Root Rot Affects Red Clover More Than Other Forage Legumes in Mixed Grass-Legume Leys

Red clover (RC) (Trifolium pratense L.) is the most important forage legume in Swedish mixed grass-legume (MGL) leys. This study evaluated the persistence of two RC cultivars, white clover (WC), birdsfoot trefoil (BT), and lucerne (LU) in mixtures of timothy and meadow fescue associated with root rot (RR). Agronomic performance and nutritive value were measured across 3 years in a field trial conducted across two sites in a 2- or 3-cut regime. Disease progression of RR was assessed each spring and autumn, and symptoms of RR were frequent in the autumn of the seeding year. After two harvest years, all assessed RC roots were severely infected as disease severity index (> 60). The legume proportion (LP) in RC treatments was largest for Years 1 and 2 and significantly decreased by 50% in Year 3. LP in white clover, LU, and BT were lower than in RC, but less affected by RR. LP of WC remained at about 23% for Years 1–3. LP decreased from a low level for BT by 46%, and LP in LU was extremely low. Total annual dry matter (DM) yield was larger for Years 2 and 3 than Year 1 for all treatments and increased in Year 3 for mixtures with WC, BT, and LU. Economically, WC and RC with three cuts were the best options, evaluated as DM yield, digestibility, and protein content. Application of lime, 6 and 9 t ha⁻¹, evaluated in MGL swards in two separate field trials did not affect RC proportion, disease progress, or yield compared to untreated control.