Fungicides

Fungicides are chemicals or organisms that kill or inhibit fungi and fungal spores. Since fungal diseases are responsible for significant agricultural losses, understanding the use and limitations of fungicides can protect your plants.

Peach leaf curl (Kate Russell)

How do fungicides work?

Fungicides work in one of three ways:

• Direct contact fungicides only work where they touch the plant.
• Translaminar fungicide applications are absorbed through upper leaf surfaces and moved to lower leaf surfaces.
• Systemic fungicides are absorbed into the vascular bundle and moved throughout the plant in the xylem.

Fungicide ingredients

Sulfur, neem, rosemary, and jojoba oils are ingredients of most fungicides. Sometimes you can add beneficial bacteria (Bacillus sabtilis) and fungi (Ulocladium oudemansii) to fungicides to improve their effectiveness. Fixed copper and Bordeaux mixtures also work as fungicides. Over-the-counter fungicides commonly contain cadmium,  copper, mercury, and tin, which can reach toxic levels in your soil.


​Fungal diseases treated with fungicides

Fungal plant diseases include anthracnose, blights, cankers, damping off, downy mildew, galls, powdery mildew, rusts, scabs, spots, and Fusarium and Verticillium wilts, among others. Unlike most fungal diseases, fungicides do not work against Fusarium and Verticillium wilts.

Rust on rose leaves (Kate Russell)

While fungicides can be effective, prevention is a better course of action. To reduce the chance of fungal diseases, install resistant resistant varieties, improve airflow with good pruning, avoid overhead watering, and remove diseased plant tissue. Ensuring good drainage is another way to reduce the need for fungicides.