It’s been said that a weed is a plant we haven’t yet found a use for. If that’s the case, western juniper – often viewed as undesirable because of its invasion onto Western rangelands – could be earning a new reputation as a bioherbicide used to kill other weeds.

The observation that juniper trees inhibit the growth of other vegetation around them led to research at Oregon State University by Drs. Pat Dysart and Carol Mallory-Smith, weed scientists in the Department of Crop and Soil Science.

The duo wondered if something in juniper tree chemistry might be killing or retarding the growth of neighboring plants. If so, they hypothesized that it may be possible to use its toxic power as a weed killer.

With initial funding from the Agricultural Research Foundation at Oregon State, the two researchers tested their idea in greenhouse experiments. They found that aqueous extracts made from juniper leaves do inhibit germination of rangeland weeds, such as medusahead and cheatgrass.

The researchers are now taking their experiments to the field to test various ways to apply the juniper – as dried leaves, juniper tea or leaf and stem mulch – and evaluate how well each works to keep weeds from germinating. Their field plots are located in central Oregon on grazing land belonging to the Confederated Tribes of Warm Springs, where they are working with range specialist Jason Smith.

Whether juniper will be developed into a commercial herbicide remains to be seen. But with a $70,000 grant from USDA’s Natural Resources Conservation Service, the research on juniper as a bioherbicide will continue. The researchers plan to develop appropriate application methods and concentrations specific to each growing situation and weeds to be controlled.

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