rot. The fungus usually spreads rapidly and kills the plant. If you have caught the disease early you can try to save it by cutting away all diseased tissue. If not, you will need to throw the post, soil and plant away. To prevent crown, stem and basal rot avoid overwatering, under watering, and keeping the plant too cool.
Leaf spot
Leaf spot presents as brown, moist spots that appear on the leaf of the plant. In a bad attack the small spots enlarge and merge, killing the whole leaf. Both bacteria and fungi cause this effect. The best general is to remove and burn infected leaves, spray the plant with systemic fungicide and keep it dry without misting for several weeks.
Powdery mildew a shown on an African violet. Photo courtesy of Purdue Agriculture.
Powdery mildew
This is a fungus disease which grows on the surface of leaves, spotting or coating them with a white powdery deposit. Unlike grey mold, this disease is not fatal, but it is disfiguring and spreads quickly. To treat powdery mildew, removed mildew leaves and spray the plants with a systemic fungicide and improve circulation are the diseased plant.
Virus
There is no single symptom of virus infection in plants. The growth may be severely stunted and stems are often distorted. The usual effect on leaves the appearance of pale green or yellow spots or small patches. The infection is almost always brought in by an insect or was already present in the plant at the time of purchase. There is no cure, the only way to deal with virus is to throw the plant away if you are sure of the virus diagnosis.
Basal rot on a barrel cactus. Image courtesy of Arizona Daily Star.
What do I do if I suspect my plant has a disease?
Act quickly. Cut out the affected area as soon as you notice it, use a fungicide if recommended (see above) and correct the cultural fault, such as repotting or root rot surgery.
If you’re unsure how to diagnose your plant, please reach out to us via email or a direct message via Instagram. Pictures are encouraged.