Influence of late season harvesting, fall grazing, and fungicide treatment on Verticillium wilt incidence, plant density, and forage yield of alfalfa

Studies were conducted in the presence of Verticillium wilt (Verticillium albo-atrum) to determine the effect of fall harvesting and grazing over time on plant stand and forage yield of alfalfa (Medicago sativa). Resistant and susceptible cultivars were tested on established and newly seeded fields. In the fall (experiments 1 and 2), cultivars were either: (i) cut (third time); (ii) grazed; (iii) cut and grazed; or (iv) left uncut and ungrazed. Although Verticillium was present, test sites for experiments 2 and 3 were sprayed with a spore suspension of V albo-atrum immediately following the first cutting of each experiment to standardize disease pressure. In experiment 1, the moderately resistant cultivar Apollo II, harvested twice without a late third cutting or fall grazing, produced the highest forage yield the following year. Fall grazing reduced subsequent yields in both the 2- and 3-cut treatments. In experiment 2, a third cutting decreased plant density and forage yield in both resistant and susceptible cultivars, while grazing had no effect. Neither fall treatment affected incidence of Verticillium wilt. In experiment 3, application of the fungicide benomyl to plant stubble following each harvest decreased Verticillium wilt in Apollo but not in Arrow. Overall, with the resistant cultivar Arrow, harvesting twice annually and grazing after a killing frost in lieu of late fall cutting slowed disease development, prolonged stand life, and maximized forage yield and quality.