Rhamnus (Buckthorn) is the alternative host of Oat Crown Rust; this disease alternates between buckthorn and cereal crops and grasses. While buckthorn is the primary woody host, the disease is also present on other species. If there are oat fields within 1/2 mile of your buckthorns, it is unlikely you will be able to eradicate this problem.

There is no control for the disease; however, you can try applying a copper-based fungicide as soon as the leaves emerge (too late this year). Be sure to select a fungal spray that lists crown rust as susceptible. Fungicides are preventative and should be applied as soon as orange spots appear on the leaves. These sprays will not kill or remove existing rust but may help prevent the spread.

Another control method would be to remove leaves and stems that have rust on them and dispose of them. Do not compost or leave them lying around on your property. Be sure to rake up and destroy the leaves that fall in autumn as the spores can overwinter lying on the ground under your buckthorns.

As with any other fungal disease, the spores are spread easily by wind and rain onto other grass and cereal plants. It is host-specific and will not affect your other trees, shrubs or ornamental plants.

Buckthorn is considered a weed by most people. Even the hybrid "Fine Line" (Rhamnus frangula) is restricted and cannot be shipped to these states: CT, IL, MA, ME, MN, MT, NH, NY, VT, WI. You may wish to consider removing these plants and replacing them with another plant.

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My pleasure. Good luck!