How to Spot and Treat Fungal Diseases

Fungal diseases are common in plants. Some, like blight, are confined to outdoor plants, especially tomatoes. Others hit houseplants of all kinds. The causes are varied. Overwatering is the biggest culprit but too cool temps or too much humidity are also factors. Here is a look at the most common fungal diseases and how to treat them.

Crown Rot: This affects plants like African Violet that grow outward from a single stem. It’s usually caused by overwatering or by allowing water to stand in the center of the plant. Symptoms include brown or yellowed leaves, blackened or mushy stems and a general plant collapse. Once Crown Rot has begun it is impossible to stop. The only treatment is to take cuttings from any remaining healthy stems and discard the plant. To prevent use a moisture meter to prevent overwatering and never pour water into the center of a plant.

Leaf spot: This affects a wide variety of plants. Symptoms include sunken, soft brown spots on leaves, a black or brown dust on leaves and leaf drop. It’s caused by poor ventilation and high humidity. To treat, remove affected leaves, increase ventilation and spray plant with a homemade or commercial fungicide. A dehumidifier may also prove helpful.

Powdery Mildew: This affects a wide variety of houseplants, but tuberous begonias are particularly prone to this disease. Symptoms include a white or gray coating on leaves, deformed new growth, and wilting or curling leaves. It’s caused by poor air circulation or by weather that involves warm, humid days and cool nights. To treat, increase ventilation and remove affected leaves. Spray with a homemade or commercial fungicide.

Mold: Sometimes a white mold will form on the soil surface. If not caught in time it can spread to the plant itself and cause stem rot. The mold is usually the result of overwatering combined with cool conditions. If caught early, scraping the mold off the soil with a spoon and reducing watering is an effective treatment. If the mold returns, repotting in fresh soil is the next step. If it has spread to the plant itself little can be done.

To make an effective homemade fungicide, try a solution of one gallon of water mixed with a tablespoon of baking soda and 3 tablespoons Neem oil or dishwashing liquid. Pour into a spray bottle and spray plants liberally. Some houseplant books recommend spraying plants with ordinary household Lysol but that is not recommended as it can damage leaves.