Preventive and Post-Symptom Fungicide Programs Suppress Cumulative Foliar Disease in Rubber Tree Nursery Plants in Côte d’Ivoire

Abstract

Foliar diseases constrain the production of healthy rubber tree planting material in humid tropical nurseries. We tested whether preventive and post-symptom fungicide programmes reduced cumulative foliar disease on Hevea brasiliensis clone IRCA 331 during one nursery season at Bongo, Côte d’Ivoire. The present study analysed two fungicide trials conducted in a rubber nursery at Bongo, southeastern Côte d’Ivoire.  Every active programme reduced cumulative incidence relative to the untreated control (all Holm-adjusted P < 0.001): suppression was 75.3–94.1% in the preventive trial and 88.2–93.6% in the post-symptom trial. Severity on the older first leaf tier did not differ among treatments, whereas severity on newly emerged foliage declined by 60.2–88.9% and 86.4–91.9%, respectively (all Holm-adjusted P < 0.001). Treatment effects on cumulative incidence and new-foliage severity were large (partial eta-squared ≥ 0.864). Tukey-adjusted comparisons identified overlapping efficacy groups among many active programmes; therefore, the smallest numerical estimate did not establish a uniquely superior programme. Adding a spray adjuvant produced no consistent detectable improvement in cumulative disease control. These findings demonstrate strong disease suppression under the tested site, season, and clone, but do not establish broad recommendations or non-inferiority of lower-input programmes. Multi-season, multi-location trials with molecular pathogen confirmation, complete weather and application records, and prespecified agronomic margins are required before operational recommendations are generalised.