Agronomic practices for growing houndstongue (Cynoglossum officinale) as a crop for mass-producing a weed biocontrol agent

Houndstongue is a troublesome weed of pasture, rangeland, and open forest in British Columbia, Canada. Recently, a root-feeding weevil was released in Canada that successfully controls houndstongue patches, but it has been difficult to propagate this weevil in sufficient numbers for widespread release. The goal of the current study was to develop methods for growing houndstongue as a crop in a farm-field setting for weevil propagation. Field experiments were conducted to determine optimum seeding dates, depths, and rates for houndstongue. The effects of straw-residue cover and nitrogen-application rates were also examined. More than 90% of the seed used was viable, and about 50% of the planted seed emerged. The most consistent plant densities occurred when houndstongue was seeded in October and had a winter and early spring moist chilling period to break seed dormancy. For fall seeded houndstongue, plants emerged equally well from 2- and 5-cm depths. Houndstongue is moderately responsive to nitrogen fertilizer but usually did not benefit from additional straw cover on the soil before emergence. Houndstongue plants also survived in drought conditions. In conclusion, this weed can be consistently grown as a crop for the propagation of a root-feeding weevil for houndstongue control.