Cool, rainy spring weather has likely encouraged the disease to develop. By May, the disease continued to spread and satisfactory control was not achieved with the few registered fungicides available for garlic, though in most cases these materials were applied after disease was already well established. Rust is not a new disease for California, and it was observed in our state at least as early as 1934. Worldwide, the fungus causing rust on garlic has been observed on plants in the Allium or onion family generally wherever these crops are grown. Symptoms Garlic rust is readily identified.
Early symptoms consist of small yellow to white flecks, streaks, and spots on leaves.
Severely infected leaves can be almost entirely covered with pustules, resulting in complete yellowing, wilting, and drying of the leaf. Severe rust on garlic and other Alliums can cause extensive loss of foliage and subsequent reduction in bulb size and quality. The orange pustules often form concentric groups on the spot periphery. This fungus can infect chives, garlic, Japanese bunching onion, leek, onion, rakkyo, and shallot. The pathogen may exist in the form of different strains or races in that a particular isolate will infect certain plants in the onion family while at the same time not be able to cause disease on others.