Crown rust, caused by the fungus Puccinia coronata, needs to infect both buckthorn and an alternate host to complete its lifecycle. The alternate hosts in Minnesota are cereals and grasses, including oats, ryegrass, and bluegrass. The fungus survives winter in the alternate host (oats) and produces spores in the spring. These spores are wind blown to buckthorn, where new infections begin.

Crown rust initially appears on the upper leaf surface, petioles, and stems of buckthorn as swollen, yellow-green spots. Clusters of white, tube-like cylinders (called aecia) are produced from spring to early summer on the lower leaf surface, petioles, and stems. These structures contain masses of orange-yellow, powdery spores that are wind blown to the alternate host. Orange to rust colored lesions (filled with urediospores) on the leaves of the alternate host cause repeat infections throughout the summer. When severe, crown rust can cause huge economic losses of alternate hosts such as oats. In late summer, reproductive structures called telia develop on the leaves, then lie dormant until the following spring.

Crown rust does not harm buckthorn, therefore no chemical control is recommended. Since crown rust infects a number of alternate hosts, removal of the alternate host is not a practical alternative. In addition, certain species of buckthorn are considered invasive plants. Therefore, common buckthorn is no longer recommended for planting.

References

Sinclair, W.A. et al. 1987. Diseases of Trees and Shrubs. New York: Cornell University Press.

Everett, Thomas H. 1981. Encyclopedia of Horticulture: The New York Botanical Garden Illustrated Vol. 9. New York and London: Garlan Publishing Inc.

P418B
Revised 2/2000
Chad Behrendt, Crystal Floyd