Feasibility of using glyphosate to control beach evening primrose Oenothera drummondii in heavily invaded coastal dunes, Odiel Marshes, Spain.
Beach evening primrose Oenothera drummondii is a perennial plant native to the southern USA and adjacent parts of Mexico that invades coastal habitats in several countries. There are currently no accepted control methods. We conducted a seven-month controlled field trial using the glyphosate herbicide Roundup® Ultra Plus in the Odiel Marsh Nature Reserve, Huelva Province, southern Spain. Different herbicide concentrations were tested by knapsack spraying. We estimated the costs of treating an entire invaded nature reserve in southern Spain where O. drummondii has invaded 123 ha of land. A dose of 20 g active ingredient/litre was the minimum effective dose for this species in coastal dunes. As new seedlings appeared after a single herbicide treatment, periodic treatments would be necessary to maintain the population level below an impact threshold. However, the total glyphosate input (710 kg active ingredient/year) to the Reserve for an indefinite period may give rise to social rejection, and demands for the assessment of ecotoxicological impact on native fauna, adjacent habitats and site uses before initiating control actions at full scale. The control costs of the entire 123 ha invaded area for two herbicide applications/year were estimated at Euro 162,000/year (Euro 1,317/ha/year). This includes materials (30% of total costs) and workers (70% of total costs). The study highlights the difficulties and constraints of controlling advanced stages of invasions.