Rust is a collective term for a type of plant disease caused by fungi and characterised by the appearance of rust-coloured mould growth over different parts of the plant's anatomy. One such disease is garlic rust, a disease that has caused significant damage to agricultural garlic crops and can also cause problems for home garlic growers. Garlic rust can be effectively managed, however, by natural methods that eliminate the need to use potentially toxic fungicides.
Garlic rust is caused by the fungus Puccinia allii (also sometimes called Puccinia porri). If your garlic plant is infected, you will notice small spots coloured white or yellow on the garlic plant's leaves. As the infection progresses, entire leaves can appear orange, and raised pustules called uredinia break out on the leaves. The pustules contain urediniospores and teliospores that spread the fungus to neighbouring plants and eventually turn black.
Preventive Control Methods
Preventive methods for controlling fungal diseases in plants usually involve planting disease-resistant cultivars of the plant; this may not be an option in the case of garlic rust. Ongoing research into disease-resistant garlic cultivars has shown some promise, but for the most part, no cultivars that are entirely resistant to the disease have been discovered. Even those cultivars that showed a marginal resistance to the disease are not commercially available.
Natural Control Methods
Since preventive measures are not a viable option in the case of garlic rust, it is necessary to consider natural methods to treat a garlic plant that has already been infected. Crop rotation has shown a high degree of effectiveness in this capacity, since the spores of the fungal disease agent are spread via wind and rain to neighbouring plants. For minor infections, cut away diseased parts of the garlic plant and destroy them at once. Severe infections may mandate that the garlic plants be removed completely and replanted in a different part of the garden.
Even though natural methods are always preferable over methods that employ the use of fungicidal chemicals, garlic rust management is nearly impossible without the use of an approved fungicide. Purchase a fungicide approved for control of garlic rust and apply according to the manufacturer's directions. Preventive or systemic fungicides are typically more effective at controlling the disease than are fungicides applied to plants that are already infected.
- University of Arizona Extension Plant Pathology: Onion Garlic Rust
- University of California Agriculture and Natural Resources; Rust Disease Continues to Threaten California Garlic Crop; Steven T. Koike, et al.
- University of California Agriculture and Natural Resources Statewide IPM Program: Onion and Garlic Rust