Common Plant Diseases: Causes, Symptoms, and Prevention

Healthy plants are the norm; diseases strike when conditions favor pathogens. Understanding bacteria, fungi, and viruses helps you fight back.

Disease Science 101

Water at the base to keep foliage dry. Bacteria (single-celled) live inside plants, spread by insects, water, hands. Fungi live on plants, cause visible symptoms, spread by water, wind, insects. Viruses are smallest, hardest to control; spread by insects, seeds, tools. Disease needs a susceptible host (stressed plant) and ideal conditions (humidity, dryness, cloud cover).

Common Symptoms

Leaf spots (most common), sudden wilting, ragged/curling leaves, deformed flowers/fruit, mottled foliage, poor growth.

Notorious Diseases

Bacterial spot: Damp, humid weather. Dark brown lesions with yellow halos. Avoid working among wet plants.

Black spot: Common on roses. Dark leaf splotches, leaf drop. Wet weather accelerates. Improve air circulation; water at base.

Mosaic virus: Incurable. Yellow/green mottling, distorted leaves. Destroy infected plants (peonies, etc.) to prevent spread.

Powdery mildew: White powder on foliage in dry, humid conditions. Space plants for airflow.

Rose rosette: Viral, spread by tiny mite. No cure. Remove infected plants. Symptoms: thick reddish stems with excessive thorns, witch's broom growth.

Rust: Orange/gold/brown-red spots from several fungi. Mostly cosmetic. Healthy plants overcome it.

Prevention Is Key

• Space plants for air circulation.
• Grow in proper sun, water correctly, avoid over/under-fertilizing.
• Spray susceptible plants with homemade fungicide: 1 tsp baking soda + 1 tsp horticultural oil per quart water.
• Remove and trash affected plant parts.