Rumex lunaria is a translocated native species in Lanzarote, Canary Islands, behaving as an invasive plant that threatens conservation efforts in Timanfaya National Park and Los Volcanes Natural Park. This study explores new biocontrol techniques using two fungal strains, Alternaria alternata (strain 739) and Fusarium sp. strain 960, a member of the Fusarium incarnatum-equiseti species complex. The fungi were isolated from wild R. lunaria plants from Lanzarote and inoculated under controlled and natural conditions, in greenhouse and in two field zones of Lanzarote. In the greenhouse assays, plants inoculated via foliar spray with the Alternaria strain 739 showed specific symptoms with both a higher number of necrotic lesions and a higher percentage of affected leaves compared to control up to two weeks of trial. The application of Fusarium strain 960 to the roots led to a significant increase in abscised leaves up to 18 weeks of assessments. In the field assays, Alternaria strain 739 was applied in the summer by spraying on the R. lunaria leaves, gradually affecting the plants although no significant differences were observed in any zone. Fusarium strain 960 was applied in the autumn to the roots hindering leaves production. The patterns in both zones were similar, but faster effects were observed in Tremesana than in Mazo zone. In both field trials, pelargonic acid at 2.5% (w/w) was applied to weaken the plants and assess the duration of its effect on them. Additionally, a combined treatment with Fusarium strain 960 and pelargonic acid was tested to determine whether it enhanced efficacy compared to single applications. Although preliminary, observations under controlled conditions suggest potential for strain application following optimization of formulation and eco-physiological parameters.