A pilot study to determine the extent of possible biocontrol resistance in St. John's wort, the effect of St.John's wort on forage availability and alternative tools for control.

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St. John's wort (Hypericum perforatum) is a perennial plant native to Europe that can reproduce and spread**aggressively, particularly in disturbed sites and rangelands. St. John's wort was first document in British**Columbia in 1947 and is an excellent competitor; it diminishes native plant species and can harm livestock in**the process. St. John's wort contains the chemicals hypericin and hyperforin in its leaves. Ingestion of hypericin**results in blisters, reduced reproductive performance, and in rare cases, death in livestock. Hyperforin has been**reported to serve as a defensive compound in response to herbivory.**The biocontrol beetle, Chrysolina hyperici, has historically been an effective biocontrol of St. John's wort. In**southern BC treatment by the beetle as reduced St. John's wort populations to less than 2% of pretreatment**levels. Unfortunately, observations indicate that St. John's wort is resurging on the landscape and the biocontrol**beetles are not performing as well as they have historically. Stressors, such as herbivory, are known to trigger**morphological and chemical predator defense mechanisms in plants, such as the production of toxins. St.**John's wort may have the ability to overproduce toxins hypericin and hyperforin as a predatory defense**mechanism in response to beetle herbivory.**To tackle the issue of resurging St. John's wort in BC, new methods are needed to control St. John's wort. Dow**has herbicides that have historically been effective at controlling St. John's wort. The use of this herbicide may**be needed if the population of St. John's wort has developed resistance to the biocontrol beetle. We will**determine if biocontrol resistance exists and the extent of resistance at 3 sites in BC. We will collaborate with**Corteva Agriscience to: 1) determine if biocontrol resistance is present within St. John's wort populations 2)**test the efficacy of different Corteva Agriscience herbicides on St John's wort populations; and 3) we will**present simple field based techniques for identifying potentially resistant plants and alternative weed control**options for St.John's wort control.