Red Clover Seed Production: V. Root Health and Crop Productivity

Abstract

Red clover (Trifolium pratense L.) is an important forage legume that is primarily grown for seed in western Oregon, but the effects of root health on red clover seed production systems are not well defined. This study was conducted to determine the effects of root health on red clover seed production. Thirty‐one seed fields were selected in spring 1992 and their cultivar identity, age of stand, and seed certification status (seed source groupings) determined by grower interviews and DNA analyses. Two herbage removal time treatments (early May and late June) were applied and the number of flowers and soil water content measured during the period of flowering and seed production. Root rot [Fusarium solani (Kuhn)] and root borer [Hylastinus obscurus (Marsham)] infestation were measured at early herbage removal time and seed harvest. The percentage of plants infested with root borers was the greatest root health determinate of seed yield, regardless of early or late herbage removal time. Seed yield was also correlated with the regrowth and flower production capacity of plants following herbage removal. For both herbage removal times, regrowth after removal was affected by the plant capacity to deplete soil water. Season‐end root borer infestation and soil water depletion amount were inversely related, indicating root integrity affected water utilization. Second‐year seed crops had greater disease and root borer damage than first‐year crops. Late herbage removal time treatments reduced flower density, seed yield, and season‐end phytomass compared with early removal. Genetic selection for improved root borer resistance may be a useful alternative selection strategy to root rot resistance for increasing red clover seed yields.