Issue 3, May 19, 2021

Crown Rust of Common Buckthorn

May is Illinois Invasive Species Awareness Month. Common buckthorn (Rhamnus cathartica) was one of the first invasive species that I was introduced to. Readers in the northern portion of the state are likely to be familiar with this pest, as it has invaded and overtaken woodland areas by easily out-competing native plants for light and moisture. I learned firsthand how invasive and destructive this plant was during a high school class that used a Kane County Forest Preserve as a "classroom." Since then, I've spent countless hours clearing common buckthorn to reclaim woodland habitat. Buckthorn puts up a fight with every step from cutting to dragging and trying to load it into a brush chipper.

Unfortunately, common buckthorn is a tough and adaptable tree with few pests. You will occasionally find crown rust (Puccinia coronate) infecting its leaves. However, the disease doesn't cause enough injury to assist with eradication efforts.

Photo 1 Crown Rust on upper leaf surface of common buckthorn

Crown rust causes yellow to orange spots on buckthorn leaves, petioles, and green stems. They are hard to notice from a distance, and they don't seem to affect the trees' health significantly. However, these infections are an important source of inoculum for crown rust of oat in the north-central states. Moderate to severe epidemics on cultivated oats can reduce grain yield by 10 to 40%. Several specialized varieties of the fungus attack many related grasses, including ryegrass (Lolium spp.) and fescue (Festuca spp.) used in lawns.

Photo 2 Clusted cup-like aecia on the underside of a common buckthorn leaf.

In my opinion, the best way to control crown rust of buckthorn is to remove the entire plant. Illinois has designated common buckthorn as an exotic weed. Removing common buckthorn plants will help prevent this invasive species from spreading and will also help to reduce the potential for crown rust on desirable plant species.

Author:
Travis Cleveland

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